@ifinfo
@format
START-INFO-DIR-ENTRY
-* Stabs:: The "stabs" debugging information format.
+* Stabs: (stabs). The "stabs" debugging information format.
END-INFO-DIR-ENTRY
@end format
@end ifinfo
@ifinfo
This document describes the stabs debugging symbol tables.
-Copyright 1992, 1993 Free Software Foundation, Inc.
-Contributed by Cygnus Support. Written by Julia Menapace.
+Copyright 1992,1993,1994,1995,1997,1998,2000,2001
+ Free Software Foundation, Inc.
+Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
+and David MacKenzie.
-Permission is granted to make and distribute verbatim copies of
-this manual provided the copyright notice and this permission notice
-are preserved on all copies.
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.1 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
+and with the Back-Cover Texts as in (a) below.
-@ignore
-Permission is granted to process this file through Tex and print the
-results, provided the printed document carries copying permission
-notice identical to this one except for the removal of this paragraph
-(this paragraph not being relevant to the printed manual).
-
-@end ignore
-Permission is granted to copy or distribute modified versions of this
-manual under the terms of the GPL (for which purpose this text may be
-regarded as a program in the language TeX).
+(a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
+this GNU Manual, like GNU software. Copies published by the Free
+Software Foundation raise funds for GNU development.''
@end ifinfo
@setchapternewpage odd
@settitle STABS
@titlepage
@title The ``stabs'' debug format
-@author Julia Menapace
+@author Julia Menapace, Jim Kingdon, David MacKenzie
@author Cygnus Support
@page
@tex
@end tex
@vskip 0pt plus 1filll
-Copyright @copyright{} 1992, 1993 Free Software Foundation, Inc.
+Copyright @copyright{} 1992,1993,1994,1995,1997,1998,2000,2001 Free Software Foundation, Inc.
Contributed by Cygnus Support.
-Permission is granted to make and distribute verbatim copies of
-this manual provided the copyright notice and this permission notice
-are preserved on all copies.
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.1 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
+and with the Back-Cover Texts as in (a) below.
+
+(a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
+this GNU Manual, like GNU software. Copies published by the Free
+Software Foundation raise funds for GNU development.''
@end titlepage
@menu
* Overview:: Overview of stabs
-* Program structure:: Encoding of the structure of the program
+* Program Structure:: Encoding of the structure of the program
* Constants:: Constants
-* Example:: A comprehensive example in C
* Variables::
* Types:: Type definitions
* Symbol Tables:: Symbol information in symbol tables
-* Cplusplus:: Appendixes:
-* Example2.c:: Source code for extended example
-* Example2.s:: Assembly code for extended example
+* Cplusplus:: Stabs specific to C++
* Stab Types:: Symbol types in a.out files
-* Symbol Descriptors:: Table of Symbol Descriptors
-* Type Descriptors:: Table of Symbol Descriptors
-* Expanded reference:: Reference information by stab type
-* Questions:: Questions and anomolies
-* xcoff-differences:: Differences between GNU stabs in a.out
- and GNU stabs in xcoff
-* Sun-differences:: Differences between GNU stabs and Sun
- native stabs
-* Stabs-in-ELF:: Stabs in an ELF file.
+* Symbol Descriptors:: Table of symbol descriptors
+* Type Descriptors:: Table of type descriptors
+* Expanded Reference:: Reference information by stab type
+* Questions:: Questions and anomalies
+* Stab Sections:: In some object file formats, stabs are
+ in sections.
+* Symbol Types Index:: Index of symbolic stab symbol type names.
@end menu
@end ifinfo
+@c TeX can handle the contents at the start but makeinfo 3.12 can not
+@iftex
+@contents
+@end iftex
@node Overview
-@chapter Overview of stabs
+@chapter Overview of Stabs
@dfn{Stabs} refers to a format for information that describes a program
to a debugger. This format was apparently invented by
-@c FIXME! <<name of inventor>> at
+Peter Kessler at
the University of California at Berkeley, for the @code{pdx} Pascal
debugger; the format has spread widely since then.
This document is one of the few published sources of documentation on
-stabs. It is believed to be completely comprehensive for stabs used by
-C. The lists of symbol descriptors (@pxref{Symbol Descriptors}) and
-type descriptors (@pxref{Type Descriptors}) are believed to be completely
-comprehensive. There are known to be stabs for C++ and COBOL which are
-poorly documented here. Stabs specific to other languages (e.g., Pascal,
-Modula-2) are probably not as well documented as they should be.
-
-Other sources of information on stabs are @cite{dbx and dbxtool
-interfaces}, 2nd edition, by Sun, circa 1988, and @cite{AIX Version 3.2
-Files Reference}, Fourth Edition, September 1992, "dbx Stabstring
-Grammar" in the a.out section, page 2-31. This document is believed to
-incorporate the information from those two sources except where it
-explictly directs you to them for more information.
+stabs. It is believed to be comprehensive for stabs used by C. The
+lists of symbol descriptors (@pxref{Symbol Descriptors}) and type
+descriptors (@pxref{Type Descriptors}) are believed to be completely
+comprehensive. Stabs for COBOL-specific features and for variant
+records (used by Pascal and Modula-2) are poorly documented here.
+
+@c FIXME: Need to document all OS9000 stuff in GDB; see all references
+@c to os9k_stabs in stabsread.c.
+
+Other sources of information on stabs are @cite{Dbx and Dbxtool
+Interfaces}, 2nd edition, by Sun, 1988, and @cite{AIX Version 3.2 Files
+Reference}, Fourth Edition, September 1992, "dbx Stabstring Grammar" in
+the a.out section, page 2-31. This document is believed to incorporate
+the information from those two sources except where it explicitly directs
+you to them for more information.
@menu
* Flow:: Overview of debugging information flow
* Stabs Format:: Overview of stab format
-* String Field:: The @code{.stabs} @var{string} field
-* C example:: A simple example in C source
-* Assembly code:: The simple example at the assembly level
+* String Field:: The string field
+* C Example:: A simple example in C source
+* Assembly Code:: The simple example at the assembly level
@end menu
@node Flow
-@section Overview of debugging information flow
+@section Overview of Debugging Information Flow
The GNU C compiler compiles C source in a @file{.c} file into assembly
language in a @file{.s} file, which the assembler translates into
For some object file formats, the debugging information is encapsulated
in assembler directives known collectively as @dfn{stab} (symbol table)
directives, which are interspersed with the generated code. Stabs are
-the native format for debugging information in the a.out and xcoff
-object file formats. The GNU tools can also emit stabs in the coff and
-ecoff object file formats.
+the native format for debugging information in the a.out and XCOFF
+object file formats. The GNU tools can also emit stabs in the COFF and
+ECOFF object file formats.
The assembler adds the information from stabs to the symbol information
it places by default in the symbol table and the string table of the
a source of debugging information about the program.
@node Stabs Format
-@section Overview of stab format
+@section Overview of Stab Format
There are three overall formats for stab assembler directives,
differentiated by the first word of the stab. The name of the directive
describes which combination of four possible data fields follows. It is
either @code{.stabs} (string), @code{.stabn} (number), or @code{.stabd}
-(dot). IBM's xcoff assembler uses @code{.stabx} (and some other
+(dot). IBM's XCOFF assembler uses @code{.stabx} (and some other
directives such as @code{.file} and @code{.bi}) instead of
@code{.stabs}, @code{.stabn} or @code{.stabd}.
The overall format of each class of stab is:
@example
-.stabs "@var{string}",@var{type},0,@var{desc},@var{value}
-.stabn @var{type},0,@var{desc},@var{value}
-.stabd @var{type},0,@var{desc}
+.stabs "@var{string}",@var{type},@var{other},@var{desc},@var{value}
+.stabn @var{type},@var{other},@var{desc},@var{value}
+.stabd @var{type},@var{other},@var{desc}
.stabx "@var{string}",@var{value},@var{type},@var{sdb-type}
@end example
@c what is the correct term for "current file location"? My AIX
@c assembler manual calls it "the value of the current location counter".
For @code{.stabn} and @code{.stabd}, there is no @var{string} (the
-@code{n_strx} field is zero; see @xref{Symbol Tables}). For
+@code{n_strx} field is zero; see @ref{Symbol Tables}). For
@code{.stabd}, the @var{value} field is implicit and has the value of
the current file location. For @code{.stabx}, the @var{sdb-type} field
-is unused for stabs and can always be set to 0.
+is unused for stabs and can always be set to zero. The @var{other}
+field is almost always unused and can be set to zero.
The number in the @var{type} field gives some basic information about
which type of stab this is (or whether it @emph{is} a stab, as opposed
to an ordinary symbol). Each valid type number defines a different stab
-type. Further, the stab type defines the exact interpretation of, and
+type; further, the stab type defines the exact interpretation of, and
possible values for, any remaining @var{string}, @var{desc}, or
@var{value} fields present in the stab. @xref{Stab Types}, for a list
-in numeric order of the valid type field values for stab directives.
+in numeric order of the valid @var{type} field values for stab directives.
@node String Field
-@section The @code{.stabs} @var{string} field
+@section The String Field
-For @code{.stabs} the @var{string} field holds the meat of the
-debugging information. The generally unstructured nature of this field
+For most stabs the string field holds the meat of the
+debugging information. The flexible nature of this field
is what makes stabs extensible. For some stab types the string field
contains only a name. For other stab types the contents can be a great
deal more complex.
-The overall format is of the @var{string} field is:
+The overall format of the string field for most stab types is:
@example
"@var{name}:@var{symbol-descriptor} @var{type-information}"
@end example
-@var{name} is the name of the symbol represented by the stab.
-@var{name} can be omitted, which means the stab represents an unnamed
-object. For example, @samp{:t10=*2} defines type 10 as a pointer to
-type 2, but does not give the type a name. Omitting the @var{name}
-field is supported by AIX DBX and GDB after about version 4.8, but not
-other debuggers. GCC sometimes uses a single space as the name instead
-of omitting the name altogether; apparently that is supported by most
-debuggers.
+@var{name} is the name of the symbol represented by the stab; it can
+contain a pair of colons (@pxref{Nested Symbols}). @var{name} can be
+omitted, which means the stab represents an unnamed object. For
+example, @samp{:t10=*2} defines type 10 as a pointer to type 2, but does
+not give the type a name. Omitting the @var{name} field is supported by
+AIX dbx and GDB after about version 4.8, but not other debuggers. GCC
+sometimes uses a single space as the name instead of omitting the name
+altogether; apparently that is supported by most debuggers.
-The @var{symbol_descriptor} following the @samp{:} is an alphabetic
+The @var{symbol-descriptor} following the @samp{:} is an alphabetic
character that tells more specifically what kind of symbol the stab
-represents. If the @var{symbol_descriptor} is omitted, but type
+represents. If the @var{symbol-descriptor} is omitted, but type
information follows, then the stab represents a local variable. For a
list of symbol descriptors, see @ref{Symbol Descriptors}. The @samp{c}
symbol descriptor is an exception in that it is not followed by type
information. @xref{Constants}.
-@var{type-information} is either a @var{type_number}, or
-@samp{@var{type_number}=}. The @var{type_number} alone is a type
+@var{type-information} is either a @var{type-number}, or
+@samp{@var{type-number}=}. A @var{type-number} alone is a type
reference, referring directly to a type that has already been defined.
-The @samp{@var{type_number}=} form is a type definition, where the
+The @samp{@var{type-number}=} form is a type definition, where the
number represents a new type which is about to be defined. The type
definition may refer to other types by number, and those type numbers
-may be followed by @samp{=} and nested definitions.
+may be followed by @samp{=} and nested definitions. Also, the Lucid
+compiler will repeat @samp{@var{type-number}=} more than once if it
+wants to define several type numbers at once.
In a type definition, if the character that follows the equals sign is
-non-numeric then it is a @var{type_descriptor}, and tells what kind of
+non-numeric then it is a @var{type-descriptor}, and tells what kind of
type is about to be defined. Any other values following the
-@var{type_descriptor} vary, depending on the @var{type_descriptor}. If
-a number follows the @samp{=} then the number is a @var{type_reference}.
-For a full description of types, @ref{Types}. @xref{Type
-Descriptors}, for a list of
-@var{type_descriptor} values.
+@var{type-descriptor} vary, depending on the @var{type-descriptor}.
+@xref{Type Descriptors}, for a list of @var{type-descriptor} values. If
+a number follows the @samp{=} then the number is a @var{type-reference}.
+For a full description of types, @ref{Types}.
+
+A @var{type-number} is often a single number. The GNU and Sun tools
+additionally permit a @var{type-number} to be a pair
+(@var{file-number},@var{filetype-number}) (the parentheses appear in the
+string, and serve to distinguish the two cases). The @var{file-number}
+is 0 for the base source file, 1 for the first included file, 2 for the
+next, and so on. The @var{filetype-number} is a number starting with
+1 which is incremented for each new type defined in the file.
+(Separating the file number and the type number permits the
+@code{N_BINCL} optimization to succeed more often; see @ref{Include
+Files}).
There is an AIX extension for type attributes. Following the @samp{=}
-is any number of type attributes. Each one starts with @samp{@@} and
-ends with @samp{;}. Debuggers, including AIX's DBX, skip any type
-attributes they do not recognize. GDB 4.9 does not do this---it will
-ignore the entire symbol containing a type attribute. Hopefully this
-will be fixed in the next GDB release. Because of a conflict with C++
+are any number of type attributes. Each one starts with @samp{@@} and
+ends with @samp{;}. Debuggers, including AIX's dbx and GDB 4.10, skip
+any type attributes they do not recognize. GDB 4.9 and other versions
+of dbx may not do this. Because of a conflict with C++
(@pxref{Cplusplus}), new attributes should not be defined which begin
with a digit, @samp{(}, or @samp{-}; GDB may be unable to distinguish
those from the C++ type descriptor @samp{@@}. The attributes are:
@var{boundary} is an integer specifying the alignment. I assume it
applies to all variables of this type.
-@item s@var{size}
-Size in bits of a variable of this type.
-
@item p@var{integer}
Pointer class (for checking). Not sure what this means, or how
@var{integer} is interpreted.
Indicate this is a packed type, meaning that structure fields or array
elements are placed more closely in memory, to save memory at the
expense of speed.
+
+@item s@var{size}
+Size in bits of a variable of this type. This is fully supported by GDB
+4.11 and later.
+
+@item S
+Indicate that this type is a string instead of an array of characters,
+or a bitstring instead of a set. It doesn't change the layout of the
+data being represented, but does enable the debugger to know which type
+it is.
+
+@item V
+Indicate that this type is a vector instead of an array. The only
+major difference between vectors and arrays is that vectors are
+passed by value instead of by reference (vector coprocessor extension).
+
@end table
-All this can make the @var{string} field quite long. All
-versions of GDB, and some versions of DBX, can handle arbitrarily long
-strings. But many versions of DBX cretinously limit the strings to
-about 80 characters, so compilers which must work with such DBX's need
-to split the @code{.stabs} directive into several @code{.stabs}
-directives. Each stab duplicates exactly all but the
-@var{string} field. The @var{string} field of
-every stab except the last is marked as continued with a
-double-backslash at the end. Removing the backslashes and concatenating
-the @var{string} fields of each stab produces the original,
-long string.
-
-@node C example
-@section A simple example in C source
+All of this can make the string field quite long. All versions of GDB,
+and some versions of dbx, can handle arbitrarily long strings. But many
+versions of dbx (or assemblers or linkers, I'm not sure which)
+cretinously limit the strings to about 80 characters, so compilers which
+must work with such systems need to split the @code{.stabs} directive
+into several @code{.stabs} directives. Each stab duplicates every field
+except the string field. The string field of every stab except the last
+is marked as continued with a backslash at the end (in the assembly code
+this may be written as a double backslash, depending on the assembler).
+Removing the backslashes and concatenating the string fields of each
+stab produces the original, long string. Just to be incompatible (or so
+they don't have to worry about what the assembler does with
+backslashes), AIX can use @samp{?} instead of backslash.
+
+@node C Example
+@section A Simple Example in C Source
To get the flavor of how stabs describe source information for a C
program, let's look at the simple program:
to parts of the @file{.s} file in the description of the stabs that
follows.
-@node Assembly code
-@section The simple example at the assembly level
+@node Assembly Code
+@section The Simple Example at the Assembly Level
This simple ``hello world'' example demonstrates several of the stab
types used to describe C language source files.
52 .stabn 224,0,0,LBE2
@end example
-@node Program structure
-@chapter Encoding for the structure of the program
+@node Program Structure
+@chapter Encoding the Structure of the Program
-For the numeric values of the symbolic stab types, see @ref{Stab Types}.
-For a reference to them, see @ref{Expanded reference}.
+The elements of the program structure that stabs encode include the name
+of the main function, the names of the source and include files, the
+line numbers, procedure names and types, and the beginnings and ends of
+blocks of code.
@menu
* Main Program:: Indicate what the main program is
* Include Files:: Names of include files
* Line Numbers::
* Procedures::
+* Nested Procedures::
* Block Structure::
+* Alternate Entry Points:: Entering procedures except at the beginning.
@end menu
@node Main Program
@section Main Program
+@findex N_MAIN
Most languages allow the main program to have any name. The
-@code{N_MAIN} stab type is used for a stab telling the debugger what
-name is used in this program. Only the name is significant; it will be
-the name of a function which is the main program. Most C compilers do
-not use this stab; they expect the debugger to simply assume that the
-name is @samp{main}, but some C compilers emit an @code{N_MAIN} stab for
-the @samp{main} function.
+@code{N_MAIN} stab type tells the debugger the name that is used in this
+program. Only the string field is significant; it is the name of
+a function which is the main program. Most C compilers do not use this
+stab (they expect the debugger to assume that the name is @code{main}),
+but some C compilers emit an @code{N_MAIN} stab for the @code{main}
+function. I'm not sure how XCOFF handles this.
@node Source Files
-@section Paths and names of the source files
+@section Paths and Names of the Source Files
+@findex N_SO
Before any other stabs occur, there must be a stab specifying the source
file. This information is contained in a symbol of stab type
-@code{N_SO}; the string contains the name of the file. The value of the
-symbol is the start address of portion of the text section corresponding
-to that file.
+@code{N_SO}; the string field contains the name of the file. The
+value of the symbol is the start address of the portion of the
+text section corresponding to that file.
-With the Sun Solaris2 compiler, the @code{desc} field contains a
+With the Sun Solaris2 compiler, the desc field contains a
source-language code.
+@c Do the debuggers use it? What are the codes? -djm
Some compilers (for example, GCC2 and SunOS4 @file{/bin/cc}) also
include the directory in which the source was compiled, in a second
@code{N_SO} symbol preceding the one containing the file name. This
symbol can be distinguished by the fact that it ends in a slash. Code
-from the cfront C++ compiler can have additional @code{N_SO} symbols for
+from the @code{cfront} C++ compiler can have additional @code{N_SO} symbols for
nonexistent source files after the @code{N_SO} for the real source file;
these are believed to contain no useful information.
Ltext0:
@end example
+@findex C_FILE
Instead of @code{N_SO} symbols, XCOFF uses a @code{.file} assembler
-directive which assembles to a standard COFF @code{.file} symbol;
-explaining this in detail is outside the scope of this document.
+directive which assembles to a @code{C_FILE} symbol; explaining this in
+detail is outside the scope of this document.
+
+@c FIXME: Exactly when should the empty N_SO be used? Why?
+If it is useful to indicate the end of a source file, this is done with
+an @code{N_SO} symbol with an empty string for the name. The value is
+the address of the end of the text section for the file. For some
+systems, there is no indication of the end of a source file, and you
+just need to figure it ended when you see an @code{N_SO} for a different
+source file, or a symbol ending in @code{.o} (which at least some
+linkers insert to mark the start of a new @code{.o} file).
@node Include Files
-@section Names of include files
+@section Names of Include Files
-There are several different schemes for dealing with include files: the
+There are several schemes for dealing with include files: the
traditional @code{N_SOL} approach, Sun's @code{N_BINCL} approach, and the
XCOFF @code{C_BINCL} approach (which despite the similar name has little in
common with @code{N_BINCL}).
+@findex N_SOL
An @code{N_SOL} symbol specifies which include file subsequent symbols
refer to. The string field is the name of the file and the value is the
-text address corresponding to the start of the previous include file and
+text address corresponding to the end of the previous include file and
the start of this one. To specify the main source file again, use an
@code{N_SOL} symbol with the name of the main source file.
