2 @setfilename internals.info
4 @top Assembler Internals
8 This chapter describes the internals of the assembler. It is incomplete, but
11 This chapter was last modified on $Date$. It is not updated regularly, and it
15 * GAS versions:: GAS versions
16 * Data types:: Data types
17 * GAS processing:: What GAS does when it runs
18 * Porting GAS:: Porting GAS
19 * Relaxation:: Relaxation
20 * Broken words:: Broken words
21 * Internal functions:: Internal functions
22 * Test suite:: Test suite
28 GAS has acquired layers of code over time. The original GAS only supported the
29 a.out object file format, with three sections. Support for multiple sections
30 has been added in two different ways.
32 The preferred approach is to use the version of GAS created when the symbol
33 @code{BFD_ASSEMBLER} is defined. The other versions of GAS are documented for
34 historical purposes, and to help anybody who has to debug code written for
37 The type @code{segT} is used to represent a section in code which must work
38 with all versions of GAS.
41 * Original GAS:: Original GAS version
42 * MANY_SEGMENTS:: MANY_SEGMENTS gas version
43 * BFD_ASSEMBLER:: BFD_ASSEMBLER gas version
47 @subsection Original GAS
49 The original GAS only supported the a.out object file format with three
50 sections: @samp{.text}, @samp{.data}, and @samp{.bss}. This is the version of
51 GAS that is compiled if neither @code{BFD_ASSEMBLER} nor @code{MANY_SEGMENTS}
52 is defined. This version of GAS is still used for the m68k-aout target, and
55 This version of GAS should not be used for any new development.
57 There is still code that is specific to this version of GAS, notably in
58 @file{write.c}. There is no way for this code to loop through all the
59 sections; it simply looks at global variables like @code{text_frag_root} and
60 @code{data_frag_root}.
62 The type @code{segT} is an enum.
65 @subsection MANY_SEGMENTS gas version
68 The @code{MANY_SEGMENTS} version of gas is only used for COFF. It uses the BFD
69 library, but it writes out all the data itself using @code{bfd_write}. This
70 version of gas supports up to 40 normal sections. The section names are stored
71 in the @code{seg_name} array. Other information is stored in the
72 @code{segment_info} array.
74 The type @code{segT} is an enum. Code that wants to examine all the sections
75 can use a @code{segT} variable as loop index from @code{SEG_E0} up to but not
76 including @code{SEG_UNKNOWN}.
78 Most of the code specific to this version of GAS is in the file
79 @file{config/obj-coff.c}, in the portion of that file that is compiled when
80 @code{BFD_ASSEMBLER} is not defined.
82 This version of GAS is still used for several COFF targets.
85 @subsection BFD_ASSEMBLER gas version
88 The preferred version of GAS is the @code{BFD_ASSEMBLER} version. In this
89 version of GAS, the output file is a normal BFD, and the BFD routines are used
90 to generate the output.
92 @code{BFD_ASSEMBLER} will automatically be used for certain targets, including
93 those that use the ELF, ECOFF, and SOM object file formats, and also all Alpha,
94 MIPS, PowerPC, and SPARC targets. You can force the use of
95 @code{BFD_ASSEMBLER} for other targets with the configure option
96 @samp{--enable-bfd-assembler}; however, it has not been tested for many
97 targets, and can not be assumed to work.
101 @cindex internals, data types
103 This section describes some fundamental GAS data types.
106 * Symbols:: The symbolS structure
107 * Expressions:: The expressionS structure
108 * Fixups:: The fixS structure
109 * Frags:: The fragS structure
114 @cindex internals, symbols
115 @cindex symbols, internal
116 @cindex symbolS structure
118 The definition for @code{struct symbol}, also known as @code{symbolS}, is
119 located in @file{struc-symbol.h}. Symbol structures contain the following
124 This is an @code{expressionS} that describes the value of the symbol. It might
125 refer to one or more other symbols; if so, its true value may not be known
126 until @code{resolve_symbol_value} is called in @code{write_object_file}.
128 The expression is often simply a constant. Before @code{resolve_symbol_value}
129 is called, the value is the offset from the frag (@pxref{Frags}). Afterward,
130 the frag address has been added in.
133 This field is non-zero if the symbol's value has been completely resolved. It
134 is used during the final pass over the symbol table.
137 This field is used to detect loops while resolving the symbol's value.
139 @item sy_used_in_reloc
140 This field is non-zero if the symbol is used by a relocation entry. If a local
141 symbol is used in a relocation entry, it must be possible to redirect those
142 relocations to other symbols, or this symbol cannot be removed from the final
147 These pointers to other @code{symbolS} structures describe a singly or doubly
148 linked list. (If @code{SYMBOLS_NEED_BACKPOINTERS} is not defined, the
149 @code{sy_previous} field will be omitted; @code{SYMBOLS_NEED_BACKPOINTERS} is
150 always defined if @code{BFD_ASSEMBLER}.) These fields should be accessed with
151 the @code{symbol_next} and @code{symbol_previous} macros.
154 This points to the frag (@pxref{Frags}) that this symbol is attached to.
157 Whether the symbol is used as an operand or in an expression. Note: Not all of
158 the backends keep this information accurate; backends which use this bit are
159 responsible for setting it when a symbol is used in backend routines.
162 Whether the symbol is an MRI common symbol created by the @code{COMMON}
163 pseudo-op when assembling in MRI mode.
166 If @code{BFD_ASSEMBLER} is defined, this points to the BFD @code{asymbol} that
167 will be used in writing the object file.
170 (Only used if @code{BFD_ASSEMBLER} is not defined.) This is the position of
171 the symbol's name in the string table of the object file. On some formats,
172 this will start at position 4, with position 0 reserved for unnamed symbols.
173 This field is not used until @code{write_object_file} is called.
176 (Only used if @code{BFD_ASSEMBLER} is not defined.) This is the
177 format-specific symbol structure, as it would be written into the object file.
180 (Only used if @code{BFD_ASSEMBLER} is not defined.) This is a 24-bit symbol
181 number, for use in constructing relocation table entries.
184 This format-specific data is of type @code{OBJ_SYMFIELD_TYPE}. If no macro by
185 that name is defined in @file{obj-format.h}, this field is not defined.
188 This processor-specific data is of type @code{TC_SYMFIELD_TYPE}. If no macro
189 by that name is defined in @file{targ-cpu.h}, this field is not defined.
191 @item TARGET_SYMBOL_FIELDS
192 If this macro is defined, it defines additional fields in the symbol structure.
193 This macro is obsolete, and should be replaced when possible by uses of
194 @code{OBJ_SYMFIELD_TYPE} and @code{TC_SYMFIELD_TYPE}.
