-@c Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008
-@c Free Software Foundation, Inc.
+@c Copyright (C) 2002-2019 Free Software Foundation, Inc.
@c This is part of the GAS manual.
@c For copying conditions, see the file as.texinfo.
@c
@end menu
@node Xtensa Options
-@section Command Line Options
+@section Command-line Options
@c man begin OPTIONS
@table @gcctabopt
literals are interspersed in the text section in order to keep them as
close as possible to their references. This may be necessary for large
assembly files, where the literals would otherwise be out of range of the
-@code{L32R} instructions in the text section. These options only affect
+@code{L32R} instructions in the text section. Literals are grouped into
+pools following @code{.literal_position} directives or preceding
+@code{ENTRY} instructions. These options only affect literals referenced
+via PC-relative @code{L32R} instructions; literals for absolute mode
+@code{L32R} instructions are handled separately.
+@xref{Literal Directive, ,literal}.
+
+@item --auto-litpools | --no-auto-litpools
+@kindex --auto-litpools
+@kindex --no-auto-litpools
+Control the treatment of literal pools. The default is
+@samp{--no-@-auto-@-litpools}, which in the absence of
+@samp{--text-@-section-@-literals} places literals in separate sections
+in the output file. This allows the literal pool to be placed in a data
+RAM/ROM. With @samp{--auto-@-litpools}, the literals are interspersed
+in the text section in order to keep them as close as possible to their
+references, explicit @code{.literal_position} directives are not
+required. This may be necessary for very large functions, where single
+literal pool at the beginning of the function may not be reachable by
+@code{L32R} instructions at the end. These options only affect
literals referenced via PC-relative @code{L32R} instructions; literals
for absolute mode @code{L32R} instructions are handled separately.
+When used together with @samp{--text-@-section-@-literals},
+@samp{--auto-@-litpools} takes precedence.
@xref{Literal Directive, ,literal}.
@item --absolute-literals | --no-absolute-literals
@kindex --rename-section
Rename the @var{oldname} section to @var{newname}. This option can be used
multiple times to rename multiple sections.
+
+@item --trampolines | --no-trampolines
+@kindex --trampolines
+@kindex --no-trampolines
+Enable or disable transformation of jump instructions to allow jumps
+across a greater range of addresses. @xref{Xtensa Jump Relaxation,
+,Jump Trampolines}. This option should be used when jump targets can
+potentially be out of range. In the absence of such jumps this option
+does not affect code size or performance. The default is
+@samp{--trampolines}.
@end table
@c man end
Block comments are delimited by @samp{/*} and @samp{*/}. End of line
comments may be introduced with either @samp{#} or @samp{//}.
+If a @samp{#} appears as the first character of a line then the whole
+line is treated as a comment, but in this case the line could also be
+a logical line number directive (@pxref{Comments}) or a preprocessor
+control command (@pxref{Preprocessing}).
+
Instructions consist of a leading opcode or macro name followed by
whitespace and an optional comma-separated list of operands:
@var{opcode} [@var{operand}, @dots{}]
@end smallexample
-Instructions must be separated by a newline or semicolon.
+Instructions must be separated by a newline or semicolon (@samp{;}).
FLIX instructions, which bundle multiple opcodes together in a single
instruction, are specified by enclosing the bundled opcodes inside
some expense in code size.
This optimization is enabled by default. You can disable it with the
@samp{--no-target-@-align} command-line option (@pxref{Xtensa Options,
-,Command Line Options}).
+,Command-line Options}).
The target alignment optimization is done without adding instructions
that could increase the execution time of the program. If there are
@menu
* Xtensa Branch Relaxation:: Relaxation of Branches.
* Xtensa Call Relaxation:: Relaxation of Function Calls.
+* Xtensa Jump Relaxation:: Relaxation of Jumps.
* Xtensa Immediate Relaxation:: Relaxation of other Immediate Fields.
@end menu
Branch relaxation is enabled by default. It can be disabled by using
underscore prefixes (@pxref{Xtensa Opcodes, ,Opcode Names}), the
@samp{--no-transform} command-line option (@pxref{Xtensa Options,
-,Command Line Options}), or the @code{no-transform} directive
+,Command-line Options}), or the @code{no-transform} directive
(@pxref{Transform Directive, ,transform}).