-A @code{N_BINCL} symbol specifies the start of an include file. In an
-object file, only the name is significant. The Sun linker puts data
-into some of the other fields. The end of the include file is marked by
-a @code{N_EINCL} symbol (which has no name field). In an ojbect file,
-there is no significant data in the @code{N_EINCL} symbol; the Sun
-linker puts data into some of the fields. @code{N_BINCL} and
-@code{N_EINCL} can be nested. If the linker detects that two source
-files have identical stabs with a @code{N_BINCL} and @code{N_EINCL} pair
-(as will generally be the case for a header file), then it only puts out
-the stabs once. Each additional occurance is replaced by an
-@code{N_EXCL} symbol. I believe the Sun (SunOS4, not sure about
-Solaris) linker is the only one which supports this feature.
-
+@findex N_BINCL
+@findex N_EINCL
+@findex N_EXCL
+The @code{N_BINCL} approach works as follows. An @code{N_BINCL} symbol
+specifies the start of an include file. In an object file, only the
+string is significant; the linker puts data into some of the other
+fields. The end of the include file is marked by an @code{N_EINCL}
+symbol (which has no string field). In an object file, there is no
+significant data in the @code{N_EINCL} symbol. @code{N_BINCL} and
+@code{N_EINCL} can be nested.
+
+If the linker detects that two source files have identical stabs between
+an @code{N_BINCL} and @code{N_EINCL} pair (as will generally be the case
+for a header file), then it only puts out the stabs once. Each
+additional occurrence is replaced by an @code{N_EXCL} symbol. I believe
+the GNU linker and the Sun (both SunOS4 and Solaris) linker are the only
+ones which supports this feature.
+
+A linker which supports this feature will set the value of a
+@code{N_BINCL} symbol to the total of all the characters in the stabs
+strings included in the header file, omitting any file numbers. The
+value of an @code{N_EXCL} symbol is the same as the value of the
+@code{N_BINCL} symbol it replaces. This information can be used to
+match up @code{N_EXCL} and @code{N_BINCL} symbols which have the same
+filename. The @code{N_EINCL} value, and the values of the other and
+description fields for all three, appear to always be zero.
+
+@findex C_BINCL
+@findex C_EINCL
For the start of an include file in XCOFF, use the @file{.bi} assembler
directive, which generates a @code{C_BINCL} symbol. A @file{.ei}
directive, which generates a @code{C_EINCL} symbol, denotes the end of
the include file. Both directives are followed by the name of the
-source file in quotes, which becomes the string for the symbol. The
-value of each symbol, produced automatically by the assembler and
-linker, is an offset into the executable which points to the beginning
-(inclusive, as you'd expect) and end (inclusive, as you would not
-expect) of the portion of the COFF linetable which corresponds to this
-include file. @code{C_BINCL} and @code{C_EINCL} do not nest.
+source file in quotes, which becomes the string for the symbol.
+The value of each symbol, produced automatically by the assembler
+and linker, is the offset into the executable of the beginning
+(inclusive, as you'd expect) or end (inclusive, as you would not expect)
+of the portion of the COFF line table that corresponds to this include
+file. @code{C_BINCL} and @code{C_EINCL} do not nest.
@node Line Numbers
@section Line Numbers
-A @code{N_SLINE} symbol represents the start of a source line. The
-@var{desc} field contains the line number and the @var{value} field
-contains the code address for the start of that source line. On most
-machines the address is absolute; for Sun's stabs-in-ELF, it is relative
-to the function in which the @code{N_SLINE} symbol occurs.
+@findex N_SLINE
+An @code{N_SLINE} symbol represents the start of a source line. The
+desc field contains the line number and the value contains the code
+address for the start of that source line. On most machines the address
+is absolute; for stabs in sections (@pxref{Stab Sections}), it is
+relative to the function in which the @code{N_SLINE} symbol occurs.
+@findex N_DSLINE
+@findex N_BSLINE
GNU documents @code{N_DSLINE} and @code{N_BSLINE} symbols for line
numbers in the data or bss segments, respectively. They are identical
to @code{N_SLINE} but are relocated differently by the linker. They
were intended to be used to describe the source location of a variable
declaration, but I believe that GCC2 actually puts the line number in
the desc field of the stab for the variable itself. GDB has been
-ignoring these symbols (unless they contain a string field) at least
-since GDB 3.5.
-
-XCOFF uses COFF line numbers instead, which are outside the scope of
-this document, ammeliorated by adequate marking of include files
-(@pxref{Source Files}).
+ignoring these symbols (unless they contain a string field) since
+at least GDB 3.5.
For single source lines that generate discontiguous code, such as flow
of control statements, there may be more than one line number entry for
the same source line. In this case there is a line number entry at the
start of each code range, each with the same line number.
+XCOFF does not use stabs for line numbers. Instead, it uses COFF line
+numbers (which are outside the scope of this document). Standard COFF
+line numbers cannot deal with include files, but in XCOFF this is fixed
+with the @code{C_BINCL} method of marking include files (@pxref{Include
+Files}).
+
@node Procedures
@section Procedures
-All of the following stabs use the @code{N_FUN} symbol type.
-
-A function is represented by an @samp{F} symbol descriptor (@var{desc}
-field) for a global (extern) function, and @samp{f} for a static (local)
-function. The next @code{N_SLINE} symbol can be used to find the line
-number of the start of the function. The value field is the address of
-the start of the function (absolute for @code{a.out}; relative to the
-start of the file for Sun's stabs-in-ELF). The type information of the
-stab represents the return type of the function; thus @samp{foo:f5}
-means that foo is a function returning type 5.
-
-The type information of the stab is optionally followed by type
-information for each argument, with each argument preceded by @samp{;}.
-An argument type of 0 means that additional arguments are being passed,
-whose types and number may vary (@samp{...} in ANSI C). This extension
-is used by Sun's Solaris compiler. GDB has tolerated it (i.e., at least
-parsed the syntax, if not necessarily used the information) at least
-since version 4.8; I don't know whether all versions of DBX will
-tolerate it. The argument types given here are not redundant
-with the symbols for the arguments themselves (@pxref{Parameters}), they
-are the types of the arguments as they are passed, before any
-conversions might take place. For example, if a C function which is
-declared without a prototype takes a @code{float} argument, the value is
-passed as a @code{double} but then converted to a @code{float}.
-Debuggers need to use the types given in the arguments when printing
-values, but if calling the function they need to use the types given in
-the symbol defining the function.
+@findex N_FUN, for functions
+@findex N_FNAME
+@findex N_STSYM, for functions (Sun acc)
+@findex N_GSYM, for functions (Sun acc)
+All of the following stabs normally use the @code{N_FUN} symbol type.
+However, Sun's @code{acc} compiler on SunOS4 uses @code{N_GSYM} and
+@code{N_STSYM}, which means that the value of the stab for the function
+is useless and the debugger must get the address of the function from
+the non-stab symbols instead. On systems where non-stab symbols have
+leading underscores, the stabs will lack underscores and the debugger
+needs to know about the leading underscore to match up the stab and the
+non-stab symbol. BSD Fortran is said to use @code{N_FNAME} with the
+same restriction; the value of the symbol is not useful (I'm not sure it
+really does use this, because GDB doesn't handle this and no one has
+complained).
+
+@findex C_FUN
+A function is represented by an @samp{F} symbol descriptor for a global
+(extern) function, and @samp{f} for a static (local) function. For
+a.out, the value of the symbol is the address of the start of the
+function; it is already relocated. For stabs in ELF, the SunPRO
+compiler version 2.0.1 and GCC put out an address which gets relocated
+by the linker. In a future release SunPRO is planning to put out zero,
+in which case the address can be found from the ELF (non-stab) symbol.
+Because looking things up in the ELF symbols would probably be slow, I'm
+not sure how to find which symbol of that name is the right one, and
+this doesn't provide any way to deal with nested functions, it would
+probably be better to make the value of the stab an address relative to
+the start of the file, or just absolute. See @ref{ELF Linker
+Relocation} for more information on linker relocation of stabs in ELF
+files. For XCOFF, the stab uses the @code{C_FUN} storage class and the
+value of the stab is meaningless; the address of the function can be
+found from the csect symbol (XTY_LD/XMC_PR).
+
+The type information of the stab represents the return type of the
+function; thus @samp{foo:f5} means that foo is a function returning type
+5. There is no need to try to get the line number of the start of the
+function from the stab for the function; it is in the next
+@code{N_SLINE} symbol.
+
+@c FIXME: verify whether the "I suspect" below is true or not.
+Some compilers (such as Sun's Solaris compiler) support an extension for
+specifying the types of the arguments. I suspect this extension is not
+used for old (non-prototyped) function definitions in C. If the
+extension is in use, the type information of the stab for the function
+is followed by type information for each argument, with each argument
+preceded by @samp{;}. An argument type of 0 means that additional
+arguments are being passed, whose types and number may vary (@samp{...}
+in ANSI C). GDB has tolerated this extension (parsed the syntax, if not
+necessarily used the information) since at least version 4.8; I don't
+know whether all versions of dbx tolerate it. The argument types given
+here are not redundant with the symbols for the formal parameters
+(@pxref{Parameters}); they are the types of the arguments as they are
+passed, before any conversions might take place. For example, if a C
+function which is declared without a prototype takes a @code{float}
+argument, the value is passed as a @code{double} but then converted to a
+@code{float}. Debuggers need to use the types given in the arguments
+when printing values, but when calling the function they need to use the
+types given in the symbol defining the function.
If the return type and types of arguments of a function which is defined
in another source file are specified (i.e., a function prototype in ANSI
type of the function, followed by the arguments, each preceded by
@samp{;}, as in a stab with symbol descriptor @samp{f} or @samp{F}.
This use of symbol descriptor @samp{P} can be distinguished from its use
-for register parameters (@pxref{Parameters}) by the fact that it has
+for register parameters (@pxref{Register Parameters}) by the fact that it has
symbol type @code{N_FUN}.
The AIX documentation also defines symbol descriptor @samp{J} as an
These symbol descriptors are unusual in that they are not followed by
type information.
-For any of the above symbol descriptors, after the symbol descriptor and
-the type information, there is optionally a comma, followed by the name
-of the procedure, followed by a comma, followed by a name specifying the
-scope. The first name is local to the scope specified, and seems to be
-redundant with the name of the symbol (before the @samp{:}). The name
-specifying the scope is the name of a procedure specifying that scope.
-This feature is used by GCC, and presumably Pascal, Modula-2, etc.,
-compilers, for nested functions.
+The following example shows a stab for a function @code{main} which
+returns type number @code{1}. The @code{_main} specified for the value
+is a reference to an assembler label which is used to fill in the start
+address of the function.
+
+@example
+.stabs "main:F1",36,0,0,_main # @r{36 is N_FUN}
+@end example
+
+The stab representing a procedure is located immediately following the
+code of the procedure. This stab is in turn directly followed by a
+group of other stabs describing elements of the procedure. These other
+stabs describe the procedure's parameters, its block local variables, and
+its block structure.
+
+If functions can appear in different sections, then the debugger may not
+be able to find the end of a function. Recent versions of GCC will mark
+the end of a function with an @code{N_FUN} symbol with an empty string
+for the name. The value is the address of the end of the current
+function. Without such a symbol, there is no indication of the address
+of the end of a function, and you must assume that it ended at the
+starting address of the next function or at the end of the text section
+for the program.
+
+@node Nested Procedures
+@section Nested Procedures
+
+For any of the symbol descriptors representing procedures, after the
+symbol descriptor and the type information is optionally a scope
+specifier. This consists of a comma, the name of the procedure, another
+comma, and the name of the enclosing procedure. The first name is local
+to the scope specified, and seems to be redundant with the name of the
+symbol (before the @samp{:}). This feature is used by GCC, and
+presumably Pascal, Modula-2, etc., compilers, for nested functions.
If procedures are nested more than one level deep, only the immediately
-containing scope is specified, for example:
+containing scope is specified. For example, this code:
@example
int
.stabs "foo:F1",36,0,0,_foo
@end example
-The stab representing a procedure is located immediately following the
-code of the procedure. This stab is in turn directly followed by a
-group of other stabs describing elements of the procedure. These other
-stabs describe the procedure's parameters, its block local variables, and
-its block structure.
-
-Going back to our "hello world" example program,
-
-@example
-48 ret
-49 restore
-@end example
-
-@noindent
-The @code{.stabs} entry after this code fragment shows the @var{name} of
-the procedure (@code{main}); the type descriptor @var{desc} (@code{F},
-for a global procedure); a reference to the predefined type @code{int}
-for the return type; and the starting @var{address} of the procedure.
-
-Here is an exploded summary (with whitespace introduced for clarity),
-followed by line 50 of our sample assembly output, which has this form:
-
-@example
-.stabs "@var{name}:
- @var{desc} @r{(global proc @samp{F})}
- @var{return_type_ref} @r{(int)}
- ",N_FUN, NIL, NIL,
- @var{address}
-@end example
-
-@example
-50 .stabs "main:F1",36,0,0,_main
-@end example
-
@node Block Structure
@section Block Structure
+@findex N_LBRAC
+@findex N_RBRAC
+@c For GCC 2.5.8 or so stabs-in-coff, these are absolute instead of
+@c function relative (as documented below). But GDB has never been able
+@c to deal with that (it had wanted them to be relative to the file, but
+@c I just fixed that (between GDB 4.12 and 4.13)), so it is function
+@c relative just like ELF and SOM and the below documentation.
The program's block structure is represented by the @code{N_LBRAC} (left
brace) and the @code{N_RBRAC} (right brace) stab types. The variables
-defined inside a block preceded the @code{N_LBRAC} symbol for most
+defined inside a block precede the @code{N_LBRAC} symbol for most
compilers, including GCC. Other compilers, such as the Convex, Acorn
-RISC machine, and Sun acc compilers, put the variables after the
+RISC machine, and Sun @code{acc} compilers, put the variables after the
@code{N_LBRAC} symbol. The values of the @code{N_LBRAC} and
@code{N_RBRAC} symbols are the start and end addresses of the code of
the block, respectively. For most machines, they are relative to the
starting address of this source file. For the Gould NP1, they are
-absolute. For Sun's stabs-in-ELF, they are relative to the function in
-which they occur.
+absolute. For stabs in sections (@pxref{Stab Sections}), they are
+relative to the function in which they occur.
The @code{N_LBRAC} and @code{N_RBRAC} stabs that describe the block
scope of a procedure are located after the @code{N_FUN} stab that
represents the procedure itself.
-Sun documents the @code{desc} field of @code{N_LBRAC} and
+Sun documents the desc field of @code{N_LBRAC} and
@code{N_RBRAC} symbols as containing the nesting level of the block.
-However, DBX seems not to care, and GCC always sets @code{desc} to
+However, dbx seems to not care, and GCC always sets desc to
zero.
+@findex .bb
+@findex .be
+@findex C_BLOCK
+For XCOFF, block scope is indicated with @code{C_BLOCK} symbols. If the
+name of the symbol is @samp{.bb}, then it is the beginning of the block;
+if the name of the symbol is @samp{.be}; it is the end of the block.
+
+@node Alternate Entry Points
+@section Alternate Entry Points
+
+@findex N_ENTRY
+@findex C_ENTRY
+Some languages, like Fortran, have the ability to enter procedures at
+some place other than the beginning. One can declare an alternate entry
+point. The @code{N_ENTRY} stab is for this; however, the Sun FORTRAN
+compiler doesn't use it. According to AIX documentation, only the name
+of a @code{C_ENTRY} stab is significant; the address of the alternate
+entry point comes from the corresponding external symbol. A previous
+revision of this document said that the value of an @code{N_ENTRY} stab
+was the address of the alternate entry point, but I don't know the
+source for that information.
+
@node Constants
@chapter Constants
@item e @var{type-information} , @var{value}
Constant whose value can be represented as integral.
@var{type-information} is the type of the constant, as it would appear
-after a symbol descriptor (@pxref{Stabs Format}). @var{value} is the
+after a symbol descriptor (@pxref{String Field}). @var{value} is the
numeric value of the constant. GDB 4.9 does not actually get the right
value if @var{value} does not fit in a host @code{int}, but it does not
do anything violent, and future debuggers could be extended to accept
@item S @var{type-information} , @var{elements} , @var{bits} , @var{pattern}
Set constant. @var{type-information} is the type of the constant, as it
-would appear after a symbol descriptor (@pxref{Stabs Format}).
-@var{elements} is the number of elements in the set (Does this means
+would appear after a symbol descriptor (@pxref{String Field}).
+@var{elements} is the number of elements in the set (does this means
how many bits of @var{pattern} are actually used, which would be
redundant with the type, or perhaps the number of bits set in
@var{pattern}? I don't get it), @var{bits} is the number of bits in the
@end table
The boolean, character, string, and set constants are not supported by
-GDB 4.9, but it will ignore them. GDB 4.8 and earlier gave an error
+GDB 4.9, but it ignores them. GDB 4.8 and earlier gave an error
message and refused to read symbols from the file containing the
constants.
-This information is followed by @samp{;}.
-
-@node Example
-@chapter A Comprehensive Example in C
-
-To describe the other stab types,
-we'll examine a second program, @code{example2}, which builds on the
-first example to introduce the rest of the stab types, symbol
-descriptors, and type descriptors used in C.
-@xref{Example2.c} for the complete @file{.c} source,
-and @pxref{Example2.s} for the @file{.s} assembly code.
-This description includes parts of those files.
-
-@section Flow of control and nested scopes
-
-@table @strong
-@item Directive:
-@code{.stabn}
-@item Types:
-@code{N_SLINE}, @code{N_LBRAC}, @code{N_RBRAC} (cont.)
-@end table
-
-Consider the body of @code{main}, from @file{example2.c}. It shows more
-about how @code{N_SLINE}, @code{N_RBRAC}, and @code{N_LBRAC} stabs are used.
-
-@example
-20 @{
-21 static float s_flap;
-22 int times;
-23 for (times=0; times < s_g_repeat; times++)@{
-24 int inner;
-25 printf ("Hello world\n");
-26 @}
-27 @};
-@end example
-
-Here we have a single source line, the @code{for} line, that generates
-non-linear flow of control, and non-contiguous code. In this case, an
-@code{N_SLINE} stab with the same line number proceeds each block of
-non-contiguous code generated from the same source line.
-
-The example also shows nested scopes. The @code{N_LBRAC} and
-@code{N_LBRAC} stabs that describe block structure are nested in the
-same order as the corresponding code blocks, those of the for loop
-inside those for the body of main.
-
-@noindent
-This is the label for the @code{N_LBRAC} (left brace) stab marking the
-start of @code{main}.
-
-@example
-57 LBB2:
-@end example
-
-@noindent
-In the first code range for C source line 23, the @code{for} loop
-initialize and test, @code{N_SLINE} (68) records the line number:
-
-@example
-.stabn N_SLINE, NIL,
- @var{line},
- @var{address}
-
-58 .stabn 68,0,23,LM2
-59 LM2:
-60 st %g0,[%fp-20]
-61 L2:
-62 sethi %hi(_s_g_repeat),%o0
-63 ld [%fp-20],%o1
-64 ld [%o0+%lo(_s_g_repeat)],%o0
-65 cmp %o1,%o0
-66 bge L3
-67 nop
-
-@exdent label for the @code{N_LBRAC} (start block) marking the start of @code{for} loop
-
-68 LBB3:
-69 .stabn 68,0,25,LM3
-70 LM3:
-71 sethi %hi(LC0),%o1
-72 or %o1,%lo(LC0),%o0
-73 call _printf,0
-74 nop
-75 .stabn 68,0,26,LM4
-76 LM4:
-
-@exdent label for the @code{N_RBRAC} (end block) stab marking the end of the @code{for} loop
-
-77 LBE3:
-@end example
-
-@noindent
-Now we come to the second code range for source line 23, the @code{for}
-loop increment and return. Once again, @code{N_SLINE} (68) records the
-source line number:
-
-@example
-.stabn, N_SLINE, NIL,
- @var{line},
- @var{address}
-
-78 .stabn 68,0,23,LM5
-79 LM5:
-80 L4:
-81 ld [%fp-20],%o0
-82 add %o0,1,%o1
-83 st %o1,[%fp-20]
-84 b,a L2
-85 L3:
-86 .stabn 68,0,27,LM6
-87 LM6:
-
-@exdent label for the @code{N_RBRAC} (end block) stab marking the end of the @code{for} loop
-
-88 LBE2:
-89 .stabn 68,0,27,LM7
-90 LM7:
-91 L1:
-92 ret
-93 restore
-94 .stabs "main:F1",36,0,0,_main
-95 .stabs "argc:p1",160,0,0,68
-96 .stabs "argv:p20=*21=*2",160,0,0,72
-97 .stabs "s_flap:V12",40,0,0,_s_flap.0
-98 .stabs "times:1",128,0,0,-20
-@end example
-
-@noindent
-Here is an illustration of stabs describing nested scopes. The scope
-nesting is reflected in the nested bracketing stabs (@code{N_LBRAC},
-192, appears here).