197 There are a number of access routines used to extract the fields of a
198 @code{symbolS} structure. When possible, these routines should be used rather
199 than referring to the fields directly. These routines will work for any GAS
205 Set the symbol's value.
209 Get the symbol's value. This will cause @code{resolve_symbol_value} to be
210 called if necessary, so @code{S_GET_VALUE} should only be called when it is
211 safe to resolve symbols (i.e., after the entire input file has been read and
212 all symbols have been defined).
215 @cindex S_SET_SEGMENT
216 Set the section of the symbol.
219 @cindex S_GET_SEGMENT
220 Get the symbol's section.
224 Get the name of the symbol.
228 Set the name of the symbol.
231 @cindex S_IS_EXTERNAL
232 Return non-zero if the symbol is externally visible.
236 A synonym for @code{S_IS_EXTERNAL}. Don't use it.
240 Return non-zero if the symbol is weak.
244 Return non-zero if this is a common symbol. Common symbols are sometimes
245 represented as undefined symbols with a value, in which case this function will
250 Return non-zero if this symbol is defined. This function is not reliable when
251 called on a common symbol.
255 Return non-zero if this is a debugging symbol.
259 Return non-zero if this is a local assembler symbol which should not be
260 included in the final symbol table. Note that this is not the opposite of
261 @code{S_IS_EXTERNAL}. The @samp{-L} assembler option affects the return value
265 @cindex S_SET_EXTERNAL
266 Mark the symbol as externally visible.
268 @item S_CLEAR_EXTERNAL
269 @cindex S_CLEAR_EXTERNAL
270 Mark the symbol as not externally visible.
274 Mark the symbol as weak.
282 Get the @code{type}, @code{desc}, and @code{other} fields of the symbol. These
283 are only defined for object file formats for which they make sense (primarily
292 Set the @code{type}, @code{desc}, and @code{other} fields of the symbol. These
293 are only defined for object file formats for which they make sense (primarily
298 Get the size of a symbol. This is only defined for object file formats for
299 which it makes sense (primarily ELF).
303 Set the size of a symbol. This is only defined for object file formats for
304 which it makes sense (primarily ELF).
308 @subsection Expressions
309 @cindex internals, expressions
310 @cindex expressions, internal
311 @cindex expressionS structure
313 Expressions are stored in an @code{expressionS} structure. The structure is
314 defined in @file{expr.h}.
317 The macro @code{expression} will create an @code{expressionS} structure based
318 on the text found at the global variable @code{input_line_pointer}.
320 @cindex make_expr_symbol
321 @cindex expr_symbol_where
322 A single @code{expressionS} structure can represent a single operation.
323 Complex expressions are formed by creating @dfn{expression symbols} and
324 combining them in @code{expressionS} structures. An expression symbol is
325 created by calling @code{make_expr_symbol}. An expression symbol should
326 naturally never appear in a symbol table, and the implementation of
327 @code{S_IS_LOCAL} (@pxref{Symbols}) reflects that. The function
328 @code{expr_symbol_where} returns non-zero if a symbol is an expression symbol,
329 and also returns the file and line for the expression which caused it to be
332 The @code{expressionS} structure has two symbol fields, a number field, an
333 operator field, and a field indicating whether the number is unsigned.
335 The operator field is of type @code{operatorT}, and describes how to interpret
336 the other fields; see the definition in @file{expr.h} for the possibilities.
338 An @code{operatorT} value of @code{O_big} indicates either a floating point
339 number, stored in the global variable @code{generic_floating_point_number}, or
340 an integer to large to store in an @code{offsetT} type, stored in the global
341 array @code{generic_bignum}. This rather inflexible approach makes it
342 impossible to use floating point numbers or large expressions in complex
347 @cindex internals, fixups
349 @cindex fixS structure
351 A @dfn{fixup} is basically anything which can not be resolved in the first
352 pass. Sometimes a fixup can be resolved by the end of the assembly; if not,
353 the fixup becomes a relocation entry in the object file.
357 A fixup is created by a call to @code{fix_new} or @code{fix_new_exp}. Both
358 take a frag (@pxref{Frags}), a position within the frag, a size, an indication
359 of whether the fixup is PC relative, and a type. In a @code{BFD_ASSEMBLER}
360 GAS, the type is nominally a @code{bfd_reloc_code_real_type}, but several
361 targets use other type codes to represent fixups that can not be described as
364 The @code{fixS} structure has a number of fields, several of which are obsolete
365 or are only used by a particular target. The important fields are:
369 The frag (@pxref{Frags}) this fixup is in.
372 The location within the frag where the fixup occurs.
375 The symbol this fixup is against. Typically, the value of this symbol is added
376 into the object contents. This may be NULL.
379 The value of this symbol is subtracted from the object contents. This is
383 A number which is added into the fixup.
386 Some CPU backends use this field to convey information between
387 @code{md_apply_fix} and @code{tc_gen_reloc}. The machine independent code does
391 The next fixup in the section.
394 The type of the fixup. This field is only defined if @code{BFD_ASSEMBLER}, or
395 if the target defines @code{NEED_FX_R_TYPE}.
398 The size of the fixup. This is mostly used for error checking.
401 Whether the fixup is PC relative.
404 Non-zero if the fixup has been applied, and no relocation entry needs to be
409 The file and line where the fixup was created.
412 This has the type @code{TC_FIX_TYPE}, and is only defined if the target defines
418 @cindex internals, frags
420 @cindex fragS structure.
422 The @code{fragS} structure is defined in @file{as.h}. Each frag represents a
423 portion of the final object file. As GAS reads the source file, it creates
424 frags to hold the data that it reads. At the end of the assembly the frags and
425 fixups are processed to produce the final contents.
429 The address of the frag. This is not set until the assembler rescans the list
430 of all frags after the entire input file is parsed. The function
431 @code{relax_segment} fills in this field.
434 Pointer to the next frag in this (sub)section.
437 Fixed number of characters we know we're going to emit to the output file. May
441 Variable number of characters we may output, after the initial @code{fr_fix}
442 characters. May be zero.
445 The interpretation of this field is controlled by @code{fr_type}. Generally,
446 if @code{fr_var} is non-zero, this is a repeat count: the @code{fr_var}
447 characters are output @code{fr_offset} times.
450 Holds line number info when an assembler listing was requested.
453 Relaxation state. This field indicates the interpretation of @code{fr_offset},
454 @code{fr_symbol} and the variable-length tail of the frag, as well as the
455 treatment it gets in various phases of processing. It does not affect the
456 initial @code{fr_fix} characters; they are always supposed to be output
457 verbatim (fixups aside). See below for specific values this field can have.