@node Xtensa Call Relaxation
enabled using the @samp{--longcalls} command-line option or the
@code{longcalls} directive (@pxref{Longcalls Directive, ,longcalls}).
+@node Xtensa Jump Relaxation
+@subsection Jump Relaxation
+@cindex relaxation of jump instructions
+@cindex jump instructions, relaxation
+
+Jump instruction may require relaxation because the Xtensa jump instruction
+(@code{J}) provide a PC-relative offset of only 128 Kbytes in either
+direction. One option is to use jump long (@code{J.L}) instruction, which
+depending on jump distance may be assembled as jump (@code{J}) or indirect
+jump (@code{JX}). However it needs a free register. When there's no spare
+register it is possible to plant intermediate jump sites (trampolines)
+between the jump instruction and its target. These sites may be located in
+areas unreachable by normal code execution flow, in that case they only
+contain intermediate jumps, or they may be inserted in the middle of code
+block, in which case there's an additional jump from the beginning of the
+trampoline to the instruction past its end. So, for example:
+
+@smallexample
+@group
+ j 1f
+ ...
+ retw
+ ...
+ mov a10, a2
+ call8 func
+ ...
+1:
+ ...
+@end group
+@end smallexample
+
+might be relaxed to:
+
+@smallexample
+@group
+ j .L0_TR_1
+ ...
+ retw
+.L0_TR_1:
+ j 1f
+ ...
+ mov a10, a2
+ call8 func
+ ...
+1:
+ ...
+@end group
+@end smallexample
+
+or to:
+
+@smallexample
+@group
+ j .L0_TR_1
+ ...
+ retw
+ ...
+ mov a10, a2
+ j .L0_TR_0
+.L0_TR_1:
+ j 1f
+.L0_TR_0:
+ call8 func
+ ...
+1:
+ ...
+@end group
+@end smallexample
+
+The Xtensa assembler uses trampolines with jump around only when it cannot
+find suitable unreachable trampoline. There may be multiple trampolines
+between the jump instruction and its target.
+
+This relaxation does not apply to jumps to undefined symbols, assuming they
+will reach their targets once resolved.
+
+Jump relaxation is enabled by default because it does not affect code size
+or performance while the code itself is small. This relaxation may be
+disabled completely with @samp{--no-trampolines} or @samp{--no-transform}
+command-line options (@pxref{Xtensa Options, ,Command-line Options}).
+
@node Xtensa Immediate Relaxation
@subsection Other Immediate Field Relaxation
@cindex immediate fields, relaxation
The assembler normally performs the following other relaxations. They
can be disabled by using underscore prefixes (@pxref{Xtensa Opcodes,
,Opcode Names}), the @samp{--no-transform} command-line option
-(@pxref{Xtensa Options, ,Command Line Options}), or the
+(@pxref{Xtensa Options, ,Command-line Options}), or the
@code{no-transform} directive (@pxref{Transform Directive, ,transform}).
@cindex @code{MOVI} instructions, relaxation
@subsection literal
@cindex @code{literal} directive
-The @code{.literal} directive is used to define literal pool data, i.e.,
+The @code{.literal} directive is used to define literal pool data, i.e.,
read-only 32-bit data accessed via @code{L32R} instructions.
@smallexample
Literal pools are placed by default in separate literal sections;
however, when using the @samp{--text-@-section-@-literals}
-option (@pxref{Xtensa Options, ,Command Line Options}), the literal
+option (@pxref{Xtensa Options, ,Command-line Options}), the literal
pools for PC-relative mode @code{L32R} instructions
are placed in the current section.@footnote{Literals for the
@code{.init} and @code{.fini} sections are always placed in separate
@samp{--text-@-section-@-literals} option is not used or when
@code{L32R} instructions use the absolute addressing mode.
-The assembler will automatically place text section literal pools
+The assembler will automatically place text section literal pools
before @code{ENTRY} instructions, so the @code{.literal_position}
directive is only needed to specify some other location for a literal
pool. You may need to add an explicit jump instruction to skip over an
argument is omitted, the literal sections revert to the defaults. This
directive has no effect when using the
@samp{--text-@-section-@-literals} option (@pxref{Xtensa Options,
-,Command Line Options}).
+,Command-line Options}).
@node Absolute Literals Directive
@subsection absolute-literals
projects / deliverable / binutils-gdb.git / blobdiff