-
-@example
-.stabn N_LBRAC,NIL,NIL,
- @var{block-start-address}
-
-99 .stabn 192,0,0,LBB2 ## begin proc label
-100 .stabs "inner:1",128,0,0,-24
-101 .stabn 192,0,0,LBB3 ## begin for label
-@end example
-
-@noindent
-@code{N_RBRAC} (224), ``right brace'' ends a lexical block (scope).
-
-@example
-.stabn N_RBRAC,NIL,NIL,
- @var{block-end-address}
-
-102 .stabn 224,0,0,LBE3 ## end for label
-103 .stabn 224,0,0,LBE2 ## end proc label
-@end example
+The above information is followed by @samp{;}.
@node Variables
@chapter Variables
+Different types of stabs describe the various ways that variables can be
+allocated: on the stack, globally, in registers, in common blocks,
+statically, or as arguments to a function.
+
@menu
* Stack Variables:: Variables allocated on the stack.
* Global Variables:: Variables used by more than one source file.
-* Register variables:: Variables in registers.
+* Register Variables:: Variables in registers.
* Common Blocks:: Variables statically allocated together.
* Statics:: Variables local to one source file.
+* Based Variables:: Fortran pointer based variables.
* Parameters:: Variables for arguments to functions.
@end menu
@node Stack Variables
@section Automatic Variables Allocated on the Stack
-If a variable is declared whose scope is local to a function and whose
-lifetime is only as long as that function executes (C calls such
-variables automatic), they can be allocated in a register
-(@pxref{Register variables}) or on the stack.
+If a variable's scope is local to a function and its lifetime is only as
+long as that function executes (C calls such variables
+@dfn{automatic}), it can be allocated in a register (@pxref{Register
+Variables}) or on the stack.
-For variables allocated on the stack, each variable has a stab with the
-symbol descriptor omitted. Since type information should being with a
-digit, @samp{-}, or @samp{(}, only digits, @samp{-}, and @samp{(} are
-precluded from being used for symbol descriptors by this fact. However,
-the Acorn RISC machine (ARM) is said to get this wrong: it puts out a
-mere type definition here, without the preceding
-@code{@var{typenumber}=}. This is a bad idea; there is no guarantee
-that type descriptors are distinct from symbol descriptors.
+@findex N_LSYM, for stack variables
+@findex C_LSYM
+Each variable allocated on the stack has a stab with the symbol
+descriptor omitted. Since type information should begin with a digit,
+@samp{-}, or @samp{(}, only those characters precluded from being used
+for symbol descriptors. However, the Acorn RISC machine (ARM) is said
+to get this wrong: it puts out a mere type definition here, without the
+preceding @samp{@var{type-number}=}. This is a bad idea; there is no
+guarantee that type descriptors are distinct from symbol descriptors.
+Stabs for stack variables use the @code{N_LSYM} stab type, or
+@code{C_LSYM} for XCOFF.
-These stabs have the @code{N_LSYM} stab type. The value of the stab is
-the offset of the variable within the local variables. On most machines
-this is an offset from the frame pointer and is negative.
+The value of the stab is the offset of the variable within the
+local variables. On most machines this is an offset from the frame
+pointer and is negative. The location of the stab specifies which block
+it is defined in; see @ref{Block Structure}.
-The stab for an automatic variable is located just before the
-@code{N_LBRAC} stab describing the open brace of the block to which it
-is scoped, except for some compilers which put the automatic variables
-after the @code{N_LBRAC} (see @code{VARIABLES_INSIDE_BLOCK} in GDB).
-
-For example, the following C code
+For example, the following C code:
@example
int
@}
@end example
-produces the following stabs
+produces the following stabs:
@example
.stabs "main:F1",36,0,0,_main # @r{36 is N_FUN}
.stabn 224,0,0,LBE2 # @r{224 is N_RBRAC}
@end example
-@xref{Procedures} for more information on the first stab, and @ref{Block
-Structure} for more information on the @code{N_LBRAC} and @code{N_RBRAC}
-stabs.
+See @ref{Procedures} for more information on the @code{N_FUN} stab, and
+@ref{Block Structure} for more information on the @code{N_LBRAC} and
+@code{N_RBRAC} stabs.
@node Global Variables
@section Global Variables
-A variable whose scope which is not specific to just one source file is
+@findex N_GSYM
+@findex C_GSYM
+@c FIXME: verify for sure that it really is C_GSYM on XCOFF
+A variable whose scope is not specific to just one source file is
represented by the @samp{G} symbol descriptor. These stabs use the
-@code{N_GSYM} stab type. The type information for the stab
-(@pxref{Stabs Format}) gives the type of the variable.
+@code{N_GSYM} stab type (C_GSYM for XCOFF). The type information for
+the stab (@pxref{String Field}) gives the type of the variable.
For example, the following source code:
the @code{.global _g_foo} and @code{_g_foo:} lines tell the assembler to
produce an external symbol.
-@node Register variables
-@section Register variables
+Some compilers, like GCC, output @code{N_GSYM} stabs only once, where
+the variable is defined. Other compilers, like SunOS4 /bin/cc, output a
+@code{N_GSYM} stab for each compilation unit which references the
+variable.
+
+@node Register Variables
+@section Register Variables
+@findex N_RSYM
+@findex C_RSYM
@c According to an old version of this manual, AIX uses C_RPSYM instead
@c of C_RSYM. I am skeptical; this should be verified.
-Register variables have their own stab type, @code{N_RSYM}, and their
-own symbol descriptor, @code{r}. The stab's value field contains the
-number of the register where the variable data will be stored.
-
-The value is the register number.
+Register variables have their own stab type, @code{N_RSYM}
+(@code{C_RSYM} for XCOFF), and their own symbol descriptor, @samp{r}.
+The stab's value is the number of the register where the variable data
+will be stored.
+@c .stabs "name:type",N_RSYM,0,RegSize,RegNumber (Sun doc)
AIX defines a separate symbol descriptor @samp{d} for floating point
registers. This seems unnecessary; why not just just give floating
the compiler actually uses @samp{d}.
If the register is explicitly allocated to a global variable, but not
-initialized, as in
+initialized, as in:
@example
register int g_bar asm ("%g5");
@end example
-the stab may be emitted at the end of the object file, with
+@noindent
+then the stab may be emitted at the end of the object file, with
the other bss symbols.
@node Common Blocks
A common block is a statically allocated section of memory which can be
referred to by several source files. It may contain several variables.
-I believe Fortran is the only language with this feature. A
-@code{N_BCOMM} stab begins a common block and an @code{N_ECOMM} stab
-ends it. The only thing which is significant about these two stabs is
-their name, which can be used to look up a normal (non-debugging) symbol
-which gives the address of the common block. Then each stab between the
-@code{N_BCOMM} and the @code{N_ECOMM} specifies a member of that common
-block; its value is the offset within the common block of that variable.
-The @code{N_ECOML} stab type is documented for this purpose, but Sun's
-Fortran compiler uses @code{N_GSYM} instead. The test case I
-looked at had a common block local to a function and it used the
-@samp{V} symbol descriptor; I assume one would use @samp{S} if not local
-to a function (that is, if a common block @emph{can} be anything other
-than local to a function).
+I believe Fortran is the only language with this feature.
+
+@findex N_BCOMM
+@findex N_ECOMM
+@findex C_BCOMM
+@findex C_ECOMM
+A @code{N_BCOMM} stab begins a common block and an @code{N_ECOMM} stab
+ends it. The only field that is significant in these two stabs is the
+string, which names a normal (non-debugging) symbol that gives the
+address of the common block. According to IBM documentation, only the
+@code{N_BCOMM} has the name of the common block (even though their
+compiler actually puts it both places).
+
+@findex N_ECOML
+@findex C_ECOML
+The stabs for the members of the common block are between the
+@code{N_BCOMM} and the @code{N_ECOMM}; the value of each stab is the
+offset within the common block of that variable. IBM uses the
+@code{C_ECOML} stab type, and there is a corresponding @code{N_ECOML}
+stab type, but Sun's Fortran compiler uses @code{N_GSYM} instead. The
+variables within a common block use the @samp{V} symbol descriptor (I
+believe this is true of all Fortran variables). Other stabs (at least
+type declarations using @code{C_DECL}) can also be between the
+@code{N_BCOMM} and the @code{N_ECOMM}.
@node Statics
@section Static Variables
Initialized static variables are represented by the @samp{S} and
@samp{V} symbol descriptors. @samp{S} means file scope static, and
-@samp{V} means procedure scope static.
+@samp{V} means procedure scope static. One exception: in XCOFF, IBM's
+xlc compiler always uses @samp{V}, and whether it is file scope or not
+is distinguished by whether the stab is located within a function.
@c This is probably not worth mentioning; it is only true on the sparc
@c for `double' variables which although declared const are actually in
@c the data segment (the text segment can't guarantee 8 byte alignment).
@c (although GCC
-@c 2.4.5 has a bug in that it uses @code{N_FUN}, so neither DBX nor GDB can
+@c 2.4.5 has a bug in that it uses @code{N_FUN}, so neither dbx nor GDB can
@c find the variables)
-In a.out files, @code{N_STSYM} means the data segment, @code{N_FUN}
-means the text segment, and @code{N_LCSYM} means the bss segment.
-
-In xcoff files, each symbol has a section number, so the stab type
-need not indicate the segment.
-
-In ecoff files, the storage class is used to specify the section, so the
-stab type need not indicate the segment.
+@findex N_STSYM
+@findex N_LCSYM
+@findex N_FUN, for variables
+@findex N_ROSYM
+In a.out files, @code{N_STSYM} means the data section, @code{N_FUN}
+means the text section, and @code{N_LCSYM} means the bss section. For
+those systems with a read-only data section separate from the text
+section (Solaris), @code{N_ROSYM} means the read-only data section.
-@c In ELF files, it apparently is a big mess. See kludge in dbxread.c
-@c in GDB. FIXME: Investigate where this kludge comes from.
-@c
-@c This is the place to mention N_ROSYM; I'd rather do so once I can
-@c coherently explain how this stuff works for stabs-in-ELF.
-@c
-For example, the source lines
+For example, the source lines:
@example
static const int var_const = 5;
@example
.stabs "var_const:S1",36,0,0,_var_const # @r{36 is N_FUN}
-. . .
+@dots{}
.stabs "var_init:S1",38,0,0,_var_init # @r{38 is N_STSYM}
-. . .
+@dots{}
.stabs "var_noinit:S1",40,0,0,_var_noinit # @r{40 is N_LCSYM}
@end example
+@findex C_STSYM
+@findex C_BSTAT
+@findex C_ESTAT
+In XCOFF files, the stab type need not indicate the section;
+@code{C_STSYM} can be used for all statics. Also, each static variable
+is enclosed in a static block. A @code{C_BSTAT} (emitted with a
+@samp{.bs} assembler directive) symbol begins the static block; its
+value is the symbol number of the csect symbol whose value is the
+address of the static block, its section is the section of the variables
+in that static block, and its name is @samp{.bs}. A @code{C_ESTAT}
+(emitted with a @samp{.es} assembler directive) symbol ends the static
+block; its name is @samp{.es} and its value and section are ignored.
+
+In ECOFF files, the storage class is used to specify the section, so the
+stab type need not indicate the section.
+
+In ELF files, for the SunPRO compiler version 2.0.1, symbol descriptor
+@samp{S} means that the address is absolute (the linker relocates it)
+and symbol descriptor @samp{V} means that the address is relative to the
+start of the relevant section for that compilation unit. SunPRO has
+plans to have the linker stop relocating stabs; I suspect that their the
+debugger gets the address from the corresponding ELF (not stab) symbol.
+I'm not sure how to find which symbol of that name is the right one.
+The clean way to do all this would be to have a the value of a symbol
+descriptor @samp{S} symbol be an offset relative to the start of the
+file, just like everything else, but that introduces obvious
+compatibility problems. For more information on linker stab relocation,
+@xref{ELF Linker Relocation}.
+
+@node Based Variables
+@section Fortran Based Variables
+
+Fortran (at least, the Sun and SGI dialects of FORTRAN-77) has a feature
+which allows allocating arrays with @code{malloc}, but which avoids
+blurring the line between arrays and pointers the way that C does. In
+stabs such a variable uses the @samp{b} symbol descriptor.
+
+For example, the Fortran declarations
+
+@example
+real foo, foo10(10), foo10_5(10,5)
+pointer (foop, foo)
+pointer (foo10p, foo10)
+pointer (foo105p, foo10_5)
+@end example
+
+produce the stabs
+
+@example
+foo:b6
+foo10:bar3;1;10;6
+foo10_5:bar3;1;5;ar3;1;10;6
+@end example
+
+In this example, @code{real} is type 6 and type 3 is an integral type
+which is the type of the subscripts of the array (probably
+@code{integer}).
+
+The @samp{b} symbol descriptor is like @samp{V} in that it denotes a
+statically allocated symbol whose scope is local to a function; see
+@xref{Statics}. The value of the symbol, instead of being the address
+of the variable itself, is the address of a pointer to that variable.
+So in the above example, the value of the @code{foo} stab is the address
+of a pointer to a real, the value of the @code{foo10} stab is the
+address of a pointer to a 10-element array of reals, and the value of
+the @code{foo10_5} stab is the address of a pointer to a 5-element array
+of 10-element arrays of reals.
+
@node Parameters
@section Parameters
-Parameters to a function are represented by a stab (or sometimes two,
-see below) for each parameter. The stabs are in the order in which the
-debugger should print the parameters (i.e., the order in which the
-parameters are declared in the source file).
+Formal parameters to a function are represented by a stab (or sometimes
+two; see below) for each parameter. The stabs are in the order in which
+the debugger should print the parameters (i.e., the order in which the
+parameters are declared in the source file). The exact form of the stab
+depends on how the parameter is being passed.
+
+@findex N_PSYM
+@findex C_PSYM
+Parameters passed on the stack use the symbol descriptor @samp{p} and
+the @code{N_PSYM} symbol type (or @code{C_PSYM} for XCOFF). The value
+of the symbol is an offset used to locate the parameter on the stack;
+its exact meaning is machine-dependent, but on most machines it is an
+offset from the frame pointer.
+
+As a simple example, the code:
+
+@example
+main (argc, argv)
+ int argc;
+ char **argv;
+@end example
+
+produces the stabs:
+
+@example
+.stabs "main:F1",36,0,0,_main # @r{36 is N_FUN}
+.stabs "argc:p1",160,0,0,68 # @r{160 is N_PSYM}
+.stabs "argv:p20=*21=*2",160,0,0,72
+@end example
+
+The type definition of @code{argv} is interesting because it contains
+several type definitions. Type 21 is pointer to type 2 (char) and
+@code{argv} (type 20) is pointer to type 21.
+
+@c FIXME: figure out what these mean and describe them coherently.
+The following symbol descriptors are also said to go with @code{N_PSYM}.
+The value of the symbol is said to be an offset from the argument
+pointer (I'm not sure whether this is true or not).
+
+@example
+pP (<<??>>)
+pF Fortran function parameter
+X (function result variable)
+@end example
+
+@menu
+* Register Parameters::
+* Local Variable Parameters::
+* Reference Parameters::
+* Conformant Arrays::
+@end menu
-The symbol descriptor @samp{p} is used to refer to parameters which are
-in the arglist. Symbols have symbol type @code{N_PSYM}. The value of
-the symbol is the offset relative to the argument list.
+@node Register Parameters
+@subsection Passing Parameters in Registers
-If the parameter is passed in a register, then the traditional way to do
-this is to provide two symbols for each argument:
+If the parameter is passed in a register, then traditionally there are
+two symbols for each argument:
@example
.stabs "arg:p1" . . . ; N_PSYM
.stabs "arg:r1" . . . ; N_RSYM
@end example
-Debuggers are expected to use the second one to find the value, and the
-first one to know that it is an argument.
+Debuggers use the second one to find the value, and the first one to
+know that it is an argument.
-Because this is kind of ugly, some compilers use symbol descriptor
-@samp{P} or @samp{R} to indicate an argument which is in a register.
-The symbol value is the register number. @samp{P} and @samp{R} mean the
-same thing, the difference is that @samp{P} is a GNU invention and
-@samp{R} is an IBM (xcoff) invention. As of version 4.9, GDB should
-handle either one. Symbol type @code{C_RPSYM} is used with @samp{R} and
-@code{N_RSYM} is used with @samp{P}.
+@findex C_RPSYM
+@findex N_RSYM, for parameters
+Because that approach is kind of ugly, some compilers use symbol
+descriptor @samp{P} or @samp{R} to indicate an argument which is in a
+register. Symbol type @code{C_RPSYM} is used in XCOFF and @code{N_RSYM}
+is used otherwise. The symbol's value is the register number. @samp{P}
+and @samp{R} mean the same thing; the difference is that @samp{P} is a
+GNU invention and @samp{R} is an IBM (XCOFF) invention. As of version
+4.9, GDB should handle either one.
-According to the AIX documentation symbol descriptor @samp{D} is for a
+There is at least one case where GCC uses a @samp{p} and @samp{r} pair
+rather than @samp{P}; this is where the argument is passed in the
+argument list and then loaded into a register.
+
+According to the AIX documentation, symbol descriptor @samp{D} is for a
parameter passed in a floating point register. This seems
unnecessary---why not just use @samp{R} with a register number which
indicates that it's a floating point register? I haven't verified
whether the system actually does what the documentation indicates.
-There is at least one case where GCC uses a @samp{p} and @samp{r} pair
-rather than @samp{P}; this is where the argument is passed in the
-argument list and then loaded into a register.
-
+@c FIXME: On the hppa this is for any type > 8 bytes, I think, and not
+@c for small structures (investigate).
On the sparc and hppa, for a @samp{P} symbol whose type is a structure
or union, the register contains the address of the structure. On the
-sparc, this is also true of a @samp{p} and @samp{r} pair (using Sun cc) or a
-@samp{p} symbol. However, if a (small) structure is really in a
-register, @samp{r} is used. And, to top it all off, on the hppa it
-might be a structure which was passed on the stack and loaded into a
-register and for which there is a @samp{p} and @samp{r} pair! I believe
-that symbol descriptor @samp{i} is supposed to deal with this case, (it
-is said to mean "value parameter by reference, indirect access", I don't
-know the source for this information) but I don't know details or what
-compilers or debuggers use it, if any (not GDB or GCC). It is not clear
-to me whether this case needs to be dealt with differently than
-parameters passed by reference (see below).
-
-There is another case similar to an argument in a register, which is an
-argument which is actually stored as a local variable. Sometimes this
+sparc, this is also true of a @samp{p} and @samp{r} pair (using Sun
+@code{cc}) or a @samp{p} symbol. However, if a (small) structure is
+really in a register, @samp{r} is used. And, to top it all off, on the
+hppa it might be a structure which was passed on the stack and loaded
+into a register and for which there is a @samp{p} and @samp{r} pair! I
+believe that symbol descriptor @samp{i} is supposed to deal with this
+case (it is said to mean "value parameter by reference, indirect
+access"; I don't know the source for this information), but I don't know
+details or what compilers or debuggers use it, if any (not GDB or GCC).
+It is not clear to me whether this case needs to be dealt with
+differently than parameters passed by reference (@pxref{Reference Parameters}).
+
+@node Local Variable Parameters
+@subsection Storing Parameters as Local Variables
+
+There is a case similar to an argument in a register, which is an
+argument that is actually stored as a local variable. Sometimes this
happens when the argument was passed in a register and then the compiler
stores it as a local variable. If possible, the compiler should claim
-that it's in a register, but this isn't always done. Some compilers use
-the pair of symbols approach described above (@samp{@var{arg}:p} followed by
-@samp{@var{arg}:}); this includes GCC1 (not GCC2) on the sparc when passing a small
-structure and GCC2 (sometimes) when the argument type is float and it is
-passed as a double and converted to float by the prologue (in the latter
-case the type of the @samp{@var{arg}:p} symbol is double and the type of the @samp{@var{arg}:}
-symbol is float). GCC, at least on the 960, uses a single @samp{p}
-symbol descriptor for an argument which is stored as a local variable
-but uses @code{N_LSYM} instead of @code{N_PSYM}. In this case the value
-of the symbol is an offset relative to the local variables for that
-function, not relative to the arguments (on some machines those are the
-same thing, but not on all).