460 Relaxation substate. If the macro @code{md_relax_frag} isn't defined, this is
461 assumed to be an index into @code{TC_GENERIC_RELAX_TABLE} for the generic
462 relaxation code to process (@pxref{Relaxation}). If @code{md_relax_frag} is
463 defined, this field is available for any use by the CPU-specific code.
466 This normally indicates the symbol to use when relaxing the frag according to
470 Points to the lowest-addressed byte of the opcode, for use in relaxation.
472 @item fr_pcrel_adjust
474 These fields are only used in the NS32k configuration. But since @code{struct
475 frag} is defined before the CPU-specific header files are included, they must
476 unconditionally be defined.
480 The file and line where this frag was last modified.
483 Declared as a one-character array, this last field grows arbitrarily large to
484 hold the actual contents of the frag.
487 These are the possible relaxation states, provided in the enumeration type
488 @code{relax_stateT}, and the interpretations they represent for the other
494 The start of the following frag should be aligned on some boundary. In this
495 frag, @code{fr_offset} is the logarithm (base 2) of the alignment in bytes.
496 (For example, if alignment on an 8-byte boundary were desired, @code{fr_offset}
497 would have a value of 3.) The variable characters indicate the fill pattern to
498 be used. Target backends can use @code{rs_align_code} to handle certain types
499 of alignment differently.
502 This indicates that ``broken word'' processing should be done (@pxref{Broken
503 words}). If broken word processing is not necessary on the target machine,
504 this enumerator value will not be defined.
507 The variable characters are to be repeated @code{fr_offset} times. If
508 @code{fr_offset} is 0, this frag has a length of @code{fr_fix}. Most frags
511 @item rs_machine_dependent
512 Displacement relaxation is to be done on this frag. The target is indicated by
513 @code{fr_symbol} and @code{fr_offset}, and @code{fr_subtype} indicates the
514 particular machine-specific addressing mode desired. @xref{Relaxation}.
517 The start of the following frag should be pushed back to some specific offset
518 within the section. (Some assemblers use the value as an absolute address; GAS
519 does not handle final absolute addresses, but rather requires that the linker
520 set them.) The offset is given by @code{fr_symbol} and @code{fr_offset}; one
521 character from the variable-length tail is used as the fill character.
524 @cindex frchainS structure
525 A chain of frags is built up for each subsection. The data structure
526 describing a chain is called a @code{frchainS}, and contains the following
531 Points to the first frag in the chain. May be NULL if there are no frags in
534 Points to the last frag in the chain, or NULL if there are none.
536 Next in the list of @code{frchainS} structures.
538 Indicates the section this frag chain belongs to.
540 Subsection (subsegment) number of this frag chain.
541 @item fix_root, fix_tail
542 (Defined only if @code{BFD_ASSEMBLER} is defined). Point to first and last
543 @code{fixS} structures associated with this subsection.
545 Not currently used. Intended to be used for frag allocation for this
546 subsection. This should reduce frag generation caused by switching sections.
548 The current frag for this subsegment.
551 A @code{frchainS} corresponds to a subsection; each section has a list of
552 @code{frchainS} records associated with it. In most cases, only one subsection
553 of each section is used, so the list will only be one element long, but any
554 processing of frag chains should be prepared to deal with multiple chains per
557 After the input files have been completely processed, and no more frags are to
558 be generated, the frag chains are joined into one per section for further
559 processing. After this point, it is safe to operate on one chain per section.
561 The assembler always has a current frag, named @code{frag_now}. More space is
562 allocated for the current frag using the @code{frag_more} function; this
563 returns a pointer to the amount of requested space. Relaxing is done using
564 variant frags allocated by @code{frag_var} or @code{frag_variant}
565 (@pxref{Relaxation}).
568 @section What GAS does when it runs
569 @cindex internals, overview
571 This is a quick look at what an assembler run looks like.
575 The assembler initializes itself by calling various init routines.
578 For each source file, the @code{read_a_source_file} function reads in the file
579 and parses it. The global variable @code{input_line_pointer} points to the
580 current text; it is guaranteed to be correct up to the end of the line, but not
584 For each line, the assembler passes labels to the @code{colon} function, and
585 isolates the first word. If it looks like a pseudo-op, the word is looked up
586 in the pseudo-op hash table @code{po_hash} and dispatched to a pseudo-op
587 routine. Otherwise, the target dependent @code{md_assemble} routine is called
588 to parse the instruction.
591 When pseudo-ops or instructions output data, they add it to a frag, calling
592 @code{frag_more} to get space to store it in.
595 Pseudo-ops and instructions can also output fixups created by @code{fix_new} or
599 For certain targets, instructions can create variant frags which are used to
600 store relaxation information (@pxref{Relaxation}).
603 When the input file is finished, the @code{write_object_file} routine is
604 called. It assigns addresses to all the frags (@code{relax_segment}), resolves
605 all the fixups (@code{fixup_segment}), resolves all the symbol values (using
606 @code{resolve_symbol_value}), and finally writes out the file (in the
607 @code{BFD_ASSEMBLER} case, this is done by simply calling @code{bfd_close}).
614 Each GAS target specifies two main things: the CPU file and the object format
615 file. Two main switches in the @file{configure.in} file handle this. The
616 first switches on CPU type to set the shell variable @code{cpu_type}. The
617 second switches on the entire target to set the shell variable @code{fmt}.
619 The configure script uses the value of @code{cpu_type} to select two files in
620 the @file{config} directory: @file{tc-@var{CPU}.c} and @file{tc-@var{CPU}.h}.
621 The configuration process will create symlinks to these files from
622 @file{targ-cpu.c} and @file{targ-cpu.h} in the build directory.
624 The configure script also uses the value of @code{fmt} to select two files:
625 @file{obj-@var{fmt}.c} and @file{obj-@var{fmt}.h}. The configuration process
626 will create symlinks to these files from @file{obj-format.h} and
629 You can also set the emulation in the configure script by setting the @code{em}
630 variable. Normally the default value of @samp{generic} is fine. The
631 configuration process will create a symlink from @file{targ-env.h} to
632 @file{te-@var{em}.h}.
634 Porting GAS to a new CPU requires writing the @file{tc-@var{CPU}} files.
635 Porting GAS to a new object file format requires writing the
636 @file{obj-@var{fmt}} files. There is sometimes some interaction between these
637 two files, but it is normally minimal.
639 The best approach is, of course, to copy existing files. The documentation
640 below assumes that you are looking at existing files to see usage details.
642 These interfaces have grown over time, and have never been carefully thought
643 out or designed. Nothing about the interfaces described here is cast in stone.
644 It is possible that they will change from one version of the assembler to the
645 next. Also, new macros are added all the time as they are needed.
648 * CPU backend:: Writing a CPU backend
649 * Object format backend:: Writing an object format backend
650 * Emulations:: Writing emulation files
654 @subsection Writing a CPU backend
656 @cindex @file{tc-@var{CPU}}
658 The CPU backend files are the heart of the assembler. They are the only parts
659 of the assembler which actually know anything about the instruction set of the
662 You must define a reasonably small list of macros and functions in the CPU
663 backend files. You may define a large number of additional macros in the CPU
664 backend files, not all of which are documented here. You must, of course,
665 define macros in the @file{.h} file, which is included by every assembler
666 source file. You may define the functions as macros in the @file{.h} file, or
667 as functions in the @file{.c} file.
672 By convention, you should define this macro in the @file{.h} file. For
673 example, @file{tc-m68k.h} defines @code{TC_M68K}. You might have to use this
674 if it is necessary to add CPU specific code to the object format file.
677 This macro is the BFD target name to use when creating the output file. This
678 will normally depend upon the @code{OBJ_@var{FMT}} macro.
681 This macro is the BFD architecture to pass to @code{bfd_set_arch_mach}.
684 This macro is the BFD machine number to pass to @code{bfd_set_arch_mach}. If
685 it is not defined, GAS will use 0.
687 @item TARGET_BYTES_BIG_ENDIAN
688 You should define this macro to be non-zero if the target is big endian, and
689 zero if the target is little endian.
693 @itemx md_longopts_size
694 @itemx md_parse_option
698 @cindex md_longopts_size
699 @cindex md_parse_option
700 @cindex md_show_usage
701 GAS uses these variables and functions during option processing.
702 @code{md_shortopts} is a @code{const char *} which GAS adds to the machine
703 independent string passed to @code{getopt}. @code{md_longopts} is a
704 @code{struct option []} which GAS adds to the machine independent long options
705 passed to @code{getopt}; you may use @code{OPTION_MD_BASE}, defined in
706 @file{as.h}, as the start of a set of long option indices, if necessary.
707 @code{md_longopts_size} is a @code{size_t} holding the size @code{md_longopts}.
708 GAS will call @code{md_parse_option} whenever @code{getopt} returns an
709 unrecognized code, presumably indicating a special code value which appears in
710 @code{md_longopts}. GAS will call @code{md_show_usage} when a usage message is
711 printed; it should print a description of the machine specific options.
715 GAS will call this function at the start of the assembly, after the command
716 line arguments have been parsed and all the machine independent initializations
721 If you define this macro, GAS will call it at the end of each input file.
725 GAS will call this function for each input line which does not contain a
726 pseudo-op. The argument is a null terminated string. The function should
727 assemble the string as an instruction with operands. Normally
728 @code{md_assemble} will do this by calling @code{frag_more} and writing out
729 some bytes (@pxref{Frags}). @code{md_assemble} will call @code{fix_new} to
730 create fixups as needed (@pxref{Fixups}). Targets which need to do special
731 purpose relaxation will call @code{frag_var}.
733 @item md_pseudo_table
734 @cindex md_pseudo_table
735 This is a const array of type @code{pseudo_typeS}. It is a mapping from
736 pseudo-op names to functions. You should use this table to implement
737 pseudo-ops which are specific to the CPU.
739 @item tc_conditional_pseudoop
740 @cindex tc_conditional_pseudoop
741 If this macro is defined, GAS will call it with a @code{pseudo_typeS} argument.
742 It should return non-zero if the pseudo-op is a conditional which controls
743 whether code is assembled, such as @samp{.if}. GAS knows about the normal
744 conditional pseudo-ops,and you should normally not have to define this macro.
747 @cindex comment_chars
748 This is a null terminated @code{const char} array of characters which start a
751 @item tc_comment_chars
752 @cindex tc_comment_chars
753 If this macro is defined, GAS will use it instead of @code{comment_chars}.
755 @item line_comment_chars
756 @cindex line_comment_chars
757 This is a null terminated @code{const char} array of characters which start a
758 comment when they appear at the start of a line.
760 @item line_separator_chars
761 @cindex line_separator_chars
762 This is a null terminated @code{const char} array of characters which separate
763 lines (the semicolon is such a character by default, and need not be listed in
768 This is a null terminated @code{const char} array of characters which may be
769 used as the exponent character in a floating point number. This is normally
774 This is a null terminated @code{const char} array of characters which may be
775 used to indicate a floating point constant. A zero followed by one of these
776 characters is assumed to be followed by a floating point number; thus they
777 operate the way that @code{0x} is used to indicate a hexadecimal constant.
778 Usually this includes @samp{r} and @samp{f}.
782 You may define this macro to the lexical type of the @kbd{@}} character. The
785 Lexical types are a combination of @code{LEX_NAME} and @code{LEX_BEGIN_NAME},
786 both defined in @file{read.h}. @code{LEX_NAME} indicates that the character
787 may appear in a name. @code{LEX_BEGIN_NAME} indicates that the character may
788 appear at the beginning of a nem.
792 You may define this macro to the lexical type of the brace characters @kbd{@{},
793 @kbd{@}}, @kbd{[}, and @kbd{]}. The default value is zero.
797 You may define this macro to the lexical type of the @kbd{%} character. The
798 default value is zero.
802 You may define this macro to the lexical type of the @kbd{?} character. The
803 default value it zero.
807 You may define this macro to the lexical type of the @kbd{$} character. The
808 default value is @code{LEX_NAME | LEX_BEGIN_NAME}.
810 @item SINGLE_QUOTE_STRINGS
811 @cindex SINGLE_QUOTE_STRINGS
812 If you define this macro, GAS will treat single quotes as string delimiters.
813 Normally only double quotes are accepted as string delimiters.
815 @item NO_STRING_ESCAPES
816 @cindex NO_STRING_ESCAPES
817 If you define this macro, GAS will not permit escape sequences in a string.
819 @item ONLY_STANDARD_ESCAPES
820 @cindex ONLY_STANDARD_ESCAPES
821 If you define this macro, GAS will warn about the use of nonstandard escape
822 sequences in a string.
824 @item md_start_line_hook
825 @cindex md_start_line_hook
826 If you define this macro, GAS will call it at the start of each line.
828 @item LABELS_WITHOUT_COLONS
829 @cindex LABELS_WITHOUT_COLONS
830 If you define this macro, GAS will assume that any text at the start of a line
831 is a label, even if it does not have a colon.