-
-If the parameter is passed by reference (e.g., Pascal VAR parameters),
-then type symbol descriptor is @samp{v} if it is in the argument list,
-or @samp{a} if it in a register. Other than the fact that these contain
-the address of the parameter other than the parameter itself, they are
-identical to @samp{p} and @samp{R}, respectively. I believe @samp{a} is
-an AIX invention; @samp{v} is supported by all stabs-using systems as
-far as I know.
-
-@c Is this paragraph correct? It is based on piecing together patchy
-@c information and some guesswork
-Conformant arrays refer to a feature of Modula-2, and perhaps other
-languages, in which the size of an array parameter is not known to the
-called function until run-time. Such parameters have two stabs, a
-@samp{x} for the array itself, and a @samp{C}, which represents the size
-of the array. The value of the @samp{x} stab is the offset in the
-argument list where the address of the array is stored (it this right?
-it is a guess); the value of the @samp{C} stab is the offset in the
-argument list where the size of the array (in elements? in bytes?) is
-stored.
+that it's in a register, but this isn't always done.
-The following are also said to go with @code{N_PSYM}:
+If a parameter is passed as one type and converted to a smaller type by
+the prologue (for example, the parameter is declared as a @code{float},
+but the calling conventions specify that it is passed as a
+@code{double}), then GCC2 (sometimes) uses a pair of symbols. The first
+symbol uses symbol descriptor @samp{p} and the type which is passed.
+The second symbol has the type and location which the parameter actually
+has after the prologue. For example, suppose the following C code
+appears with no prototypes involved:
@example
-"name" -> "param_name:#type"
- -> pP (<<??>>)
- -> pF Fortran function parameter
- -> X (function result variable)
- -> b (based variable)
-
-value -> offset from the argument pointer (positive).
+void
+subr (f)
+ float f;
+@{
@end example
-As a simple example, the code
+if @code{f} is passed as a double at stack offset 8, and the prologue
+converts it to a float in register number 0, then the stabs look like:
@example
-main (argc, argv)
- int argc;
- char **argv;
-@{
+.stabs "f:p13",160,0,3,8 # @r{160 is @code{N_PSYM}, here 13 is @code{double}}
+.stabs "f:r12",64,0,3,0 # @r{64 is @code{N_RSYM}, here 12 is @code{float}}
@end example
-produces the stabs
+In both stabs 3 is the line number where @code{f} is declared
+(@pxref{Line Numbers}).
+
+@findex N_LSYM, for parameter
+GCC, at least on the 960, has another solution to the same problem. It
+uses a single @samp{p} symbol descriptor for an argument which is stored
+as a local variable but uses @code{N_LSYM} instead of @code{N_PSYM}. In
+this case, the value of the symbol is an offset relative to the local
+variables for that function, not relative to the arguments; on some
+machines those are the same thing, but not on all.
+
+@c This is mostly just background info; the part that logically belongs
+@c here is the last sentence.
+On the VAX or on other machines in which the calling convention includes
+the number of words of arguments actually passed, the debugger (GDB at
+least) uses the parameter symbols to keep track of whether it needs to
+print nameless arguments in addition to the formal parameters which it
+has printed because each one has a stab. For example, in
@example
-.stabs "main:F1",36,0,0,_main # @r{36 is N_FUN}
-.stabs "argc:p1",160,0,0,68 # @r{160 is N_PSYM}
-.stabs "argv:p20=*21=*2",160,0,0,72
+extern int fprintf (FILE *stream, char *format, @dots{});
+@dots{}
+fprintf (stdout, "%d\n", x);
@end example
-The type definition of argv is interesting because it contains several
-type definitions. Type 21 is pointer to type 2 (char) and argv (type 20) is
-pointer to type 21.
+there are stabs for @code{stream} and @code{format}. On most machines,
+the debugger can only print those two arguments (because it has no way
+of knowing that additional arguments were passed), but on the VAX or
+other machines with a calling convention which indicates the number of
+words of arguments, the debugger can print all three arguments. To do
+so, the parameter symbol (symbol descriptor @samp{p}) (not necessarily
+@samp{r} or symbol descriptor omitted symbols) needs to contain the
+actual type as passed (for example, @code{double} not @code{float} if it
+is passed as a double and converted to a float).
+
+@node Reference Parameters
+@subsection Passing Parameters by Reference
+
+If the parameter is passed by reference (e.g., Pascal @code{VAR}
+parameters), then the symbol descriptor is @samp{v} if it is in the
+argument list, or @samp{a} if it in a register. Other than the fact
+that these contain the address of the parameter rather than the
+parameter itself, they are identical to @samp{p} and @samp{R},
+respectively. I believe @samp{a} is an AIX invention; @samp{v} is
+supported by all stabs-using systems as far as I know.
+
+@node Conformant Arrays
+@subsection Passing Conformant Array Parameters
+
+@c Is this paragraph correct? It is based on piecing together patchy
+@c information and some guesswork
+Conformant arrays are a feature of Modula-2, and perhaps other
+languages, in which the size of an array parameter is not known to the
+called function until run-time. Such parameters have two stabs: a
+@samp{x} for the array itself, and a @samp{C}, which represents the size
+of the array. The value of the @samp{x} stab is the offset in the
+argument list where the address of the array is stored (it this right?
+it is a guess); the value of the @samp{C} stab is the offset in the
+argument list where the size of the array (in elements? in bytes?) is
+stored.
@node Types
-@chapter Defining types
+@chapter Defining Types
-Now let's look at some variable definitions involving complex types.
-This involves understanding better how types are described. In the
-examples so far types have been described as references to previously
-defined types or defined in terms of subranges of or pointers to
-previously defined types. The section that follows discusses
-the other type descriptors that may follow the @samp{=} sign in a
-type definition.
+The examples so far have described types as references to previously
+defined types, or defined in terms of subranges of or pointers to
+previously defined types. This chapter describes the other type
+descriptors that may follow the @samp{=} in a type definition.
@menu
-* Builtin types:: Integers, floating point, void, etc.
+* Builtin Types:: Integers, floating point, void, etc.
* Miscellaneous Types:: Pointers, sets, files, etc.
-* Cross-references:: Referring to a type not yet defined.
+* Cross-References:: Referring to a type not yet defined.
* Subranges:: A type with a specific range.
* Arrays:: An aggregate type of same-typed elements.
* Strings:: Like an array but also has a length.
* Function Types::
@end menu
-@node Builtin types
-@section Builtin types
+@node Builtin Types
+@section Builtin Types
Certain types are built in (@code{int}, @code{short}, @code{void},
@code{float}, etc.); the debugger recognizes these types and knows how
-to handle them. Thus don't be surprised if some of the following ways
+to handle them. Thus, don't be surprised if some of the following ways
of specifying builtin types do not specify everything that a debugger
would need to know about the type---in some cases they merely specify
enough information to distinguish the type from other types.
-The traditional way to define builtin types is convolunted, so new ways
-have been invented to describe them. Sun's ACC uses the @samp{b} and
-@samp{R} type descriptors (@pxref{Builtin Type Descriptors}), and IBM
-uses negative type numbers (@pxref{Negative Type Numbers}). GDB can
-accept all three, as of version 4.8; DBX just accepts the traditional
-builtin types and perhaps one of the other two formats.
+The traditional way to define builtin types is convoluted, so new ways
+have been invented to describe them. Sun's @code{acc} uses special
+builtin type descriptors (@samp{b} and @samp{R}), and IBM uses negative
+type numbers. GDB accepts all three ways, as of version 4.8; dbx just
+accepts the traditional builtin types and perhaps one of the other two
+formats. The following sections describe each of these formats.
@menu
-* Traditional Builtin Types:: Put on your seatbelts and prepare for kludgery
+* Traditional Builtin Types:: Put on your seat belts and prepare for kludgery
* Builtin Type Descriptors:: Builtin types with special type descriptors
* Negative Type Numbers:: Builtin types using negative type numbers
@end menu
@node Traditional Builtin Types
-@subsection Traditional Builtin types
+@subsection Traditional Builtin Types
-Often types are defined as subranges of themselves. If the array bounds
-can fit within an @code{int}, then they are given normally. For example:
+This is the traditional, convoluted method for defining builtin types.
+There are several classes of such type definitions: integer, floating
+point, and @code{void}.
+
+@menu
+* Traditional Integer Types::
+* Traditional Other Types::
+@end menu
+
+@node Traditional Integer Types
+@subsubsection Traditional Integer Types
+
+Often types are defined as subranges of themselves. If the bounding values
+fit within an @code{int}, then they are given normally. For example:
@example
.stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0 # @r{128 is N_LSYM}
.stabs "unsigned short:t6=r1;0;65535;",128,0,0,0
@end example
-If the lower bound of a subrange is 0 and the upper bound is -1, it
-means that the type is an unsigned integral type whose bounds are too
-big to describe in an int. Traditionally this is only used for
-@code{unsigned int} and @code{unsigned long}; GCC also sometimes uses it
-for @code{long long} and @code{unsigned long long}, and the only way to
-tell those types apart is to look at their names. On other machines GCC
-puts out bounds in octal, with a leading 0. In this case a negative
-bound consists of a number which is a 1 bit followed by a bunch of 0
-bits, and a positive bound is one in which a bunch of bits are 1.
+If the lower bound of a subrange is 0 and the upper bound is -1,
+the type is an unsigned integral type whose bounds are too
+big to describe in an @code{int}. Traditionally this is only used for
+@code{unsigned int} and @code{unsigned long}:
@example
.stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
-.stabs "long long int:t7=r1;0;-1;",128,0,0,0
+@end example
+
+For larger types, GCC 2.4.5 puts out bounds in octal, with one or more
+leading zeroes. In this case a negative bound consists of a number
+which is a 1 bit (for the sign bit) followed by a 0 bit for each bit in
+the number (except the sign bit), and a positive bound is one which is a
+1 bit for each bit in the number (except possibly the sign bit). All
+known versions of dbx and GDB version 4 accept this (at least in the
+sense of not refusing to process the file), but GDB 3.5 refuses to read
+the whole file containing such symbols. So GCC 2.3.3 did not output the
+proper size for these types. As an example of octal bounds, the string
+fields of the stabs for 64 bit integer types look like:
+
+@c .stabs directives, etc., omitted to make it fit on the page.
+@example
+long int:t3=r1;001000000000000000000000;000777777777777777777777;
+long unsigned int:t5=r1;000000000000000000000000;001777777777777777777777;
@end example
If the lower bound of a subrange is 0 and the upper bound is negative,
-it means that it is an unsigned integral type whose size in bytes is the
+the type is an unsigned integral type whose size in bytes is the
absolute value of the upper bound. I believe this is a Convex
convention for @code{unsigned long long}.
If the lower bound of a subrange is negative and the upper bound is 0,
-it means that the type is a signed integral type whose size in bytes is
+the type is a signed integral type whose size in bytes is
the absolute value of the lower bound. I believe this is a Convex
convention for @code{long long}. To distinguish this from a legitimate
subrange, the type should be a subrange of itself. I'm not sure whether
this is the case for Convex.
-If the upper bound of a subrange is 0, it means that this is a floating
-point type, and the lower bound of the subrange indicates the number of
-bytes in the type:
+@node Traditional Other Types
+@subsubsection Traditional Other Types
+
+If the upper bound of a subrange is 0 and the lower bound is positive,
+the type is a floating point type, and the lower bound of the subrange
+indicates the number of bytes in the type:
@example
.stabs "float:t12=r1;4;0;",128,0,0,0
@end example
However, GCC writes @code{long double} the same way it writes
-@code{double}; the only way to distinguish them is by the name:
+@code{double}, so there is no way to distinguish.
@example
.stabs "long double:t14=r1;8;0;",128,0,0,0
@end example
-Complex types are defined the same way as floating-point types; the only
-way to distinguish a single-precision complex from a double-precision
-floating-point type is by the name.
+Complex types are defined the same way as floating-point types; there is
+no way to distinguish a single-precision complex from a double-precision
+floating-point type.
The C @code{void} type is defined as itself:
I'm not sure how a boolean type is represented.
@node Builtin Type Descriptors
-@subsection Defining Builtin Types using Builtin Type Descriptors
+@subsection Defining Builtin Types Using Builtin Type Descriptors
-There are various type descriptors to define builtin types:
+This is the method used by Sun's @code{acc} for defining builtin types.
+These are the type descriptors to define builtin types:
@table @code
@c FIXME: clean up description of width and offset, once we figure out
Documented by AIX to define a wide character type, but their compiler
actually uses negative type numbers (@pxref{Negative Type Numbers}).
-@item R @var{fp_type} ; @var{bytes} ;
-Define a floating point type. @var{fp_type} has one of the following values:
+@item R @var{fp-type} ; @var{bytes} ;
+Define a floating point type. @var{fp-type} has one of the following values:
@table @code
@item 1 (NF_SINGLE)
@c "GDB source" really means @file{include/aout/stab_gnu.h}, but trying
@c to put that here got an overfull hbox.
These are for complex numbers. A comment in the GDB source describes
-them as Fortran complex, double complex, and complex*16, respectively,
-but what does that mean? (i.e., Single precision? Double precison?).
+them as Fortran @code{complex}, @code{double complex}, and
+@code{complex*16}, respectively, but what does that mean? (i.e., Single
+precision? Double precision?).
@item 6 (NF_LDOUBLE)
-Long double. This should probably only be used for Sun format long
-double, and new codes should be used for other floating point formats
-(@code{NF_DOUBLE} can be used if a long double is really just an IEEE double,
-of course).
+Long double. This should probably only be used for Sun format
+@code{long double}, and new codes should be used for other floating
+point formats (@code{NF_DOUBLE} can be used if a @code{long double} is
+really just an IEEE double, of course).
@end table
@var{bytes} is the number of bytes occupied by the type. This allows a
debugger to perform some operations with the type even if it doesn't
-understand @var{fp_code}.
+understand @var{fp-type}.
@item g @var{type-information} ; @var{nbits}
Documented by AIX to define a floating type, but their compiler actually
I'm not sure how a boolean type is represented.
@node Negative Type Numbers
-@subsection Negative Type numbers
+@subsection Negative Type Numbers
+This is the method used in XCOFF for defining builtin types.
Since the debugger knows about the builtin types anyway, the idea of
negative type numbers is simply to give a special type number which
-indicates the built in type. There is no stab defining these types.
-
-I'm not sure whether anyone has tried to define what this means if
-@code{int} can be other than 32 bits (or other types can be other than
-their customary size). If @code{int} has exactly one size for each
-architecture, then it can be handled easily enough, but if the size of
-@code{int} can vary according the compiler options, then it gets hairy.
-The best way to do this would be to define separate negative type
-numbers for 16-bit @code{int} and 32-bit @code{int}; therefore I have
-indicated below the customary size (and other format information) for
-each type. The information below is currently correct because AIX on
-the RS6000 is the only system which uses these type numbers. If these
-type numbers start to get used on other systems, I suspect the correct
-thing to do is to define a new number in cases where a type does not
-have the size and format indicated below (or avoid negative type numbers
-in these cases).
-
-Also note that part of the definition of the negative type number is
-the name of the type. Types with identical size and format but
-different names have different negative type numbers.
+indicates the builtin type. There is no stab defining these types.
+
+There are several subtle issues with negative type numbers.
+
+One is the size of the type. A builtin type (for example the C types
+@code{int} or @code{long}) might have different sizes depending on
+compiler options, the target architecture, the ABI, etc. This issue
+doesn't come up for IBM tools since (so far) they just target the
+RS/6000; the sizes indicated below for each size are what the IBM
+RS/6000 tools use. To deal with differing sizes, either define separate
+negative type numbers for each size (which works but requires changing
+the debugger, and, unless you get both AIX dbx and GDB to accept the
+change, introduces an incompatibility), or use a type attribute
+(@pxref{String Field}) to define a new type with the appropriate size
+(which merely requires a debugger which understands type attributes,
+like AIX dbx or GDB). For example,
+
+@example
+.stabs "boolean:t10=@@s8;-16",128,0,0,0
+@end example
+
+defines an 8-bit boolean type, and
+
+@example
+.stabs "boolean:t10=@@s64;-16",128,0,0,0
+@end example
+
+defines a 64-bit boolean type.
+
+A similar issue is the format of the type. This comes up most often for
+floating-point types, which could have various formats (particularly
+extended doubles, which vary quite a bit even among IEEE systems).
+Again, it is best to define a new negative type number for each
+different format; changing the format based on the target system has
+various problems. One such problem is that the Alpha has both VAX and
+IEEE floating types. One can easily imagine one library using the VAX
+types and another library in the same executable using the IEEE types.
+Another example is that the interpretation of whether a boolean is true
+or false can be based on the least significant bit, most significant
+bit, whether it is zero, etc., and different compilers (or different
+options to the same compiler) might provide different kinds of boolean.
+
+The last major issue is the names of the types. The name of a given
+type depends @emph{only} on the negative type number given; these do not
+vary depending on the language, the target system, or anything else.
+One can always define separate type numbers---in the following list you
+will see for example separate @code{int} and @code{integer*4} types
+which are identical except for the name. But compatibility can be
+maintained by not inventing new negative type numbers and instead just
+defining a new type with a new name. For example:
+
+@example
+.stabs "CARDINAL:t10=-8",128,0,0,0
+@end example
+
+Here is the list of negative type numbers. The phrase @dfn{integral
+type} is used to mean twos-complement (I strongly suspect that all
+machines which use stabs use twos-complement; most machines use
+twos-complement these days).
@table @code
@item -1
@code{int}, 32 bit signed integral type.
@item -2
-@code{char}, 8 bit type holding a character. Both GDB and DBX on AIX
+@code{char}, 8 bit type holding a character. Both GDB and dbx on AIX
treat this as signed. GCC uses this type whether @code{char} is signed
-or not, which seems like a bad idea. The AIX compiler (xlc) seems to
+or not, which seems like a bad idea. The AIX compiler (@code{xlc}) seems to
avoid this type; it uses -5 instead for @code{char}.
@item -3
@code{integer}. 32 bit signed integral type.
@item -16
-@code{boolean}. 32 bit type. How is the truth value encoded? Is it
-the least significant bit or is it a question of whether the whole value
-is zero or non-zero?
+@code{boolean}. 32 bit type. GDB and GCC assume that zero is false,
+one is true, and other values have unspecified meaning. I hope this
+agrees with how the IBM tools use the type.
@item -17
@code{short real}. IEEE single precision.
@item -30
@code{wchar}. Wide character, 16 bits wide, unsigned (what format?
Unicode?).
+
+@item -31
+@code{long long}, 64 bit signed integral type.
+
+@item -32
+@code{unsigned long long}, 64 bit unsigned integral type.
+
+@item -33
+@code{logical*8}, 64 bit unsigned integral type.
+
+@item -34
+@code{integer*8}, 64 bit signed integral type.
@end table
@node Miscellaneous Types
@item b @var{type-information} ; @var{bytes}
Pascal space type. This is documented by IBM; what does it mean?
-Note that this use of the @samp{b} type descriptor can be distinguished
+This use of the @samp{b} type descriptor can be distinguished
from its use for builtin integral types (@pxref{Builtin Type
Descriptors}) because the character following the type descriptor is
always a digit, @samp{(}, or @samp{-}.
@item B @var{type-information}
-A volatile-qualified version of @var{type-information}. This is a Sun
-extension. A volatile-qualified type means that references and stores
-to a variable of that type must not be optimized or cached; they must
-occur as the user specifies them.
+A volatile-qualified version of @var{type-information}. This is
+a Sun extension. References and stores to a variable with a
+volatile-qualified type must not be optimized or cached; they
+must occur as the user specifies them.
@item d @var{type-information}
File of type @var{type-information}. As far as I know this is only used
@item k @var{type-information}
A const-qualified version of @var{type-information}. This is a Sun
-extension. A const-qualified type means that a variable of this type
-cannot be modified.
+extension. A variable with a const-qualified type cannot be modified.
@item M @var{type-information} ; @var{length}
Multiple instance type. The type seems to composed of @var{length}
enumeration or a subrange, and the type is a bitmask whose length is
specified by the number of elements in @var{type-information}.
+In CHILL, @c OBSOLETE
+if it is a bitstring instead of a set, also use the @samp{S}
+type attribute (@pxref{String Field}).
+
@item * @var{type-information}
Pointer to @var{type-information}.
@end table
-@node Cross-references
-@section Cross-references to other types
+@node Cross-References
+@section Cross-References to Other Types
-If a type is used before it is defined, one common way to deal with this
-is just to use a type reference to a type which has not yet been
-defined. The debugger is expected to be able to deal with this.
+A type can be used before it is defined; one common way to deal with
+that situation is just to use a type reference to a type which has not
+yet been defined.
Another way is with the @samp{x} type descriptor, which is followed by
@samp{s} for a structure tag, @samp{u} for a union tag, or @samp{e} for
a enumerator tag, followed by the name of the tag, followed by @samp{:}.
-for example the following C declarations:
+If the name contains @samp{::} between a @samp{<} and @samp{>} pair (for
+C++ templates), such a @samp{::} does not end the name---only a single
+@samp{:} ends the name; see @ref{Nested Symbols}.
+
+For example, the following C declarations:
@example
struct foo;
struct foo *bar;
@end example
-produce
+@noindent
+produce:
@example
.stabs "bar:G16=*17=xsfoo:",32,0,0,0
descriptor, which is followed by the name of the module from which the
type is imported, followed by @samp{:}, followed by the name of the
type. There is then optionally a comma followed by type information for
-the type (This differs from merely naming the type (@pxref{Typedefs}) in
+the type. This differs from merely naming the type (@pxref{Typedefs}) in
that it identifies the module; I don't understand whether the name of
the type given here is always just the same as the name we are giving
it, or whether this type descriptor is used with a nameless stab
-(@pxref{Stabs Format}), or what). The symbol ends with @samp{;}.
+(@pxref{String Field}), or what. The symbol ends with @samp{;}.
@node Subranges
-@section Subrange types
+@section Subrange Types
The @samp{r} type descriptor defines a type as a subrange of another
-type. It is followed by type information for the type which it is a
-subrange of, a semicolon, an integral lower bound, a semicolon, an
+type. It is followed by type information for the type of which it is a
+subrange, a semicolon, an integral lower bound, a semicolon, an
integral upper bound, and a semicolon. The AIX documentation does not
specify the trailing semicolon, in an effort to specify array indexes
more cleanly, but a subrange which is not an array index has always
the argument list.
@item a @var{register-number}
-The bound is pased by reference in register number
+The bound is passed by reference in register number
@var{register-number}.
@item t @var{register-number}
Subranges are also used for builtin types; see @ref{Traditional Builtin Types}.
@node Arrays
-@section Array types
+@section Array Types
Arrays use the @samp{a} type descriptor. Following the type descriptor
is the type of the index and the type of the array elements. If the
-index type is a range type, it will end in a semicolon; if it is not a
-range type (for example, if it is a type reference), there does not
+index type is a range type, it ends in a semicolon; otherwise
+(for example, if it is a type reference), there does not
appear to be any way to tell where the types are separated. In an
effort to clean up this mess, IBM documents the two types as being
separated by a semicolon, and a range type as not ending in a semicolon
It is well established, and widely used, that the type of the index,
unlike most types found in the stabs, is merely a type definition, not
-type information (@pxref{Stabs Format}) (that is, it need not start with
-@var{type-number}@code{=} if it is defining a new type). According to a
+type information (@pxref{String Field}) (that is, it need not start with
+@samp{@var{type-number}=} if it is defining a new type). According to a
comment in GDB, this is also true of the type of the array elements; it
gives @samp{ar1;1;10;ar1;1;10;4} as a legitimate way to express a two
dimensional array. According to AIX documentation, the element type
must be type information. GDB accepts either.
-The type of the index is often a range type, expressed as the letter r
-and some parameters. It defines the size of the array. In the example
-below, the range @code{r1;0;2;} defines an index type which is a
-subrange of type 1 (integer), with a lower bound of 0 and an upper bound
-of 2. This defines the valid range of subscripts of a three-element C
-array.
+The type of the index is often a range type, expressed as the type
+descriptor @samp{r} and some parameters. It defines the size of the
+array. In the example below, the range @samp{r1;0;2;} defines an index
+type which is a subrange of type 1 (integer), with a lower bound of 0
+and an upper bound of 2. This defines the valid range of subscripts of
+a three-element C array.
-For example, the definition
+For example, the definition:
@example
char char_vec[3] = @{'a','b','c'@};
@end example
@noindent
-produces the output
+produces the output:
@example
.stabs "char_vec:G19=ar1;0;2;2",32,0,0,0
.byte 99
@end example
-If an array is @dfn{packed}, it means that the elements are spaced more
+If an array is @dfn{packed}, the elements are spaced more
closely than normal, saving memory at the expense of speed. For
example, an array of 3-byte objects might, if unpacked, have each
element aligned on a 4-byte boundary, but if packed, have no padding.
One way to specify that something is packed is with type attributes
-(@pxref{Stabs Format}), in the case of arrays another is to use the
+(@pxref{String Field}). In the case of arrays, another is to use the
@samp{P} type descriptor instead of @samp{a}. Other than specifying a
packed array, @samp{P} is identical to @samp{a}.
Pascal Stringptr. What is this? This is an AIX feature.
@end table
+Languages, such as CHILL @c OBSOLETE
+which have a string type which is basically
+just an array of characters use the @samp{S} type attribute
+(@pxref{String Field}).
+
@node Enumerations
@section Enumerations
@c FIXME: Where does this information properly go? Perhaps it is
@c redundant with something we already explain.
-The source line below declares an enumeration type. It is defined at
-file scope between the bodies of main and s_proc in example2.c.
+The source line below declares an enumeration type at file scope.
The type definition is located after the @code{N_RBRAC} that marks the end of
the previous procedure's block scope, and before the @code{N_FUN} that marks
the beginning of the next procedure's block scope. Therefore it does not
@end example
@noindent
-generates the following stab
+generates the following stab:
@example
.stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0
@end example
-The symbol descriptor (T) says that the stab describes a structure,
-enumeration, or type tag. The type descriptor e, following the 22= of
-the type definition narrows it down to an enumeration type. Following
-the e is a list of the elements of the enumeration. The format is
-name:value,. The list of elements ends with a ;.
+The symbol descriptor (@samp{T}) says that the stab describes a
+structure, enumeration, or union tag. The type descriptor @samp{e},
+following the @samp{22=} of the type definition narrows it down to an
+enumeration type. Following the @samp{e} is a list of the elements of
+the enumeration. The format is @samp{@var{name}:@var{value},}. The
+list of elements ends with @samp{;}. The fact that @var{value} is
+specified as an integer can cause problems if the value is large. GCC
+2.5.2 tries to output it in octal in that case with a leading zero,
+which is probably a good thing, although GDB 4.11 supports octal only in
+cases where decimal is perfectly good. Negative decimal values are
+supported by both GDB and dbx.
There is no standard way to specify the size of an enumeration type; it
is determined by the architecture (normally all enumerations types are
-32 bits). There should be a way to specify an enumeration type of
-another size; type attributes would be one way to do this @xref{Stabs
-Format}.
+32 bits). Type attributes can be used to specify an enumeration type of
+another size for debuggers which support them; see @ref{String Field}.
+
+Enumeration types are unusual in that they define symbols for the
+enumeration values (@code{first}, @code{second}, and @code{third} in the
+above example), and even though these symbols are visible in the file as
+a whole (rather than being in a more local namespace like structure
+member names), they are defined in the type definition for the
+enumeration type rather than each having their own symbol. In order to
+be fast, GDB will only get symbols from such types (in its initial scan
+of the stabs) if the type is the first thing defined after a @samp{T} or
+@samp{t} symbol descriptor (the above example fulfills this
+requirement). If the type does not have a name, the compiler should
+emit it in a nameless stab (@pxref{String Field}); GCC does this.
@node Structures
@section Structures
-@table @strong
-@item Directive:
-@code{.stabs}
-@item Type:
-@code{N_LSYM} or @code{C_DECL}
-@item Symbol Descriptor:
-@code{T}
-@item Type Descriptor:
-@code{s}
-@end table
+The encoding of structures in stabs can be shown with an example.
The following source code declares a structure tag and defines an
-instance of the structure in global scope. Then a typedef equates the
-structure tag with a new type. A seperate stab is generated for the
-structure tag, the structure typedef, and the structure instance. The
-stabs for the tag and the typedef are emited when the definitions are
+instance of the structure in global scope. Then a @code{typedef} equates the
+structure tag with a new type. Separate stabs are generated for the
+structure tag, the structure @code{typedef}, and the structure instance. The
+stabs for the tag and the @code{typedef} are emitted when the definitions are
encountered. Since the structure elements are not initialized, the
stab and code for the structure variable itself is located at the end
-of the program in .common.
+of the program in the bss section.
@example
-6 struct s_tag @{
-7 int s_int;
-8 float s_float;
-9 char s_char_vec[8];
-10 struct s_tag* s_next;
-11 @} g_an_s;
-12
-13 typedef struct s_tag s_typedef;
-@end example
+struct s_tag @{
+ int s_int;
+ float s_float;
+ char s_char_vec[8];
+ struct s_tag* s_next;
+@} g_an_s;
-The structure tag is an @code{N_LSYM} stab type because, like the enum, the
-symbol is file scope. Like the enum, the symbol descriptor is T, for
-enumeration, struct or tag type. The symbol descriptor s following
-the 16= of the type definition narrows the symbol type to struct.
+typedef struct s_tag s_typedef;
+@end example
-Following the struct symbol descriptor is the number of bytes the
-struct occupies, followed by a description of each structure element.
-The structure element descriptions are of the form name:type, bit
-offset from the start of the struct, and number of bits in the
-element.
+The structure tag has an @code{N_LSYM} stab type because, like the
+enumeration, the symbol has file scope. Like the enumeration, the
+symbol descriptor is @samp{T}, for enumeration, structure, or tag type.
+The type descriptor @samp{s} following the @samp{16=} of the type
+definition narrows the symbol type to structure.
+Following the @samp{s} type descriptor is the number of bytes the
+structure occupies, followed by a description of each structure element.
+The structure element descriptions are of the form @var{name:type, bit
+offset from the start of the struct, number of bits in the element}.
+@c FIXME: phony line break. Can probably be fixed by using an example
+@c with fewer fields.
@example
- <128> N_LSYM - type definition
- .stabs "name:sym_desc(struct tag) Type_def(16)=type_desc(struct type)
- struct_bytes
- elem_name:type_ref(int),bit_offset,field_bits;
- elem_name:type_ref(float),bit_offset,field_bits;
- elem_name:type_def(17)=type_desc(array)
- index_type(range of int from 0 to 7);
- element_type(char),bit_offset,field_bits;;",
- N_LSYM,NIL,NIL,NIL
-
-30 .stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;
- s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0
+# @r{128 is N_LSYM}
+.stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;
+ s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0
@end example
-In this example, two of the structure elements are previously defined
-types. For these, the type following the name: part of the element
-description is a simple type reference. The other two structure
+In this example, the first two structure elements are previously defined
+types. For these, the type following the @samp{@var{name}:} part of the
+element description is a simple type reference. The other two structure
elements are new types. In this case there is a type definition
-embedded after the name:. The type definition for the array element
-looks just like a type definition for a standalone array. The s_next
-field is a pointer to the same kind of structure that the field is an
-element of. So the definition of structure type 16 contains an type
-definition for an element which is a pointer to type 16.
+embedded after the @samp{@var{name}:}. The type definition for the
+array element looks just like a type definition for a stand-alone array.
+The @code{s_next} field is a pointer to the same kind of structure that
+the field is an element of. So the definition of structure type 16
+contains a type definition for an element which is a pointer to type 16.
+
+If a field is a static member (this is a C++ feature in which a single
+variable appears to be a field of every structure of a given type) it
+still starts out with the field name, a colon, and the type, but then
+instead of a comma, bit position, comma, and bit size, there is a colon
+followed by the name of the variable which each such field refers to.
+
+If the structure has methods (a C++ feature), they follow the non-method
+fields; see @ref{Cplusplus}.
@node Typedefs
@section Giving a Type a Name
+@findex N_LSYM, for types
+@findex C_DECL, for types
To give a type a name, use the @samp{t} symbol descriptor. The type
-specified by the type information (@pxref{Stabs Format}) for the stab.
+is specified by the type information (@pxref{String Field}) for the stab.
For example,
@example
-.stabs "s_typedef:t16",128,0,0,0
+.stabs "s_typedef:t16",128,0,0,0 # @r{128 is N_LSYM}
@end example
specifies that @code{s_typedef} refers to type number 16. Such stabs
-have symbol type @code{N_LSYM} or @code{C_DECL}.
+have symbol type @code{N_LSYM} (or @code{C_DECL} for XCOFF). (The Sun
+documentation mentions using @code{N_GSYM} in some cases).
-If instead, you are specifying the tag name for a structure, union, or
+If you are specifying the tag name for a structure, union, or
enumeration, use the @samp{T} symbol descriptor instead. I believe C is
the only language with this feature.
AIX provides a type descriptor to specify it. The type descriptor is
@samp{o} and is followed by a name. I don't know what the name
means---is it always the same as the name of the type, or is this type
-descriptor used with a nameless stab (@pxref{Stabs Format})? There
+descriptor used with a nameless stab (@pxref{String Field})? There
optionally follows a comma followed by type information which defines
the type of this type. If omitted, a semicolon is used in place of the
comma and the type information, and the type is much like a generic
@node Unions
@section Unions
-Next let's look at unions. In example2 this union type is declared
-locally to a procedure and an instance of the union is defined.
-
@example
-36 union u_tag @{
-37 int u_int;
-38 float u_float;
-39 char* u_char;
-40 @} an_u;
+union u_tag @{
+ int u_int;
+ float u_float;
+ char* u_char;
+@} an_u;
@end example
-This code generates a stab for the union tag and a stab for the union
-variable. Both use the @code{N_LSYM} stab type. Since the union variable is
+This code generates a stab for a union tag and a stab for a union
+variable. Both use the @code{N_LSYM} stab type. If a union variable is
scoped locally to the procedure in which it is defined, its stab is
located immediately preceding the @code{N_LBRAC} for the procedure's block
start.
-The stab for the union tag, however is located preceding the code for
+The stab for the union tag, however, is located preceding the code for
the procedure in which it is defined. The stab type is @code{N_LSYM}. This
would seem to imply that the union type is file scope, like the struct
-type s_tag. This is not true. The contents and position of the stab
-for u_type do not convey any infomation about its procedure local
+type @code{s_tag}. This is not true. The contents and position of the stab
+for @code{u_type} do not convey any information about its procedure local
scope.
-@display
- <128> N_LSYM - type
- .stabs "name:sym_desc(union tag)type_def(22)=type_desc(union)
- byte_size(4)
- elem_name:type_ref(int),bit_offset(0),bit_size(32);
- elem_name:type_ref(float),bit_offset(0),bit_size(32);
- elem_name:type_ref(ptr to char),bit_offset(0),bit_size(32);;"
- N_LSYM, NIL, NIL, NIL
-@end display
-
+@c FIXME: phony line break. Can probably be fixed by using an example
+@c with fewer fields.
@smallexample
-105 .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
- 128,0,0,0
+# @r{128 is N_LSYM}
+.stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
+ 128,0,0,0
@end smallexample
-The symbol descriptor, T, following the name: means that the stab
-describes an enumeration, struct or type tag. The type descriptor u,
-following the 23= of the type definition, narrows it down to a union
-type definition. Following the u is the number of bytes in the union.
-After that is a list of union element descriptions. Their format is
-name:type, bit offset into the union, and number of bytes for the
-element;.
-
-The stab for the union variable follows.
+The symbol descriptor @samp{T}, following the @samp{name:} means that
+the stab describes an enumeration, structure, or union tag. The type
+descriptor @samp{u}, following the @samp{23=} of the type definition,
+narrows it down to a union type definition. Following the @samp{u} is
+the number of bytes in the union. After that is a list of union element
+descriptions. Their format is @var{name:type, bit offset into the
+union, number of bytes for the element;}.
-@display
- <128> N_LSYM - local variable (with no symbol descriptor)
- .stabs "name:type_ref(u_tag)", N_LSYM, NIL, NIL, frame_ptr_offset
-@end display
+The stab for the union variable is:
@example
-130 .stabs "an_u:23",128,0,0,-20
+.stabs "an_u:23",128,0,0,-20 # @r{128 is N_LSYM}
@end example
+@samp{-20} specifies where the variable is stored (@pxref{Stack
+Variables}).
+
@node Function Types
-@section Function types
+@section Function Types
-There are various types for function variables. These types are not
-used in defining functions; see symbol descriptor @samp{f}; they are
-used for things like pointers to functions.
+Various types can be defined for function variables. These types are
+not used in defining functions (@pxref{Procedures}); they are used for
+things like pointers to functions.
The simple, traditional, type is type descriptor @samp{f} is followed by
type information for the return type of the function, followed by a
semicolon.
-This does not deal with functions the number and type of whose
-parameters are part of their type, as found in Modula-2 or ANSI C. AIX
-provides extensions to specify these, using the @samp{f}, @samp{F},
-@samp{p}, and @samp{R} type descriptors.
-
-First comes the type descriptor. Then, if it is @samp{f} or @samp{F},
-this is a function, and the type information for the return type of the
-function follows, followed by a comma. Then comes the number of
-parameters to the function and a semicolon. Then, for each parameter,
-there is the name of the parameter followed by a colon (this is only
-present for type descriptors @samp{R} and @samp{F} which represent
-Pascal function or procedure parameters), type information for the
-parameter, a comma, @samp{0} if passed by reference or @samp{1} if
-passed by value, and a semicolon. The type definition ends with a
+This does not deal with functions for which the number and types of the
+parameters are part of the type, as in Modula-2 or ANSI C. AIX provides
+extensions to specify these, using the @samp{f}, @samp{F}, @samp{p}, and
+@samp{R} type descriptors.
+
+First comes the type descriptor. If it is @samp{f} or @samp{F}, this
+type involves a function rather than a procedure, and the type
+information for the return type of the function follows, followed by a
+comma. Then comes the number of parameters to the function and a
+semicolon. Then, for each parameter, there is the name of the parameter
+followed by a colon (this is only present for type descriptors @samp{R}
+and @samp{F} which represent Pascal function or procedure parameters),
+type information for the parameter, a comma, 0 if passed by reference or
+1 if passed by value, and a semicolon. The type definition ends with a
semicolon.
-For example,
+For example, this variable definition:
@example
int (*g_pf)();
@end example
The variable defines a new type, 24, which is a pointer to another new
-type, 25, which is defined as a function returning int.
+type, 25, which is a function returning @code{int}.
@node Symbol Tables
-@chapter Symbol information in symbol tables
+@chapter Symbol Information in Symbol Tables
This chapter describes the format of symbol table entries
and how stab assembler directives map to them. It also describes the
transformations that the assembler and linker make on data from stabs.
-Each time the assembler encounters a stab in its input file it puts
-each field of the stab into corresponding fields in a symbol table
+@menu
+* Symbol Table Format::
+* Transformations On Symbol Tables::
+@end menu
+
+@node Symbol Table Format
+@section Symbol Table Format
+
+Each time the assembler encounters a stab directive, it puts
+each field of the stab into a corresponding field in a symbol table
entry of its output file. If the stab contains a string field, the
symbol table entry for that stab points to a string table entry
containing the string data from the stab. Assembler labels become
relocatable addresses. Symbol table entries in a.out have the format:
+@c FIXME: should refer to external, not internal.
@example
struct internal_nlist @{
unsigned long n_strx; /* index into string table of name */
@};
@end example
-For @code{.stabs} directives, the @code{n_strx} field holds the character offset
-from the start of the string table to the string table entry
-containing the @var{string} field. For other classes of stabs (@code{.stabn} and
-@code{.stabd}) this field is null.
+If the stab has a string, the @code{n_strx} field holds the offset in
+bytes of the string within the string table. The string is terminated
+by a NUL character. If the stab lacks a string (for example, it was
+produced by a @code{.stabn} or @code{.stabd} directive), the
+@code{n_strx} field is zero.
-Symbol table entries with @code{n_type} fields containing a value greater or
-equal to 0x20 originated as stabs generated by the compiler (with one
-random exception). Those with n_type values less than 0x20 were
-placed in the symbol table of the executable by the assembler or the
-linker.
+Symbol table entries with @code{n_type} field values greater than 0x1f
+originated as stabs generated by the compiler (with one random
+exception). The other entries were placed in the symbol table of the
+executable by the assembler or the linker.
+
+@node Transformations On Symbol Tables
+@section Transformations on Symbol Tables
The linker concatenates object files and does fixups of externally
-defined symbols. You can see the transformations made on stab data by
-the assembler and linker by examining the symbol table after each pass
-of the build, first the assemble and then the link.
+defined symbols.
-To do this, use @samp{nm -ap}. This dumps the symbol table, including
+You can see the transformations made on stab data by the assembler and
+linker by examining the symbol table after each pass of the build. To
+do this, use @samp{nm -ap}, which dumps the symbol table, including
debugging information, unsorted. For stab entries the columns are:
@var{value}, @var{other}, @var{desc}, @var{type}, @var{string}. For
assembler and linker symbols, the columns are: @var{value}, @var{type},
@var{string}.