834 @cindex TC_START_LABEL
835 You may define this macro to control what GAS considers to be a label. The
836 default definition is to accept any name followed by a colon character.
839 @cindex NO_PSEUDO_DOT
840 If you define this macro, GAS will not require pseudo-ops to start with a
843 @item TC_EQUAL_IN_INSN
844 @cindex TC_EQUAL_IN_INSN
845 If you define this macro, it should return nonzero if the instruction is
846 permitted to contain an @kbd{=} character. GAS will use this to decide if a
847 @kbd{=} is an assignment or an instruction.
850 @cindex TC_EOL_IN_INSN
851 If you define this macro, it should return nonzero if the current input line
852 pointer should be treated as the end of a line.
855 @cindex md_parse_name
856 If this macro is defined, GAS will call it for any symbol found in an
857 expression. You can define this to handle special symbols in a special way.
858 If a symbol always has a certain value, you should normally enter it in the
859 symbol table, perhaps using @code{reg_section}.
863 GAS will call this function for any expression that can not be recognized.
864 When the function is called, @code{input_line_pointer} will point to the start
867 @item tc_unrecognized_line
868 @cindex tc_unrecognized_line
869 If you define this macro, GAS will call it when it finds a line that it can not
874 You may define this macro to handle an alignment directive. GAS will call it
875 when the directive is seen in the input file. For example, the i386 backend
876 uses this to generate efficient nop instructions of varying lengths, depending
877 upon the number of bytes that the alignment will skip.
881 You may define this macro to do special handling for an alignment directive.
882 GAS will call it at the end of the assembly.
884 @item md_flush_pending_output
885 @cindex md_flush_pending_output
886 If you define this macro, GAS will it each time it skips any space because of a
887 space filling or alignment or data allocation pseudo-op.
889 @item TC_PARSE_CONS_EXPRESSION
890 @cindex TC_PARSE_CONS_EXPRESSION
891 You may define this macro to parse an expression used in a data allocation
892 pseudo-op such as @code{.word}. You can use this to recognize relocation
893 directives that may appear in such directives.
895 @item BITFIELD_CONS_EXPRESSION
896 @cindex BITFIELD_CONS_EXPRESSION
897 If you define this macro, GAS will recognize bitfield instructions in data
898 allocation pseudo-ops, as used on the i960.
900 @item REPEAT_CONS_EXPRESSION
901 @cindex REPEAT_CONS_EXPRESSION
902 If you define this macro, GAS will recognize repeat counts in data allocation
903 pseudo-ops, as used on the MIPS.
906 @cindex md_cons_align
907 You may define this macro to do any special alignment before a data allocation
910 @item TC_CONS_FIX_NEW
911 @cindex TC_CONS_FIX_NEW
912 You may define this macro to generate a fixup for a data allocation pseudo-op.
914 @item md_number_to_chars
915 @cindex md_number_to_chars
916 This should just call either @code{number_to_chars_bigendian} or
917 @code{number_to_chars_littleendian}, whichever is appropriate. On targets like
918 the MIPS which support options to change the endianness, which function to call
919 is a runtime decision. On other targets, @code{md_number_to_chars} can be a
923 @cindex md_reloc_size
924 This variable is only used in the original version of gas (not
925 @code{BFD_ASSEMBLER} and not @code{MANY_SEGMENTS}). It holds the size of a
928 @item WORKING_DOT_WORD
929 @itemx md_short_jump_size
930 @itemx md_long_jump_size
931 @itemx md_create_short_jump
932 @itemx md_create_long_jump
933 @cindex WORKING_DOT_WORD
934 @cindex md_short_jump_size
935 @cindex md_long_jump_size
936 @cindex md_create_short_jump
937 @cindex md_create_long_jump
938 If @code{WORKING_DOT_WORD} is defined, GAS will not do broken word processing
939 (@pxref{Broken words}). Otherwise, you should set @code{md_short_jump_size} to
940 the size of a short jump (a jump that is just long enough to jump around a long
941 jmp) and @code{md_long_jump_size} to the size of a long jump (a jump that can
942 go anywhere in the function), You should define @code{md_create_short_jump} to
943 create a short jump around a long jump, and define @code{md_create_long_jump}
944 to create a long jump.
946 @item md_estimate_size_before_relax
947 @cindex md_estimate_size_before_relax
948 This function returns an estimate of the size of a @code{rs_machine_dependent}
949 frag before any relaxing is done. It may also create any necessary
953 @cindex md_relax_frag
954 This macro may be defined to relax a frag. GAS will call this with the frag
955 and the change in size of all previous frags; @code{md_relax_frag} should
956 return the change in size of the frag. @xref{Relaxation}.
958 @item TC_GENERIC_RELAX_TABLE
959 @cindex TC_GENERIC_RELAX_TABLE
960 If you do not define @code{md_relax_frag}, you may define
961 @code{TC_GENERIC_RELAX_TABLE} as a table of @code{relax_typeS} structures. The
962 machine independent code knows how to use such a table to relax PC relative
963 references. See @file{tc-m68k.c} for an example. @xref{Relaxation}.
965 @item md_prepare_relax_scan
966 @cindex md_prepare_relax_scan
967 If defined, it is a C statement that is invoked prior to scanning
970 @item LINKER_RELAXING_SHRINKS_ONLY
971 @cindex LINKER_RELAXING_SHRINKS_ONLY
972 If you define this macro, and the global variable @samp{linkrelax} is set
973 (because of a command line option, or unconditionally in @code{md_begin}), a
974 @samp{.align} directive will cause extra space to be allocated. The linker can
975 then discard this space when relaxing the section.
977 @item md_convert_frag
978 @cindex md_convert_frag
979 GAS will call this for each rs_machine_dependent fragment.
980 The instruction is completed using the data from the relaxation pass.
981 It may also create an necessary relocations.
986 GAS will call this for each fixup. It should store the correct value in the
989 @item TC_HANDLES_FX_DONE
990 @cindex TC_HANDLES_FX_DONE
991 If this macro is defined, it means that @code{md_apply_fix} correctly sets the
992 @code{fx_done} field in the fixup.
996 A @code{BFD_ASSEMBLER} GAS will call this to generate a reloc. GAS will pass
997 the resulting reloc to @code{bfd_install_relocation}. This currently works
998 poorly, as @code{bfd_install_relocation} often does the wrong thing, and
999 instances of @code{tc_gen_reloc} have been written to work around the problems,
1000 which in turns makes it difficult to fix @code{bfd_install_relocation}.