-There are a few important things to notice about symbol tables. Where
-the value field of a stab contains a frame pointer offset, or a
-register number, that value is unchanged by the rest of the build.
+The low 5 bits of the stab type tell the linker how to relocate the
+value of the stab. Thus for stab types like @code{N_RSYM} and
+@code{N_LSYM}, where the value is an offset or a register number, the
+low 5 bits are @code{N_ABS}, which tells the linker not to relocate the
+value.
-Where the value field of a stab contains an assembly language label,
+Where the value of a stab contains an assembly language label,
it is transformed by each build step. The assembler turns it into a
relocatable address and the linker turns it into an absolute address.
+
+@menu
+* Transformations On Static Variables::
+* Transformations On Global Variables::
+* Stab Section Transformations:: For some object file formats,
+ things are a bit different.
+@end menu
+
+@node Transformations On Static Variables
+@subsection Transformations on Static Variables
+
This source line defines a static variable at file scope:
@example
-3 static int s_g_repeat
+static int s_g_repeat
@end example
@noindent
The following stab describes the symbol:
@example
-26 .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat
+.stabs "s_g_repeat:S1",38,0,0,_s_g_repeat
@end example
@noindent
@file{.o} file. The location is expressed as a data segment offset.
@example
-21 00000084 - 00 0000 STSYM s_g_repeat:S1
+00000084 - 00 0000 STSYM s_g_repeat:S1
@end example
@noindent
-in the symbol table entry from the executable, the linker has made the
+In the symbol table entry from the executable, the linker has made the
relocatable address absolute.
@example
-22 0000e00c - 00 0000 STSYM s_g_repeat:S1
+0000e00c - 00 0000 STSYM s_g_repeat:S1
@end example
+@node Transformations On Global Variables
+@subsection Transformations on Global Variables
+
Stabs for global variables do not contain location information. In
-this case the debugger finds location information in the assembler or
+this case, the debugger finds location information in the assembler or
linker symbol table entry describing the variable. The source line:
@example
-1 char g_foo = 'c';
+char g_foo = 'c';
@end example
@noindent
generates the stab:
@example
-21 .stabs "g_foo:G2",32,0,0,0
+.stabs "g_foo:G2",32,0,0,0
@end example
-The variable is represented by the following two symbol table entries
-in the object file. The first one originated as a stab. The second
-one is an external symbol. The upper case D signifies that the @code{n_type}
-field of the symbol table contains 7, @code{N_DATA} with local linkage.
-The value field following the file's line number is empty
-for the stab entry. For the linker symbol it contains the
-relocatable address corresponding to the variable.
+The variable is represented by two symbol table entries in the object
+file (see below). The first one originated as a stab. The second one
+is an external symbol. The upper case @samp{D} signifies that the
+@code{n_type} field of the symbol table contains 7, @code{N_DATA} with
+local linkage. The stab's value is zero since the value is not used for
+@code{N_GSYM} stabs. The value of the linker symbol is the relocatable
+address corresponding to the variable.
@example
-19 00000000 - 00 0000 GSYM g_foo:G2
-20 00000080 D _g_foo
+00000000 - 00 0000 GSYM g_foo:G2
+00000080 D _g_foo
@end example
@noindent
These entries as transformed by the linker. The linker symbol table
-entry now holds an absolute address.
+entry now holds an absolute address:
+
+@example
+00000000 - 00 0000 GSYM g_foo:G2
+@dots{}
+0000e008 D _g_foo
+@end example
+
+@node Stab Section Transformations
+@subsection Transformations of Stabs in separate sections
+
+For object file formats using stabs in separate sections (@pxref{Stab
+Sections}), use @code{objdump --stabs} instead of @code{nm} to show the
+stabs in an object or executable file. @code{objdump} is a GNU utility;
+Sun does not provide any equivalent.
+
+The following example is for a stab whose value is an address is
+relative to the compilation unit (@pxref{ELF Linker Relocation}). For
+example, if the source line
@example
-21 00000000 - 00 0000 GSYM g_foo:G2
+static int ld = 5;
+@end example
+
+appears within a function, then the assembly language output from the
+compiler contains:
+
+@example
+.Ddata.data:
@dots{}
-215 0000e008 D _g_foo
+ .stabs "ld:V(0,3)",0x26,0,4,.L18-Ddata.data # @r{0x26 is N_STSYM}
+@dots{}
+.L18:
+ .align 4
+ .word 0x5
+@end example
+
+Because the value is formed by subtracting one symbol from another, the
+value is absolute, not relocatable, and so the object file contains
+
+@example
+Symnum n_type n_othr n_desc n_value n_strx String
+31 STSYM 0 4 00000004 680 ld:V(0,3)
+@end example
+
+without any relocations, and the executable file also contains
+
+@example
+Symnum n_type n_othr n_desc n_value n_strx String
+31 STSYM 0 4 00000004 680 ld:V(0,3)
@end example
@node Cplusplus
-@chapter GNU C++ stabs
+@chapter GNU C++ Stabs
@menu
-* Basic Cplusplus types::
-* Simple classes::
-* Class instance::
+* Class Names:: C++ class names are both tags and typedefs.
+* Nested Symbols:: C++ symbol names can be within other types.
+* Basic Cplusplus Types::
+* Simple Classes::
+* Class Instance::
* Methods:: Method definition
+* Method Type Descriptor:: The @samp{#} type descriptor
+* Member Type Descriptor:: The @samp{@@} type descriptor
* Protections::
* Method Modifiers::
* Virtual Methods::
-* Inheritence::
+* Inheritance::
* Virtual Base Classes::
* Static Members::
@end menu
-Type descriptors added for C++ descriptions:
+@node Class Names
+@section C++ Class Names
-@table @code
-@item #
-method type (@code{##} if minimal debug)
+In C++, a class name which is declared with @code{class}, @code{struct},
+or @code{union}, is not only a tag, as in C, but also a type name. Thus
+there should be stabs with both @samp{t} and @samp{T} symbol descriptors
+(@pxref{Typedefs}).
-@item @@
-Member (class and variable) type. It is followed by type information
-for the offset basetype, a comma, and type information for the type of
-the field being pointed to. (FIXME: this is acknowledged to be
-gibberish. Can anyone say what really goes here?).
+To save space, there is a special abbreviation for this case. If the
+@samp{T} symbol descriptor is followed by @samp{t}, then the stab
+defines both a type name and a tag.
-Note that there is a conflict between this and type attributes
-(@pxref{Stabs Format}); both use type descriptor @samp{@@}.
-Fortunately, the @samp{@@} type descriptor used in this C++ sense always
-will be followed by a digit, @samp{(}, or @samp{-}, and type attributes
-never start with those things.
-@end table
+For example, the C++ code
+
+@example
+struct foo @{int x;@};
+@end example
+
+can be represented as either
-@node Basic Cplusplus types
-@section Basic types for C++
+@example
+.stabs "foo:T19=s4x:1,0,32;;",128,0,0,0 # @r{128 is N_LSYM}
+.stabs "foo:t19",128,0,0,0
+@end example
+
+or
+
+@example
+.stabs "foo:Tt19=s4x:1,0,32;;",128,0,0,0
+@end example
+
+@node Nested Symbols
+@section Defining a Symbol Within Another Type
+
+In C++, a symbol (such as a type name) can be defined within another type.
+@c FIXME: Needs example.
+
+In stabs, this is sometimes represented by making the name of a symbol
+which contains @samp{::}. Such a pair of colons does not end the name
+of the symbol, the way a single colon would (@pxref{String Field}). I'm
+not sure how consistently used or well thought out this mechanism is.
+So that a pair of colons in this position always has this meaning,
+@samp{:} cannot be used as a symbol descriptor.
+
+For example, if the string for a stab is @samp{foo::bar::baz:t5=*6},
+then @code{foo::bar::baz} is the name of the symbol, @samp{t} is the
+symbol descriptor, and @samp{5=*6} is the type information.
+
+@node Basic Cplusplus Types
+@section Basic Types For C++
<< the examples that follow are based on a01.C >>
.stabs "$vtbl_ptr_type:T17",128,0,0,0
@end example
-@node Simple classes
-@section Simple class definition
+@node Simple Classes
+@section Simple Class Definition
The stabs describing C++ language features are an extension of the
stabs describing C. Stabs representing C++ class types elaborate
The class @code{baseA} is represented by two stabs. The first stab describes
the class as a structure type. The second stab describes a structure
tag of the class type. Both stabs are of stab type @code{N_LSYM}. Since the
-stab is not located between an @code{N_FUN} and a @code{N_LBRAC} stab this indicates
+stab is not located between an @code{N_FUN} and an @code{N_LBRAC} stab this indicates
that the class is defined at file scope. If it were, then the @code{N_LSYM}
would signify a local variable.
A stab describing a C++ class type is similar in format to a stab
describing a C struct, with each class member shown as a field in the
structure. The part of the struct format describing fields is
-expanded to include extra information relevent to C++ class members.
+expanded to include extra information relevant to C++ class members.
In addition, if the class has multiple base classes or virtual
functions the struct format outside of the field parts is also
augmented.
method, and the type number of the first base class defining the
method.
-When the field name is a method name it is followed by two colons
-rather than one. This is followed by a new type definition for the
-method. This is a number followed by an equal sign and then the
-symbol descriptor @samp{##}, indicating a method type. This is followed by
-a type reference showing the return type of the method and a
-semi-colon.
-
-The format of an overloaded operator method name differs from that
-of other methods. It is @samp{op$::@var{XXXX}.} where @var{XXXX} is the operator name
-such as @samp{+} or @samp{+=}. The name ends with a period, and any characters except
-the period can occur in the @var{XXXX} string.
-
-The next part of the method description represents the arguments to
-the method, preceeded by a colon and ending with a semi-colon. The
-types of the arguments are expressed in the same way argument types
-are expressed in C++ name mangling. In this example an @code{int} and a @code{char}
+When the field name is a method name it is followed by two colons rather
+than one. This is followed by a new type definition for the method.
+This is a number followed by an equal sign and the type of the method.
+Normally this will be a type declared using the @samp{#} type
+descriptor; see @ref{Method Type Descriptor}; static member functions
+are declared using the @samp{f} type descriptor instead; see
+@ref{Function Types}.
+
+The format of an overloaded operator method name differs from that of
+other methods. It is @samp{op$::@var{operator-name}.} where
+@var{operator-name} is the operator name such as @samp{+} or @samp{+=}.
+The name ends with a period, and any characters except the period can
+occur in the @var{operator-name} string.
+
+The next part of the method description represents the arguments to the
+method, preceded by a colon and ending with a semi-colon. The types of
+the arguments are expressed in the same way argument types are expressed
+in C++ name mangling. In this example an @code{int} and a @code{char}
map to @samp{ic}.
This is followed by a number, a letter, and an asterisk or period,
.stabs "baseA:T20",128,0,0,0
@end smallexample
-@node Class instance
-@section Class instance
+@node Class Instance
+@section Class Instance
As shown above, describing even a simple C++ class definition is
accomplished by massively extending the stab format used in C to
@end example
@node Methods
-@section Method defintion
+@section Method Definition
The class definition shown above declares Ameth. The C++ source below
defines Ameth:
@c GDB. But gpcompare.texi doesn't seem to be in the FSF GCC.
@example
-.stabs "name:symbol_desriptor(global function)return_type(int)",
+.stabs "name:symbol_descriptor(global function)return_type(int)",
N_FUN, NIL, NIL, code_addr_of_method_start
.stabs "Ameth__5baseAic:F1",36,0,0,_Ameth__5baseAic
Here is the stab for the @code{this} pointer implicit argument. The
name of the @code{this} pointer is always @code{this}. Type 19, the
@code{this} pointer is defined as a pointer to type 20, @code{baseA},
-but a stab defining @code{baseA} has not yet been emited. Since the
-compiler knows it will be emited shortly, here it just outputs a cross
+but a stab defining @code{baseA} has not yet been emitted. Since the
+compiler knows it will be emitted shortly, here it just outputs a cross
reference to the undefined symbol, by prefixing the symbol name with
@samp{xs}.
<< The examples that follow are based on A1.C >>
+@node Method Type Descriptor
+@section The @samp{#} Type Descriptor
+
+This is used to describe a class method. This is a function which takes
+an extra argument as its first argument, for the @code{this} pointer.
+
+If the @samp{#} is immediately followed by another @samp{#}, the second
+one will be followed by the return type and a semicolon. The class and
+argument types are not specified, and must be determined by demangling
+the name of the method if it is available.
+
+Otherwise, the single @samp{#} is followed by the class type, a comma,
+the return type, a comma, and zero or more parameter types separated by
+commas. The list of arguments is terminated by a semicolon. In the
+debugging output generated by gcc, a final argument type of @code{void}
+indicates a method which does not take a variable number of arguments.
+If the final argument type of @code{void} does not appear, the method
+was declared with an ellipsis.
+
+Note that although such a type will normally be used to describe fields
+in structures, unions, or classes, for at least some versions of the
+compiler it can also be used in other contexts.
+
+@node Member Type Descriptor
+@section The @samp{@@} Type Descriptor
+
+The @samp{@@} type descriptor is for a member (class and variable) type.
+It is followed by type information for the offset basetype, a comma, and
+type information for the type of the field being pointed to. (FIXME:
+this is acknowledged to be gibberish. Can anyone say what really goes
+here?).
+
+Note that there is a conflict between this and type attributes
+(@pxref{String Field}); both use type descriptor @samp{@@}.
+Fortunately, the @samp{@@} type descriptor used in this C++ sense always
+will be followed by a digit, @samp{(}, or @samp{-}, and type attributes
+never start with those things.
+
@node Protections
@section Protections
-
In the simple class definition shown above all member data and
-functions were publicly accessable. The example that follows
-contrasts public, protected and privately accessable fields and shows
+functions were publicly accessible. The example that follows
+contrasts public, protected and privately accessible fields and shows
how these protections are encoded in C++ stabs.
-Protections for class member data are signified by two characters
-embeded in the stab defining the class type. These characters are
-located after the name: part of the string. @samp{/0} means private, @samp{/1}
-means protected, and @samp{/2} means public. If these characters are omited
-this means that the member is public. The following C++ source:
+If the character following the @samp{@var{field-name}:} part of the
+string is @samp{/}, then the next character is the visibility. @samp{0}
+means private, @samp{1} means protected, and @samp{2} means public.
+Debuggers should ignore visibility characters they do not recognize, and
+assume a reasonable default (such as public) (GDB 4.11 does not, but
+this should be fixed in the next GDB release). If no visibility is
+specified the field is public. The visibility @samp{9} means that the
+field has been optimized out and is public (there is no way to specify
+an optimized out field with a private or protected visibility).
+Visibility @samp{9} is not supported by GDB 4.11; this should be fixed
+in the next GDB release.
+
+The following C++ source:
@example
-class all_data @{
+class vis @{
private:
- int priv_dat;
+ int priv;
protected:
- char prot_dat;
+ char prot;
public:
- float pub_dat;
+ float pub;
@};
@end example
@noindent
-generates the following stab to describe the class type all_data.
+generates the following stab:
-@display
-.stabs "class_name:sym_desc(type)type_def(19)=type_desc(struct)struct_bytes
- data_name:/protection(private)type_ref(int),bit_offset,num_bits;
- data_name:/protection(protected)type_ref(char),bit_offset,num_bits;
- data_name:(/num omited, private)type_ref(float),bit_offset,num_bits;;"
- N_LSYM,NIL,NIL,NIL
-@end display
+@example
+# @r{128 is N_LSYM}
+.stabs "vis:T19=s12priv:/01,0,32;prot:/12,32,8;pub:12,64,32;;",128,0,0,0
+@end example
-@smallexample
-.stabs "all_data:t19=s12
- priv_dat:/01,0,32;prot_dat:/12,32,8;pub_dat:12,64,32;;",128,0,0,0
-@end smallexample
+@samp{vis:T19=s12} indicates that type number 19 is a 12 byte structure
+named @code{vis} The @code{priv} field has public visibility
+(@samp{/0}), type int (@samp{1}), and offset and size @samp{,0,32;}.
+The @code{prot} field has protected visibility (@samp{/1}), type char
+(@samp{2}) and offset and size @samp{,32,8;}. The @code{pub} field has
+type float (@samp{12}), and offset and size @samp{,64,32;}.
-Protections for member functions are signified by one digit embeded in
+Protections for member functions are signified by one digit embedded in
the field part of the stab describing the method. The digit is 0 if
private, 1 if protected and 2 if public. Consider the C++ class
definition below:
meth_name::type_def(22)=sym_desc(method)returning(int);
:args(int);protection(private)modifier(normal)virtual(no);
meth_name::type_def(23)=sym_desc(method)returning(char);
- :args(char);protection(protected)modifier(normal)virual(no);
+ :args(char);protection(protected)modifier(normal)virtual(no);
meth_name::type_def(24)=sym_desc(method)returning(float);
:args(float);protection(public)modifier(normal)virtual(no);;",
N_LSYM,NIL,NIL,NIL
@end smallexample
@node Method Modifiers
-@section Method Modifiers (const, volatile, const volatile)
+@section Method Modifiers (@code{const}, @code{volatile}, @code{const volatile})
<< based on a6.C >>
meth_name(VolatileMeth)::type_def(22)=sym_desc(method)
returning(char);:arg(char);protection(public)modifier(volatile)virt(no)
meth_name(ConstVolMeth)::type_def(23)=sym_desc(method)
- returning(float);:arg(float);protection(public)modifer(const volatile)
+ returning(float);:arg(float);protection(public)modifier(const volatile)
virtual(no);;", @dots{}
@end display
semi-colon.
The second number is a type reference to the first base class in the
-inheritence hierarchy defining the virtual member function. In this
+inheritance hierarchy defining the virtual member function. In this
case the class stab describes a base class so the virtual function is
not overriding any other definition of the method. Therefore the
reference is to the type number of the class that the stab is
For classes containing virtual functions the very last section of the
string part of the stab holds a type reference to the first base
-class. This is preceeded by @samp{~%} and followed by a final semi-colon.
+class. This is preceded by @samp{~%} and followed by a final semi-colon.
@display
.stabs "class_name(A):type_def(20)=sym_desc(struct)struct_bytes(8)
A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0
@end example
-@node Inheritence
-@section Inheritence
+@node Inheritance
+@section Inheritance
Stabs describing C++ derived classes include additional sections that
-describe the inheritence hierarchy of the class. A derived class stab
+describe the inheritance hierarchy of the class. A derived class stab
also encodes the number of base classes. For each base class it tells
-if the base class is virtual or not, and if the inheritence is private
+if the base class is virtual or not, and if the inheritance is private
or public. It also gives the offset into the object of the portion of
the object corresponding to each base class.
-This additional information is embeded in the class stab following the
+This additional information is embedded in the class stab following the
number of bytes in the struct. First the number of base classes
appears bracketed by an exclamation point and a comma.
-Then for each base type there repeats a series: two digits, a number,
-a comma, another number, and a semi-colon.
+Then for each base type there repeats a series: a virtual character, a
+visibility character, a number, a comma, another number, and a
+semi-colon.
-The first of the two digits is 1 if the base class is virtual and 0 if
-not. The second digit is 2 if the derivation is public and 0 if not.
+The virtual character is @samp{1} if the base class is virtual and
+@samp{0} if not. The visibility character is @samp{2} if the derivation
+is public, @samp{1} if it is protected, and @samp{0} if it is private.
+Debuggers should ignore virtual or visibility characters they do not
+recognize, and assume a reasonable default (such as public and
+non-virtual) (GDB 4.11 does not, but this should be fixed in the next
+GDB release).
-The number following the first two digits is the offset from the start
-of the object to the part of the object pertaining to the base class.
+The number following the virtual and visibility characters is the offset
+from the start of the object to the part of the object pertaining to the
+base class.
After the comma, the second number is a type_descriptor for the base
type. Finally a semi-colon ends the series, which repeats for each
@display
.stabs "derived_class_name:symbol_descriptors(struct tag&type)=
type_descriptor(struct)struct_bytes(32)!num_bases(3),
- base_virtual(no)inheritence_public(no)base_offset(0),
+ base_virtual(no)inheritance_public(no)base_offset(0),
base_class_type_ref(A);
- base_virtual(yes)inheritence_public(no)base_offset(NIL),
+ base_virtual(yes)inheritance_public(no)base_offset(NIL),
base_class_type_ref(B);
- base_virtual(no)inheritence_public(yes)base_offset(64),
+ base_virtual(no)inheritance_public(yes)base_offset(64),
base_class_type_ref(C); @dots{}
@end display
@node Virtual Base Classes
@section Virtual Base Classes
-A derived class object consists of a concatination in memory of the
-data areas defined by each base class, starting with the leftmost and
-ending with the rightmost in the list of base classes. The exception
-to this rule is for virtual inheritence. In the example above, class
-@code{D} inherits virtually from base class @code{B}. This means that an instance
-of a @code{D} object will not contain its own @code{B} part but merely a pointer to
-a @code{B} part, known as a virtual base pointer.