1002 @item RELOC_EXPANSION_POSSIBLE
1003 @cindex RELOC_EXPANSION_POSSIBLE
1004 If you define this macro, it means that @code{tc_gen_reloc} may return multiple
1005 relocation entries for a single fixup. In this case, the return value of
1006 @code{tc_gen_reloc} is a pointer to a null terminated array.
1008 @item MAX_RELOC_EXPANSION
1009 @cindex MAX_RELOC_EXPANSION
1010 You must define this if @code{RELOC_EXPANSION_POSSIBLE} is defined; it
1011 indicates the largest number of relocs which @code{tc_gen_reloc} may return for
1014 @item tc_fix_adjustable
1015 @cindex tc_fix_adjustable
1016 You may define this macro to indicate whether a fixup against a locally defined
1017 symbol should be adjusted to be against the section symbol. It should return a
1018 non-zero value if the adjustment is acceptable.
1020 @item MD_PCREL_FROM_SECTION
1021 @cindex MD_PCREL_FROM_SECTION
1022 If you define this macro, it should return the offset between the address of a
1023 PC relative fixup and the position from which the PC relative adjustment should
1024 be made. On many processors, the base of a PC relative instruction is the next
1025 instruction, so this macro would return the length of an instruction.
1028 @cindex md_pcrel_from
1029 This is the default value of @code{MD_PCREL_FROM_SECTION}. The difference is
1030 that @code{md_pcrel_from} does not take a section argument.
1033 @cindex tc_frob_label
1034 If you define this macro, GAS will call it each time a label is defined.
1036 @item md_section_align
1037 @cindex md_section_align
1038 GAS will call this function for each section at the end of the assemebly, to
1039 permit the CPU backend to adjust the alignment of a section.
1041 @item tc_frob_section
1042 @cindex tc_frob_section
1043 If you define this macro, a @code{BFD_ASSEMBLER} GAS will call it for each
1044 section at the end of the assembly.
1046 @item tc_frob_file_before_adjust
1047 @cindex tc_frob_file_before_adjust
1048 If you define this macro, GAS will call it after the symbol values are
1049 resolved, but before the fixups have been changed from local symbols to section
1052 @item tc_frob_symbol
1053 @cindex tc_frob_symbol
1054 If you define this macro, GAS will call it for each symbol. You can indicate
1055 that the symbol should not be included in the object file by definining this
1056 macro to set its second argument to a non-zero value.
1059 @cindex tc_frob_file
1060 If you define this macro, GAS will call it after the symbol table has been
1061 completed, but before the relocations have been generated.
1063 @item tc_frob_file_after_relocs
1064 If you define this macro, GAS will call it after the relocs have been
1068 @node Object format backend
1069 @subsection Writing an object format backend
1070 @cindex object format backend
1071 @cindex @file{obj-@var{fmt}}
1073 As with the CPU backend, the object format backend must define a few things,
1074 and may define some other things. The interface to the object format backend
1075 is generally simpler; most of the support for an object file format consists of
1076 defining a number of pseudo-ops.
1078 The object format @file{.h} file must include @file{targ-cpu.h}.
1080 This section will only define the @code{BFD_ASSEMBLER} version of GAS. It is
1081 impossible to support a new object file format using any other version anyhow,
1082 as the original GAS version only supports a.out, and the @code{MANY_SEGMENTS}
1083 GAS version only supports COFF.
1086 @item OBJ_@var{format}
1087 @cindex OBJ_@var{format}
1088 By convention, you should define this macro in the @file{.h} file. For
1089 example, @file{obj-elf.h} defines @code{OBJ_ELF}. You might have to use this
1090 if it is necessary to add object file format specific code to the CPU file.
1093 If you define this macro, GAS will call it at the start of the assembly, after
1094 the command line arguments have been parsed and all the machine independent
1095 initializations have been completed.
1098 @cindex obj_app_file
1099 If you define this macro, GAS will invoke it when it sees a @code{.file}
1100 pseudo-op or a @samp{#} line as used by the C preprocessor.
1102 @item OBJ_COPY_SYMBOL_ATTRIBUTES
1103 @cindex OBJ_COPY_SYMBOL_ATTRIBUTES
1104 You should define this macro to copy object format specific information from
1105 one symbol to another. GAS will call it when one symbol is equated to
1108 @item obj_fix_adjustable
1109 @cindex obj_fix_adjustable
1110 You may define this macro to indicate whether a fixup against a locally defined
1111 symbol should be adjusted to be against the section symbol. It should return a
1112 non-zero value if the adjustment is acceptable.
1114 @item obj_sec_sym_ok_for_reloc
1115 @cindex obj_sec_sym_ok_for_reloc
1116 You may define this macro to indicate that it is OK to use a section symbol in
1117 a relocateion entry. If it is not, GAS will define a new symbol at the start
1120 @item EMIT_SECTION_SYMBOLS
1121 @cindex EMIT_SECTION_SYMBOLS
1122 You should define this macro with a zero value if you do not want to include
1123 section symbols in the output symbol table. The default value for this macro
1126 @item obj_adjust_symtab
1127 @cindex obj_adjust_symtab
1128 If you define this macro, GAS will invoke it just before setting the symbol
1129 table of the output BFD. For example, the COFF support uses this macro to
1130 generate a @code{.file} symbol if none was generated previously.
1132 @item SEPARATE_STAB_SECTIONS
1133 @cindex SEPARATE_STAB_SECTIONS
1134 You may define this macro to indicate that stabs should be placed in separate
1135 sections, as in ELF.
1137 @item INIT_STAB_SECTION
1138 @cindex INIT_STAB_SECTION
1139 You may define this macro to initialize the stabs section in the output file.
1141 @item OBJ_PROCESS_STAB
1142 @cindex OBJ_PROCESS_STAB
1143 You may define this macro to do specific processing on a stabs entry.
1145 @item obj_frob_section
1146 @cindex obj_frob_section
1147 If you define this macro, GAS will call it for each section at the end of the
1150 @item obj_frob_file_before_adjust
1151 @cindex obj_frob_file_before_adjust
1152 If you define this macro, GAS will call it after the symbol values are
1153 resolved, but before the fixups have been changed from local symbols to section
1156 @item obj_frob_symbol
1157 @cindex obj_frob_symbol
1158 If you define this macro, GAS will call it for each symbol. You can indicate
1159 that the symbol should not be included in the object file by definining this
1160 macro to set its second argument to a non-zero value.
1163 @cindex obj_frob_file
1164 If you define this macro, GAS will call it after the symbol table has been
1165 completed, but before the relocations have been generated.