+A derived class object consists of a concatenation in memory of the data
+areas defined by each base class, starting with the leftmost and ending
+with the rightmost in the list of base classes. The exception to this
+rule is for virtual inheritance. In the example above, class @code{D}
+inherits virtually from base class @code{B}. This means that an
+instance of a @code{D} object will not contain its own @code{B} part but
+merely a pointer to a @code{B} part, known as a virtual base pointer.
In a derived class stab, the base offset part of the derivation
information, described above, shows how the base class parts are
-ordered. The base offset for a virtual base class is always given as
-0. Notice that the base offset for @code{B} is given as 0 even though @code{B} is
-not the first base class. The first base class @code{A} starts at offset 0.
+ordered. The base offset for a virtual base class is always given as 0.
+Notice that the base offset for @code{B} is given as 0 even though
+@code{B} is not the first base class. The first base class @code{A}
+starts at offset 0.
The field information part of the stab for class @code{D} describes the field
which is the pointer to the virtual base class @code{B}. The vbase pointer
<< How is this reflected in stabs? See Cygnus bug #677 for some info. >>
-@node Example2.c
-@appendix Source code for extended example
-
-@example
-1 char g_foo = 'c';
-2 register int g_bar asm ("%g5");
-3 static int s_g_repeat = 2;
-4 int (*g_pf)();
-5
-6 struct s_tag @{
-7 int s_int;
-8 float s_float;
-9 char s_char_vec[8];
-10 struct s_tag* s_next;
-11 @} g_an_s;
-12
-13 typedef struct s_tag s_typedef;
-14
-15 char char_vec[3] = @{'a','b','c'@};
-16
-17 main (argc, argv)
-18 int argc;
-19 char* argv[];
-20 @{
-21 static float s_flap;
-22 int times;
-23 for (times=0; times < s_g_repeat; times++)@{
-24 int inner;
-25 printf ("Hello world\n");
-26 @}
-27 @};
-28
-29 enum e_places @{first,second=3,last@};
-30
-31 static s_proc (s_arg, s_ptr_arg, char_vec)
-32 s_typedef s_arg;
-33 s_typedef* s_ptr_arg;
-34 char* char_vec;
-35 @{
-36 union u_tag @{
-37 int u_int;
-38 float u_float;
-39 char* u_char;
-40 @} an_u;
-41 @}
-42
-43
-@end example
-
-@node Example2.s
-@appendix Assembly code for extended example
-
-@example
-1 gcc2_compiled.:
-2 .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0
-3 .stabs "example2.c",100,0,0,Ltext0
-4 .text
-5 Ltext0:
-6 .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0
-7 .stabs "char:t2=r2;0;127;",128,0,0,0
-8 .stabs "long int:t3=r1;-2147483648;2147483647;",128,0,0,0
-9 .stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
-10 .stabs "long unsigned int:t5=r1;0;-1;",128,0,0,0
-11 .stabs "short int:t6=r1;-32768;32767;",128,0,0,0
-12 .stabs "long long int:t7=r1;0;-1;",128,0,0,0
-13 .stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0
-14 .stabs "long long unsigned int:t9=r1;0;-1;",128,0,0,0
-15 .stabs "signed char:t10=r1;-128;127;",128,0,0,0
-16 .stabs "unsigned char:t11=r1;0;255;",128,0,0,0
-17 .stabs "float:t12=r1;4;0;",128,0,0,0
-18 .stabs "double:t13=r1;8;0;",128,0,0,0
-19 .stabs "long double:t14=r1;8;0;",128,0,0,0
-20 .stabs "void:t15=15",128,0,0,0
-21 .stabs "g_foo:G2",32,0,0,0
-22 .global _g_foo
-23 .data
-24 _g_foo:
-25 .byte 99
-26 .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat
-27 .align 4
-28 _s_g_repeat:
-29 .word 2
-@c FIXME! fake linebreak in line 30
-30 .stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;s_char_vec:
- 17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0
-31 .stabs "s_typedef:t16",128,0,0,0
-32 .stabs "char_vec:G19=ar1;0;2;2",32,0,0,0
-33 .global _char_vec
-34 .align 4
-35 _char_vec:
-36 .byte 97
-37 .byte 98
-38 .byte 99
-39 .reserve _s_flap.0,4,"bss",4
-40 .text
-41 .align 4
-42 LC0:
-43 .ascii "Hello world\12\0"
-44 .align 4
-45 .global _main
-46 .proc 1
-47 _main:
-48 .stabn 68,0,20,LM1
-49 LM1:
-50 !#PROLOGUE# 0
-51 save %sp,-144,%sp
-52 !#PROLOGUE# 1
-53 st %i0,[%fp+68]
-54 st %i1,[%fp+72]
-55 call ___main,0
-56 nop
-57 LBB2:
-58 .stabn 68,0,23,LM2
-59 LM2:
-60 st %g0,[%fp-20]
-61 L2:
-62 sethi %hi(_s_g_repeat),%o0
-63 ld [%fp-20],%o1
-64 ld [%o0+%lo(_s_g_repeat)],%o0
-65 cmp %o1,%o0
-66 bge L3
-67 nop
-68 LBB3:
-69 .stabn 68,0,25,LM3
-70 LM3:
-71 sethi %hi(LC0),%o1
-72 or %o1,%lo(LC0),%o0
-73 call _printf,0
-74 nop
-75 .stabn 68,0,26,LM4
-76 LM4:
-77 LBE3:
-78 .stabn 68,0,23,LM5
-79 LM5:
-80 L4:
-81 ld [%fp-20],%o0
-82 add %o0,1,%o1
-83 st %o1,[%fp-20]
-84 b,a L2
-85 L3:
-86 .stabn 68,0,27,LM6
-87 LM6:
-88 LBE2:
-89 .stabn 68,0,27,LM7
-90 LM7:
-91 L1:
-92 ret
-93 restore
-94 .stabs "main:F1",36,0,0,_main
-95 .stabs "argc:p1",160,0,0,68
-96 .stabs "argv:p20=*21=*2",160,0,0,72
-97 .stabs "s_flap:V12",40,0,0,_s_flap.0
-98 .stabs "times:1",128,0,0,-20
-99 .stabn 192,0,0,LBB2
-100 .stabs "inner:1",128,0,0,-24
-101 .stabn 192,0,0,LBB3
-102 .stabn 224,0,0,LBE3
-103 .stabn 224,0,0,LBE2
-104 .stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0
-@c FIXME: fake linebreak in line 105
-105 .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
-128,0,0,0
-106 .align 4
-107 .proc 1
-108 _s_proc:
-109 .stabn 68,0,35,LM8
-110 LM8:
-111 !#PROLOGUE# 0
-112 save %sp,-120,%sp
-113 !#PROLOGUE# 1
-114 mov %i0,%o0
-115 st %i1,[%fp+72]
-116 st %i2,[%fp+76]
-117 LBB4:
-118 .stabn 68,0,41,LM9
-119 LM9:
-120 LBE4:
-121 .stabn 68,0,41,LM10
-122 LM10:
-123 L5:
-124 ret
-125 restore
-126 .stabs "s_proc:f1",36,0,0,_s_proc
-127 .stabs "s_arg:p16",160,0,0,0
-128 .stabs "s_ptr_arg:p18",160,0,0,72
-129 .stabs "char_vec:p21",160,0,0,76
-130 .stabs "an_u:23",128,0,0,-20
-131 .stabn 192,0,0,LBB4
-132 .stabn 224,0,0,LBE4
-133 .stabs "g_bar:r1",64,0,0,5
-134 .stabs "g_pf:G24=*25=f1",32,0,0,0
-135 .common _g_pf,4,"bss"
-136 .stabs "g_an_s:G16",32,0,0,0
-137 .common _g_an_s,20,"bss"
-@end example
-
@node Stab Types
-@appendix Table of stab types
+@appendix Table of Stab Types
The following are all the possible values for the stab type field, for
-@code{a.out} files, in numeric order. This does not apply to XCOFF.
+a.out files, in numeric order. This does not apply to XCOFF, but
+it does apply to stabs in sections (@pxref{Stab Sections}). Stabs in
+ECOFF use these values but add 0x8f300 to distinguish them from non-stab
+symbols.
The symbolic names are defined in the file @file{include/aout/stabs.def}.
@menu
-* Non-stab symbol types::
-* Stab symbol types::
+* Non-Stab Symbol Types:: Types from 0 to 0x1f
+* Stab Symbol Types:: Types from 0x20 to 0xff
@end menu
-@node Non-stab symbol types
-@appendixsec Non-stab symbol types
+@node Non-Stab Symbol Types
+@appendixsec Non-Stab Symbol Types
The following types are used by the linker and assembler, not by stab
directives. Since this document does not attempt to describe aspects of
Symbol is indirected to another symbol
@item 0x12 N_COMM
-Common sym -- visable after shared lib dynamic link
+Common---visible after shared library dynamic link
@item 0x14 N_SETA
+@itemx 0x15 N_SETA | N_EXT
Absolute set element
@item 0x16 N_SETT
+@itemx 0x17 N_SETT | N_EXT
Text segment set element
@item 0x18 N_SETD
+@itemx 0x19 N_SETD | N_EXT
Data segment set element
@item 0x1a N_SETB
+@itemx 0x1b N_SETB | N_EXT
BSS segment set element
@item 0x1c N_SETV
+@itemx 0x1d N_SETV | N_EXT
Pointer to set vector
@item 0x1e N_WARNING
File name of a @file{.o} file
@end table
-@node Stab symbol types
-@appendixsec Stab symbol types
+@node Stab Symbol Types
+@appendixsec Stab Symbol Types
The following symbol types indicate that this is a stab. This is the
full list of stab numbers, including stab types that are used in
languages other than C.
-@xref{Expanded reference}, for more information about the stab types.
@table @code
@item 0x20 N_GSYM
-Global symbol; see @ref{N_GSYM}.
+Global symbol; see @ref{Global Variables}.
@item 0x22 N_FNAME
-Function name (for BSD Fortran); see @ref{N_FNAME}.
+Function name (for BSD Fortran); see @ref{Procedures}.
@item 0x24 N_FUN
Function name (@pxref{Procedures}) or text segment variable
@item 0x2a N_MAIN
Name of main routine; see @ref{Main Program}.
-@c FIXME: discuss this in the Statics node where we talk about
-@c the fact that the n_type indicates the section.
@item 0x2c N_ROSYM
Variable in @code{.rodata} section; see @ref{Statics}.
Debugger options (Solaris2).
@item 0x40 N_RSYM
-Register variable; see @ref{N_RSYM}.
+Register variable; see @ref{Register Variables}.
@item 0x42 N_M2C
Modula-2 compilation unit; see @ref{N_M2C}.
Stack variable (@pxref{Stack Variables}) or type (@pxref{Typedefs}).
@item 0x82 N_BINCL
-Beginning of an include file (Sun only); see @ref{Source Files}.
+Beginning of an include file (Sun only); see @ref{Include Files}.
@item 0x84 N_SOL
-Name of include file; see @ref{Source Files}.
+Name of include file; see @ref{Include Files}.
@item 0xa0 N_PSYM
Parameter variable; see @ref{Parameters}.
@item 0xa2 N_EINCL
-End of an include file; see @ref{Source Files}.
+End of an include file; see @ref{Include Files}.
@item 0xa4 N_ENTRY
-Alternate entry point; see @ref{N_ENTRY}.
+Alternate entry point; see @ref{Alternate Entry Points}.
@item 0xc0 N_LBRAC
Beginning of a lexical block; see @ref{Block Structure}.
@item 0xc2 N_EXCL
-Place holder for a deleted include file; see @ref{Source Files}.
+Place holder for a deleted include file; see @ref{Include Files}.
@item 0xc4 N_SCOPE
Modula2 scope information (Sun linker); see @ref{N_SCOPE}.
@node Symbol Descriptors
@appendix Table of Symbol Descriptors
-These tell in the .stabs @var{string} field what kind of symbol the stab
-represents. They follow the symbol name and a colon. @xref{String
-Field}, for more information about their use.
+The symbol descriptor is the character which follows the colon in many
+stabs, and which tells what kind of stab it is. @xref{String Field},
+for more information about their use.
@c Please keep this alphabetical
@table @code
@itemx -
Variable on the stack; see @ref{Stack Variables}.
+@item :
+C++ nested symbol; see @xref{Nested Symbols}.
+
@item a
-Parameter passed by reference in register; see @ref{Parameters}.
+Parameter passed by reference in register; see @ref{Reference Parameters}.
+
+@item b
+Based variable; see @ref{Based Variables}.
@item c
Constant; see @ref{Constants}.
@item C
-Conformant array bound (Pascal, maybe other languages),
-@xref{Parameters}. Name of a caught exception (GNU C++). These can be
-distinguished because the latter uses N_CATCH and the former uses
+Conformant array bound (Pascal, maybe other languages); @ref{Conformant
+Arrays}. Name of a caught exception (GNU C++). These can be
+distinguished because the latter uses @code{N_CATCH} and the former uses
another symbol type.
@item d
-Floating point register variable; see @ref{Register variables}.
+Floating point register variable; see @ref{Register Variables}.
@item D
-Parameter in floating point register; see @ref{Parameters}.
+Parameter in floating point register; see @ref{Register Parameters}.
@item f
File scope function; see @ref{Procedures}.
Global variable; see @ref{Global Variables}.
@item i
-@xref{Parameters}.
+@xref{Register Parameters}.
@item I
-Internal (nested) procedure; see @ref{Procedures}.
+Internal (nested) procedure; see @ref{Nested Procedures}.
@item J
-Internal (nested) function; see @ref{Procedures}.
+Internal (nested) function; see @ref{Nested Procedures}.
@item L
Label name (documented by AIX, no further information known).
Unfortunately, three separate meanings have been independently invented
for this symbol descriptor. At least the GNU and Sun uses can be
distinguished by the symbol type. Global Procedure (AIX) (symbol type
-used unknown); see @ref{Procedures}. Register parameter (GNU) (symbol type
-N_PSYM); see @ref{Parameters}. Prototype of function referenced by this
-file (Sun acc) (symbol type N_FUN).
+used unknown); see @ref{Procedures}. Register parameter (GNU) (symbol
+type @code{N_PSYM}); see @ref{Parameters}. Prototype of function
+referenced by this file (Sun @code{acc}) (symbol type @code{N_FUN}).
@item Q
Static Procedure; see @ref{Procedures}.
@item R
-Register parameter @xref{Parameters}.
+Register parameter; see @ref{Register Parameters}.
@item r
-Register variable; see @ref{Register variables}.
+Register variable; see @ref{Register Variables}.
@item S
File scope variable; see @ref{Statics}.
+@item s
+Local variable (OS9000).
+
@item t
Type name; see @ref{Typedefs}.
@item T
-enumeration, struct or union tag; see @ref{Typedefs}.
+Enumeration, structure, or union tag; see @ref{Typedefs}.
@item v
-Parameter passed by reference; see @ref{Parameters}.
+Parameter passed by reference; see @ref{Reference Parameters}.
@item V
Procedure scope static variable; see @ref{Statics}.
@item x
-Conformant array; see @ref{Parameters}.
+Conformant array; see @ref{Conformant Arrays}.
@item X
Function return variable; see @ref{Parameters}.
@node Type Descriptors
@appendix Table of Type Descriptors
-These tell in the .stabs @var{string} field what kind of type is being
-defined. They follow the type number and an equals sign.
-@xref{Overview}, for more information about their use.
+The type descriptor is the character which follows the type number and
+an equals sign. It specifies what kind of type is being defined.
+@xref{String Field}, for more information about their use.
@table @code
@item @var{digit}
@itemx (
-Type reference; see @ref{Stabs Format}.
+Type reference; see @ref{String Field}.
@item -
Reference to builtin type; see @ref{Negative Type Numbers}.
@item #
-Method (C++); see @ref{Cplusplus}.
+Method (C++); see @ref{Method Type Descriptor}.
@item *
Pointer; see @ref{Miscellaneous Types}.
Reference (C++).
@item @@
-Type Attributes (AIX); see @ref{Stabs Format}. Member (class and variable)
-type (GNU C++); see @ref{Cplusplus}.
+Type Attributes (AIX); see @ref{String Field}. Member (class and variable)
+type (GNU C++); see @ref{Member Type Descriptor}.
@item a
Array; see @ref{Arrays}.
@item b
Pascal space type (AIX); see @ref{Miscellaneous Types}. Builtin integer
-type (Sun); see @ref{Builtin Type Descriptors}.
+type (Sun); see @ref{Builtin Type Descriptors}. Const and volatile
+qualified type (OS9000).
@item B
Volatile-qualified type; see @ref{Miscellaneous Types}.
@item c
-Complex builtin type; see @ref{Builtin Type Descriptors}.
+Complex builtin type (AIX); see @ref{Builtin Type Descriptors}.
+Const-qualified type (OS9000).
@item C
COBOL Picture type. See AIX documentation for details.
COBOL Group. See AIX documentation for details.
@item i
-Imported type; see @ref{Cross-references}.
+Imported type (AIX); see @ref{Cross-References}. Volatile-qualified
+type (OS9000).
@item k
Const-qualified type; see @ref{Miscellaneous Types}.
Wide character; see @ref{Builtin Type Descriptors}.
@item x
-Cross-reference; see @ref{Cross-references}.
+Cross-reference; see @ref{Cross-References}.
+
+@item Y
+Used by IBM's xlC C++ compiler (for structures, I think).
@item z
gstring; see @ref{Strings}.
@end table
-@node Expanded reference
-@appendix Expanded reference by stab type
+@node Expanded Reference
+@appendix Expanded Reference by Stab Type
-@c FIXME: This appendix should go away, see N_PSYM or N_SO for an example.
+@c FIXME: This appendix should go away; see N_PSYM or N_SO for an example.
For a full list of stab types, and cross-references to where they are
-described, see @ref{Stab Types}. This appendix just duplicates certain
-information from the main body of this document; eventually the
-information will all be in one place.
+described, see @ref{Stab Types}. This appendix just covers certain
+stabs which are not yet described in the main body of this document;
+eventually the information will all be in one place.
Format of an entry:
-The first line is the symbol type expressed in decimal, hexadecimal,
-and as a #define (see devo/include/aout/stab.def).
+The first line is the symbol type (see @file{include/aout/stab.def}).
The second line describes the language constructs the symbol type
represents.
named and the rest NIL.
Subsequent lines expand upon the meaning and possible values for each
-significant stab field. # stands in for the type descriptor.
+significant stab field.
Finally, any further information.
@menu
-* N_GSYM:: Global variable
-* N_FNAME:: Function name (BSD Fortran)
* N_PC:: Pascal global symbol
* N_NSYMS:: Number of symbols
* N_NOMAP:: No DST map
-* N_RSYM:: Register variable
* N_M2C:: Modula-2 compilation unit
* N_BROWS:: Path to .cb file for Sun source code browser
* N_DEFD:: GNU Modula2 definition module dependency
* N_MOD2:: Modula2 information "for imc"
* N_CATCH:: GNU C++ "catch" clause
* N_SSYM:: Structure or union element
-* N_ENTRY:: Alternate entry point
* N_SCOPE:: Modula2 scope information (Sun only)
* Gould:: non-base register symbols used on Gould systems
* N_LENG:: Length of preceding entry
@end menu
-@node N_GSYM
-@section 32 - 0x20 - N_GYSM
-
-@display
-Global variable.
-
-.stabs "name", N_GSYM, NIL, NIL, NIL
-@end display
-
-@example
-"name" -> "symbol_name:#type"
- # -> G
-@end example
-
-Only the @var{name} field is significant. The location of the variable is
-obtained from the corresponding external symbol.
-
-@node N_FNAME
-@section 34 - 0x22 - N_FNAME
-Function name (for BSD Fortran)
-
-@display
-.stabs "name", N_FNAME, NIL, NIL, NIL
-@end display
-
-@example
-"name" -> "function_name"
-@end example
-
-Only the "name" field is significant. The location of the symbol is
-obtained from the corresponding extern symbol.