1167 @item obj_frob_file_after_relocs
1168 If you define this macro, GAS will call it after the relocs have been
1173 @subsection Writing emulation files
1175 Normally you do not have to write an emulation file. You can just use
1176 @file{te-generic.h}.
1178 If you do write your own emulation file, it must include @file{obj-format.h}.
1180 An emulation file will often define @code{TE_@var{EM}}; this may then be used
1181 in other files to change the output.
1187 @dfn{Relaxation} is a generic term used when the size of some instruction or
1188 data depends upon the value of some symbol or other data.
1190 GAS knows to relax a particular type of PC relative relocation using a table.
1191 You can also define arbitrarily complex forms of relaxation yourself.
1194 * Relaxing with a table:: Relaxing with a table
1195 * General relaxing:: General relaxing
1198 @node Relaxing with a table
1199 @subsection Relaxing with a table
1201 If you do not define @code{md_relax_frag}, and you do define
1202 @code{TC_GENERIC_RELAX_TABLE}, GAS will relax @code{rs_machine_dependent} frags
1203 based on the frag subtype and the displacement to some specified target
1204 address. The basic idea is that several machines have different addressing
1205 modes for instructions that can specify different ranges of values, with
1206 successive modes able to access wider ranges, including the entirety of the
1207 previous range. Smaller ranges are assumed to be more desirable (perhaps the
1208 instruction requires one word instead of two or three); if this is not the
1209 case, don't describe the smaller-range, inferior mode.
1211 The @code{fr_subtype} field of a frag is an index into a CPU-specific
1212 relaxation table. That table entry indicates the range of values that can be
1213 stored, the number of bytes that will have to be added to the frag to
1214 accomodate the addressing mode, and the index of the next entry to examine if
1215 the value to be stored is outside the range accessible by the current
1216 addressing mode. The @code{fr_symbol} field of the frag indicates what symbol
1217 is to be accessed; the @code{fr_offset} field is added in.
1219 If the @code{fr_pcrel_adjust} field is set, which currently should only happen
1220 for the NS32k family, the @code{TC_PCREL_ADJUST} macro is called on the frag to
1221 compute an adjustment to be made to the displacement.
1223 The value fitted by the relaxation code is always assumed to be a displacement
1224 from the current frag. (More specifically, from @code{fr_fix} bytes into the
1227 This seems kinda silly. What about fitting small absolute values? I suppose
1228 @code{md_assemble} is supposed to take care of that, but if the operand is a
1229 difference between symbols, it might not be able to, if the difference was not
1233 The end of the relaxation sequence is indicated by a ``next'' value of 0. This
1234 means that the first entry in the table can't be used.
1236 For some configurations, the linker can do relaxing within a section of an
1237 object file. If call instructions of various sizes exist, the linker can
1238 determine which should be used in each instance, when a symbol's value is
1239 resolved. In order for the linker to avoid wasting space and having to insert
1240 no-op instructions, it must be able to expand or shrink the section contents
1241 while still preserving intra-section references and meeting alignment
1244 For the i960 using b.out format, no expansion is done; instead, each
1245 @samp{.align} directive causes extra space to be allocated, enough that when
1246 the linker is relaxing a section and removing unneeded space, it can discard
1247 some or all of this extra padding and cause the following data to be correctly
1250 For the H8/300, I think the linker expands calls that can't reach, and doesn't
1251 worry about alignment issues; the cpu probably never needs any significant
1252 alignment beyond the instruction size.
1254 The relaxation table type contains these fields:
1257 @item long rlx_forward
1258 Forward reach, must be non-negative.
1259 @item long rlx_backward
1260 Backward reach, must be zero or negative.
1262 Length in bytes of this addressing mode.
1264 Index of the next-longer relax state, or zero if there is no next relax state.
1267 The relaxation is done in @code{relax_segment} in @file{write.c}. The
1268 difference in the length fields between the original mode and the one finally
1269 chosen by the relaxing code is taken as the size by which the current frag will
1270 be increased in size. For example, if the initial relaxing mode has a length
1271 of 2 bytes, and because of the size of the displacement, it gets upgraded to a
1272 mode with a size of 6 bytes, it is assumed that the frag will grow by 4 bytes.
1273 (The initial two bytes should have been part of the fixed portion of the frag,
1274 since it is already known that they will be output.) This growth must be
1275 effected by @code{md_convert_frag}; it should increase the @code{fr_fix} field
1276 by the appropriate size, and fill in the appropriate bytes of the frag.
1277 (Enough space for the maximum growth should have been allocated in the call to
1278 frag_var as the second argument.)
1280 If relocation records are needed, they should be emitted by
1281 @code{md_estimate_size_before_relax}. This function should examine the target
1282 symbol of the supplied frag and correct the @code{fr_subtype} of the frag if
1283 needed. When this function is called, if the symbol has not yet been defined,
1284 it will not become defined later; however, its value may still change if the
1285 section it is in gets relaxed.
1287 Usually, if the symbol is in the same section as the frag (given by the
1288 @var{sec} argument), the narrowest likely relaxation mode is stored in
1289 @code{fr_subtype}, and that's that.
1291 If the symbol is undefined, or in a different section (and therefore moveable
1292 to an arbitrarily large distance), the largest available relaxation mode is
1293 specified, @code{fix_new} is called to produce the relocation record,
1294 @code{fr_fix} is increased to include the relocated field (remember, this
1295 storage was allocated when @code{frag_var} was called), and @code{frag_wane} is
1296 called to convert the frag to an @code{rs_fill} frag with no variant part.
1297 Sometimes changing addressing modes may also require rewriting the instruction.
1298 It can be accessed via @code{fr_opcode} or @code{fr_fix}.
1300 Sometimes @code{fr_var} is increased instead, and @code{frag_wane} is not
1301 called. I'm not sure, but I think this is to keep @code{fr_fix} referring to
1302 an earlier byte, and @code{fr_subtype} set to @code{rs_machine_dependent} so
1303 that @code{md_convert_frag} will get called.
1305 @node General relaxing
1306 @subsection General relaxing
1308 If using a simple table is not suitable, you may implement arbitrarily complex
1309 relaxation semantics yourself. For example, the MIPS backend uses this to emit
1310 different instruction sequences depending upon the size of the symbol being
1313 When you assemble an instruction that may need relaxation, you should allocate
1314 a frag using @code{frag_var} or @code{frag_variant} with a type of
1315 @code{rs_machine_dependent}. You should store some sort of information in the
1316 @code{fr_subtype} field so that you can figure out what to do with the frag
1319 When GAS reaches the end of the input file, it will look through the frags and
1320 work out their final sizes.