-
@node N_PC
-@section 48 - 0x30 - N_PC
-Global symbol (for Pascal)
+@section N_PC
-@display
-.stabs "name", N_PC, NIL, NIL, value
-@end display
+@deffn @code{.stabs} N_PC
+@findex N_PC
+Global symbol (for Pascal).
@example
"name" -> "symbol_name" <<?>>
@end example
@display
-stabdump.c says:
+@file{stabdump.c} says:
global pascal symbol: name,,0,subtype,line
<< subtype? >>
@end display
+@end deffn
@node N_NSYMS
-@section 50 - 0x32 - N_NSYMS
-Number of symbols (according to Ultrix V4.0)
+@section N_NSYMS
+
+@deffn @code{.stabn} N_NSYMS
+@findex N_NSYMS
+Number of symbols (according to Ultrix V4.0).
@display
0, files,,funcs,lines (stab.def)
@end display
+@end deffn
@node N_NOMAP
-@section 52 - 0x34 - N_NOMAP
+@section N_NOMAP
+
+@deffn @code{.stabs} N_NOMAP
+@findex N_NOMAP
No DST map for symbol (according to Ultrix V4.0). I think this means a
variable has been optimized out.
@display
name, ,0,type,ignored (stab.def)
@end display
-
-@node N_RSYM
-@section 64 - 0x40 - N_RSYM
- register variable
-
-@display
-.stabs "name:type",N_RSYM,0,RegSize,RegNumber (Sun doc)
-@end display
+@end deffn
@node N_M2C
-@section 66 - 0x42 - N_M2C
-Modula-2 compilation unit
+@section N_M2C
-@display
-.stabs "name", N_M2C, 0, desc, value
-@end display
+@deffn @code{.stabs} N_M2C
+@findex N_M2C
+Modula-2 compilation unit.
@example
-"name" -> "unit_name,unit_time_stamp[,code_time_stamp]
+"string" -> "unit_name,unit_time_stamp[,code_time_stamp]"
desc -> unit_number
value -> 0 (main unit)
1 (any other unit)
@end example
+See @cite{Dbx and Dbxtool Interfaces}, 2nd edition, by Sun, 1988, for
+more information.
+
+@end deffn
+
@node N_BROWS
-@section 72 - 0x48 - N_BROWS
+@section N_BROWS
+
+@deffn @code{.stabs} N_BROWS
+@findex N_BROWS
Sun source code browser, path to @file{.cb} file
<<?>>
-"path to associated .cb file"
+"path to associated @file{.cb} file"
-Note: type field value overlaps with N_BSLINE
+Note: N_BROWS has the same value as N_BSLINE.
+@end deffn
@node N_DEFD
-@section 74 - 0x4a - N_DEFD
-GNU Modula2 definition module dependency
+@section N_DEFD
+
+@deffn @code{.stabn} N_DEFD
+@findex N_DEFD
+GNU Modula2 definition module dependency.
-GNU Modula-2 definition module dependency. Value is the modification
-time of the definition file. Other is non-zero if it is imported with
-the GNU M2 keyword %INITIALIZE. Perhaps N_M2C can be used if there
-are enough empty fields?
+GNU Modula-2 definition module dependency. The value is the
+modification time of the definition file. The other field is non-zero
+if it is imported with the GNU M2 keyword @code{%INITIALIZE}. Perhaps
+@code{N_M2C} can be used if there are enough empty fields?
+@end deffn
@node N_EHDECL
-@section 80 - 0x50 - N_EHDECL
-GNU C++ exception variable <<?>>
+@section N_EHDECL
-"name is variable name"
+@deffn @code{.stabs} N_EHDECL
+@findex N_EHDECL
+GNU C++ exception variable <<?>>.
-Note: conflicts with N_MOD2.
+"@var{string} is variable name"
+
+Note: conflicts with @code{N_MOD2}.
+@end deffn
@node N_MOD2
-@section 80 - 0x50 - N_MOD2
+@section N_MOD2
+
+@deffn @code{.stab?} N_MOD2
+@findex N_MOD2
Modula2 info "for imc" (according to Ultrix V4.0)
-Note: conflicts with N_EHDECL <<?>>
+Note: conflicts with @code{N_EHDECL} <<?>>
+@end deffn
@node N_CATCH
-@section 84 - 0x54 - N_CATCH
+@section N_CATCH
+
+@deffn @code{.stabn} N_CATCH
+@findex N_CATCH
GNU C++ @code{catch} clause
-GNU C++ @code{catch} clause. Value is its address. Desc is nonzero if
-this entry is immediately followed by a CAUGHT stab saying what
-exception was caught. Multiple CAUGHT stabs means that multiple
-exceptions can be caught here. If Desc is 0, it means all exceptions
-are caught here.
+GNU C++ @code{catch} clause. The value is its address. The desc field
+is nonzero if this entry is immediately followed by a @code{CAUGHT} stab
+saying what exception was caught. Multiple @code{CAUGHT} stabs means
+that multiple exceptions can be caught here. If desc is 0, it means all
+exceptions are caught here.
+@end deffn
@node N_SSYM
-@section 96 - 0x60 - N_SSYM
-Structure or union element
+@section N_SSYM
-Value is offset in the structure.
+@deffn @code{.stabn} N_SSYM
+@findex N_SSYM
+Structure or union element.
-<<?looking at structs and unions in C I didn't see these>>
-
-@node N_ENTRY
-@section 164 - 0xa4 - N_ENTRY
+The value is the offset in the structure.
-Alternate entry point.
-Value is its address.
-<<?>>
+<<?looking at structs and unions in C I didn't see these>>
+@end deffn
@node N_SCOPE
-@section 196 - 0xc4 - N_SCOPE
+@section N_SCOPE
+@deffn @code{.stab?} N_SCOPE
+@findex N_SCOPE
Modula2 scope information (Sun linker)
<<?>>
+@end deffn
@node Gould
@section Non-base registers on Gould systems
+@deffn @code{.stab?} N_NBTEXT
+@deffnx @code{.stab?} N_NBDATA
+@deffnx @code{.stab?} N_NBBSS
+@deffnx @code{.stab?} N_NBSTS
+@deffnx @code{.stab?} N_NBLCS
+@findex N_NBTEXT
+@findex N_NBDATA
+@findex N_NBBSS
+@findex N_NBSTS
+@findex N_NBLCS
These are used on Gould systems for non-base registers syms.
However, the following values are not the values used by Gould; they are
246 0xf6 N_NBSTS ??
248 0xf8 N_NBLCS ??
@end example
+@end deffn
@node N_LENG
-@section - 0xfe - N_LENG
+@section N_LENG
+@deffn @code{.stabn} N_LENG
+@findex N_LENG
Second symbol entry containing a length-value for the preceding entry.
The value is the length.
+@end deffn
@node Questions
-@appendix Questions and anomalies
+@appendix Questions and Anomalies
@itemize @bullet
@item
+@c I think this is changed in GCC 2.4.5 to put the line number there.
For GNU C stabs defining local and global variables (@code{N_LSYM} and
-@code{N_GSYM}), the @var{desc} field is supposed to contain the source line number
-on which the variable is defined. In reality the @var{desc} field is always
-0. (This behavior is defined in @file{dbxout.c} and putting a line number in
-@var{desc} is controlled by @samp{#ifdef WINNING_GDB}, which defaults to false). GDB
-supposedly uses this information if you say @samp{list @var{var}}. In reality,
-@var{var} can be a variable defined in the program and GDB says @samp{function
+@code{N_GSYM}), the desc field is supposed to contain the source
+line number on which the variable is defined. In reality the desc
+field is always 0. (This behavior is defined in @file{dbxout.c} and
+putting a line number in desc is controlled by @samp{#ifdef
+WINNING_GDB}, which defaults to false). GDB supposedly uses this
+information if you say @samp{list @var{var}}. In reality, @var{var} can
+be a variable defined in the program and GDB says @samp{function
@var{var} not defined}.
@item
structures, unions, and enums (symbol descriptor @samp{T}) and typedefs
(symbol descriptor @samp{t}) defined at file scope from types defined locally
to a procedure or other more local scope. They all use the @code{N_LSYM}
-stab type. Types defined at procedure scope are emited after the
+stab type. Types defined at procedure scope are emitted after the
@code{N_RBRAC} of the preceding function and before the code of the
procedure in which they are defined. This is exactly the same as
types defined in the source file between the two procedure bodies.
-GDB overcompensates by placing all types in block #1, the block for
+GDB over-compensates by placing all types in block #1, the block for
symbols of file scope. This is true for default, @samp{-ansi} and
@samp{-traditional} compiler options. (Bugs gcc/1063, gdb/1066.)
@item
What ends the procedure scope? Is it the proc block's @code{N_RBRAC} or the
next @code{N_FUN}? (I believe its the first.)
-
-@item
-@c FIXME: This should go with the other stuff about global variables.
-Global variable stabs don't have location information. This comes
-from the external symbol for the same variable. The external symbol
-has a leading underbar on the _name of the variable and the stab does
-not. How do we know these two symbol table entries are talking about
-the same symbol when their names are different? (Answer: the debugger
-knows that external symbols have leading underbars).
-
-@c FIXME: This is absurdly vague; there all kinds of differences, some
-@c of which are the same between gnu & sun, and some of which aren't.
-@item
-Can GCC be configured to output stabs the way the Sun compiler
-does, so that their native debugging tools work? <NO?> It doesn't by
-default. GDB reads either format of stab. (GCC or SunC). How about
-DBX?
@end itemize
-@node xcoff-differences
-@appendix Differences between GNU stabs in a.out and GNU stabs in xcoff
-
-@c FIXME: Merge *all* these into the main body of the document.
-The AIX/RS6000 native object file format is xcoff with stabs. This
-appendix only covers those differences which are not covered in the main
-body of this document.
-
-@itemize @bullet
-@item
-BSD a.out stab types correspond to AIX xcoff storage classes. In general the
-mapping is @code{N_STABTYPE} becomes @code{C_STABTYPE}. Some stab types in a.out
-are not supported in xcoff.
-
-@c FIXME: Get C_* types for the block, figure out whether it is always
-@c used (I suspect not), explain clearly, and move to node Statics.
-Exception:
-initialised static @code{N_STSYM} and un-initialized static @code{N_LCSYM} both map
-to the @code{C_STSYM} storage class. But the destinction is preserved
-because in xcoff @code{N_STSYM} and @code{N_LCSYM} must be emited in a named static
-block. Begin the block with @samp{.bs s[RW] data_section_name} for @code{N_STSYM}
-or @samp{.bs s bss_section_name} for @code{N_LCSYM}. End the block with @samp{.es}.
-
-@c FIXME: I think they are trying to say something about whether the
-@c assembler defaults the value to the location counter.
-@item
-If the xcoff stab is a @code{N_FUN} (@code{C_FUN}) then follow the string field with
-@samp{,.} instead of just @samp{,}.
-@end itemize
+@node Stab Sections
+@appendix Using Stabs in Their Own Sections
-I think that's it for @file{.s} file differences. They could stand to be
-better presented. This is just a list of what I have noticed so far.
-There are a @emph{lot} of differences in the information in the symbol
-tables of the executable and object files.
-
-Mapping of a.out stab types to xcoff storage classes:
-
-@example
-stab type storage class
--------------------------------
-N_GSYM C_GSYM
-N_FNAME unknown
-N_FUN C_FUN
-N_STSYM C_STSYM
-N_LCSYM C_STSYM
-N_MAIN unkown
-N_PC unknown
-N_RSYM C_RSYM
-N_RPSYM (0x8e) C_RPSYM
-N_M2C unknown
-N_SLINE unknown
-N_DSLINE unknown
-N_BSLINE unknown
-N_BROWSE unchanged
-N_CATCH unknown
-N_SSYM unknown
-N_SO unknown
-N_LSYM C_LSYM
-N_DECL (0x8c) C_DECL
-N_BINCL unknown
-N_SOL unknown
-N_PSYM C_PSYM
-N_EINCL unknown
-N_ENTRY C_ENTRY
-N_LBRAC unknown
-N_EXCL unknown
-N_SCOPE unknown
-N_RBRAC unknown
-N_BCOMM C_BCOMM
-N_ECOMM C_ECOMM
-N_ECOML C_ECOML
-
-N_LENG unknown
-@end example
-
-@node Sun-differences
-@appendix Differences between GNU stabs and Sun native stabs
-
-@c FIXME: Merge all this stuff into the main body of the document.
+Many object file formats allow tools to create object files with custom
+sections containing any arbitrary data. For any such object file
+format, stabs can be embedded in special sections. This is how stabs
+are used with ELF and SOM, and aside from ECOFF and XCOFF, is how stabs
+are used with COFF.
-@itemize @bullet
-@item
-GNU C stabs define @emph{all} types, file or procedure scope, as
-@code{N_LSYM}. Sun doc talks about using @code{N_GSYM} too.
-
-@item
-Sun C stabs use type number pairs in the format (@var{a},@var{b}) where
-@var{a} is a number starting with 1 and incremented for each sub-source
-file in the compilation. @var{b} is a number starting with 1 and
-incremented for each new type defined in the compilation. GNU C stabs
-use the type number alone, with no source file number.
-@end itemize
+@menu
+* Stab Section Basics:: How to embed stabs in sections
+* ELF Linker Relocation:: Sun ELF hacks
+@end menu
-@node Stabs-in-ELF
-@appendix Using stabs with the ELF object file format
-
-The ELF object file format allows tools to create object files with
-custom sections containing any arbitrary data. To use stabs in ELF
-object files, the tools create two custom sections, a section named
-@code{.stab} which contains an array of fixed length structures, one
-struct per stab, and a section named @code{.stabstr} containing all the
-variable length strings that are referenced by stabs in the @code{.stab}
-section. The byte order of the stabs binary data matches the byte order
-of the ELF file itself, as determined from the @code{EI_DATA} field in
-the @code{e_ident} member of the ELF header.
-
-@c Is "source file" the right term for this concept? We don't mean that
-@c there is a separate one for include files (but "object file" or
-@c "object module" isn't quite right either; the output from ld -r is a
-@c single object file but contains many source files).
-The first stab in the @code{.stab} section for each source file is
+@node Stab Section Basics
+@appendixsec How to Embed Stabs in Sections
+
+The assembler creates two custom sections, a section named @code{.stab}
+which contains an array of fixed length structures, one struct per stab,
+and a section named @code{.stabstr} containing all the variable length
+strings that are referenced by stabs in the @code{.stab} section. The
+byte order of the stabs binary data depends on the object file format.
+For ELF, it matches the byte order of the ELF file itself, as determined
+from the @code{EI_DATA} field in the @code{e_ident} member of the ELF
+header. For SOM, it is always big-endian (is this true??? FIXME). For
+COFF, it matches the byte order of the COFF headers. The meaning of the
+fields is the same as for a.out (@pxref{Symbol Table Format}), except
+that the @code{n_strx} field is relative to the strings for the current
+compilation unit (which can be found using the synthetic N_UNDF stab
+described below), rather than the entire string table.
+
+The first stab in the @code{.stab} section for each compilation unit is
synthetic, generated entirely by the assembler, with no corresponding
@code{.stab} directive as input to the assembler. This stab contains
the following fields:
@item n_other
Unused field, always zero.
+This may eventually be used to hold overflows from the count in
+the @code{n_desc} field.
@item n_desc
Count of upcoming symbols, i.e., the number of remaining stabs for this
@code{sh_link} member set to the section number of the @code{.stabstr}
section, and the @code{.stabstr} section has its ELF section
header @code{sh_type} member set to @code{SHT_STRTAB} to mark it as a
-string table.
-
-Because the linker does not process the @code{.stab} section in any
-special way, none of the addresses in the @code{n_value} field of the
-stabs are relocated by the linker. Instead they are relative to the
-source file (or some entity smaller than a source file, like a
-function). To find the address of each section corresponding to a given
-source file, the (compiler? assembler?) puts out symbols giving the
-address of each section for a given source file. Since these are normal
-ELF symbols, the linker can relocate them correctly. They are
-named @code{Bbss.bss} for the bss section, @code{Ddata.data} for
-the data section, and @code{Drodata.rodata} for the rodata section. I
-haven't yet figured out how the debugger gets the address for the text
-section.
-
+string table. SOM and COFF have no way of linking the sections together
+or marking them as string tables.
+
+For COFF, the @code{.stab} and @code{.stabstr} sections may be simply
+concatenated by the linker. GDB then uses the @code{n_desc} fields to
+figure out the extent of the original sections. Similarly, the
+@code{n_value} fields of the header symbols are added together in order
+to get the actual position of the strings in a desired @code{.stabstr}
+section. Although this design obviates any need for the linker to
+relocate or otherwise manipulate @code{.stab} and @code{.stabstr}
+sections, it also requires some care to ensure that the offsets are
+calculated correctly. For instance, if the linker were to pad in
+between the @code{.stabstr} sections before concatenating, then the
+offsets to strings in the middle of the executable's @code{.stabstr}
+section would be wrong.
+
+The GNU linker is able to optimize stabs information by merging
+duplicate strings and removing duplicate header file information
+(@pxref{Include Files}). When some versions of the GNU linker optimize
+stabs in sections, they remove the leading @code{N_UNDF} symbol and
+arranges for all the @code{n_strx} fields to be relative to the start of
+the @code{.stabstr} section.
+
+@node ELF Linker Relocation
+@appendixsec Having the Linker Relocate Stabs in ELF
+
+This section describes some Sun hacks for Stabs in ELF; it does not
+apply to COFF or SOM.
+
+To keep linking fast, you don't want the linker to have to relocate very
+many stabs. Making sure this is done for @code{N_SLINE},
+@code{N_RBRAC}, and @code{N_LBRAC} stabs is the most important thing
+(see the descriptions of those stabs for more information). But Sun's
+stabs in ELF has taken this further, to make all addresses in the
+@code{n_value} field (functions and static variables) relative to the
+source file. For the @code{N_SO} symbol itself, Sun simply omits the
+address. To find the address of each section corresponding to a given
+source file, the compiler puts out symbols giving the address of each
+section for a given source file. Since these are ELF (not stab)
+symbols, the linker relocates them correctly without having to touch the
+stabs section. They are named @code{Bbss.bss} for the bss section,
+@code{Ddata.data} for the data section, and @code{Drodata.rodata} for
+the rodata section. For the text section, there is no such symbol (but
+there should be, see below). For an example of how these symbols work,
+@xref{Stab Section Transformations}. GCC does not provide these symbols;
+it instead relies on the stabs getting relocated. Thus addresses which
+would normally be relative to @code{Bbss.bss}, etc., are already
+relocated. The Sun linker provided with Solaris 2.2 and earlier
+relocates stabs using normal ELF relocation information, as it would do
+for any section. Sun has been threatening to kludge their linker to not
+do this (to speed up linking), even though the correct way to avoid
+having the linker do these relocations is to have the compiler no longer
+output relocatable values. Last I heard they had been talked out of the
+linker kludge. See Sun point patch 101052-01 and Sun bug 1142109. With
+the Sun compiler this affects @samp{S} symbol descriptor stabs
+(@pxref{Statics}) and functions (@pxref{Procedures}). In the latter
+case, to adopt the clean solution (making the value of the stab relative
+to the start of the compilation unit), it would be necessary to invent a
+@code{Ttext.text} symbol, analogous to the @code{Bbss.bss}, etc.,
+symbols. I recommend this rather than using a zero value and getting
+the address from the ELF symbols.
+
+Finding the correct @code{Bbss.bss}, etc., symbol is difficult, because
+the linker simply concatenates the @code{.stab} sections from each
+@file{.o} file without including any information about which part of a
+@code{.stab} section comes from which @file{.o} file. The way GDB does
+this is to look for an ELF @code{STT_FILE} symbol which has the same
+name as the last component of the file name from the @code{N_SO} symbol
+in the stabs (for example, if the file name is @file{../../gdb/main.c},
+it looks for an ELF @code{STT_FILE} symbol named @code{main.c}). This
+loses if different files have the same name (they could be in different
+directories, a library could have been copied from one system to
+another, etc.). It would be much cleaner to have the @code{Bbss.bss}
+symbols in the stabs themselves. Having the linker relocate them there
+is no more work than having the linker relocate ELF symbols, and it
+solves the problem of having to associate the ELF and stab symbols.
+However, no one has yet designed or implemented such a scheme.
+
+@node Symbol Types Index
+@unnumbered Symbol Types Index
+
+@printindex fn
+
+@c TeX can handle the contents at the start but makeinfo 3.12 can not
+@ifinfo
@contents
+@end ifinfo
+@ifhtml
+@contents
+@end ifhtml
+
@bye
projects / deliverable / binutils-gdb.git / blobdiff