1322 GAS will first call @code{md_estimate_size_before_relax} on each
1323 @code{rs_machine_dependent} frag. This function must return an estimated size
1326 GAS will then loop over the frags, calling @code{md_relax_frag} on each
1327 @code{rs_machine_dependent} frag. This function should return the change in
1328 size of the frag. GAS will keep looping over the frags until none of the frags
1332 @section Broken words
1333 @cindex internals, broken words
1334 @cindex broken words
1336 Some compilers, including GCC, will sometimes emit switch tables specifying
1337 16-bit @code{.word} displacements to branch targets, and branch instructions
1338 that load entries from that table to compute the target address. If this is
1339 done on a 32-bit machine, there is a chance (at least with really large
1340 functions) that the displacement will not fit in 16 bits. The assembler
1341 handles this using a concept called @dfn{broken words}. This idea is well
1342 named, since there is an implied promise that the 16-bit field will in fact
1343 hold the specified displacement.
1345 If broken word processing is enabled, and a situation like this is encountered,
1346 the assembler will insert a jump instruction into the instruction stream, close
1347 enough to be reached with the 16-bit displacement. This jump instruction will
1348 transfer to the real desired target address. Thus, as long as the @code{.word}
1349 value really is used as a displacement to compute an address to jump to, the
1350 net effect will be correct (minus a very small efficiency cost). If
1351 @code{.word} directives with label differences for values are used for other
1352 purposes, however, things may not work properly. For targets which use broken
1353 words, the @samp{-K} option will warn when a broken word is discovered.
1355 The broken word code is turned off by the @code{WORKING_DOT_WORD} macro. It
1356 isn't needed if @code{.word} emits a value large enough to contain an address
1357 (or, more correctly, any possible difference between two addresses).
1359 @node Internal functions
1360 @section Internal functions
1362 This section describes basic internal functions used by GAS.
1365 * Warning and error messages:: Warning and error messages
1366 * Hash tables:: Hash tables
1369 @node Warning and error messages
1370 @subsection Warning and error messages
1372 @deftypefun @{@} int had_warnings (void)
1373 @deftypefunx @{@} int had_errors (void)
1374 Returns non-zero if any warnings or errors, respectively, have been printed
1375 during this invocation.
1378 @deftypefun @{@} void as_perror (const char *@var{gripe}, const char *@var{filename})
1379 Displays a BFD or system error, then clears the error status.
1382 @deftypefun @{@} void as_tsktsk (const char *@var{format}, ...)
1383 @deftypefunx @{@} void as_warn (const char *@var{format}, ...)
1384 @deftypefunx @{@} void as_bad (const char *@var{format}, ...)
1385 @deftypefunx @{@} void as_fatal (const char *@var{format}, ...)
1386 These functions display messages about something amiss with the input file, or
1387 internal problems in the assembler itself. The current file name and line
1388 number are printed, followed by the supplied message, formatted using
1389 @code{vfprintf}, and a final newline.
1391 An error indicated by @code{as_bad} will result in a non-zero exit status when
1392 the assembler has finished. Calling @code{as_fatal} will result in immediate
1393 termination of the assembler process.
1396 @deftypefun @{@} void as_warn_where (char *@var{file}, unsigned int @var{line}, const char *@var{format}, ...)
1397 @deftypefunx @{@} void as_bad_where (char *@var{file}, unsigned int @var{line}, const char *@var{format}, ...)
1398 These variants permit specification of the file name and line number, and are
1399 used when problems are detected when reprocessing information saved away when
1400 processing some earlier part of the file. For example, fixups are processed
1401 after all input has been read, but messages about fixups should refer to the
1402 original filename and line number that they are applicable to.
1405 @deftypefun @{@} void fprint_value (FILE *@var{file}, valueT @var{val})
1406 @deftypefunx @{@} void sprint_value (char *@var{buf}, valueT @var{val})
1407 These functions are helpful for converting a @code{valueT} value into printable
1408 format, in case it's wider than modes that @code{*printf} can handle. If the
1409 type is narrow enough, a decimal number will be produced; otherwise, it will be
1410 in hexadecimal. The value itself is not examined to make this determination.
1414 @subsection Hash tables
1417 @deftypefun @{@} @{struct hash_control *@} hash_new (void)
1418 Creates the hash table control structure.
1421 @deftypefun @{@} void hash_die (struct hash_control *)
1422 Destroy a hash table.
1425 @deftypefun @{@} PTR hash_delete (struct hash_control *, const char *)
1426 Deletes entry from the hash table, returns the value it had.
1429 @deftypefun @{@} PTR hash_replace (struct hash_control *, const char *, PTR)
1430 Updates the value for an entry already in the table, returning the old value.
1431 If no entry was found, just returns NULL.
1434 @deftypefun @{@} @{const char *@} hash_insert (struct hash_control *, const char *, PTR)
1435 Inserting a value already in the table is an error.
1436 Returns an error message or NULL.
1439 @deftypefun @{@} @{const char *@} hash_jam (struct hash_control *, const char *, PTR)
1440 Inserts if the value isn't already present, updates it if it is.
1447 The test suite is kind of lame for most processors. Often it only checks to
1448 see if a couple of files can be assembled without the assembler reporting any
1449 errors. For more complete testing, write a test which either examines the
1450 assembler listing, or runs @code{objdump} and examines its output. For the
1451 latter, the TCL procedure @code{run_dump_test} may come in handy. It takes the
1452 base name of a file, and looks for @file{@var{file}.d}. This file should
1453 contain as its initial lines a set of variable settings in @samp{#} comments,
1457 #@var{varname}: @var{value}
1460 The @var{varname} may be @code{objdump}, @code{nm}, or @code{as}, in which case
1461 it specifies the options to be passed to the specified programs. Exactly one
1462 of @code{objdump} or @code{nm} must be specified, as that also specifies which
1463 program to run after the assembler has finished. If @var{varname} is
1464 @code{source}, it specifies the name of the source file; otherwise,
1465 @file{@var{file}.s} is used. If @var{varname} is @code{name}, it specifies the
1466 name of the test to be used in the @code{pass} or @code{fail} messages.
1468 The non-commented parts of the file are interpreted as regular expressions, one
1469 per line. Blank lines in the @code{objdump} or @code{nm} output are skipped,
1470 as are blank lines in the @code{.d} file; the other lines are tested to see if
1471 the regular expression matches the program output. If it does not, the test
1474 Note that this means the tests must be modified if the @code{objdump} output