1 @c Copyright (C) 2009-2016 Free Software Foundation, Inc.
2 @c Contributed by ARM Ltd.
3 @c This is part of the GAS manual.
4 @c For copying conditions, see the file as.texinfo.
9 @node AArch64-Dependent
10 @chapter AArch64 Dependent Features
14 @node Machine Dependencies
15 @chapter AArch64 Dependent Features
18 @cindex AArch64 support
20 * AArch64 Options:: Options
21 * AArch64 Extensions:: Extensions
22 * AArch64 Syntax:: Syntax
23 * AArch64 Floating Point:: Floating Point
24 * AArch64 Directives:: AArch64 Machine Directives
25 * AArch64 Opcodes:: Opcodes
26 * AArch64 Mapping Symbols:: Mapping Symbols
31 @cindex AArch64 options (none)
32 @cindex options for AArch64 (none)
37 @cindex @option{-EB} command line option, AArch64
39 This option specifies that the output generated by the assembler should
40 be marked as being encoded for a big-endian processor.
42 @cindex @option{-EL} command line option, AArch64
44 This option specifies that the output generated by the assembler should
45 be marked as being encoded for a little-endian processor.
47 @cindex @option{-mabi=} command line option, AArch64
49 Specify which ABI the source code uses. The recognized arguments
50 are: @code{ilp32} and @code{lp64}, which decides the generated object
51 file in ELF32 and ELF64 format respectively. The default is @code{lp64}.
53 @cindex @option{-mcpu=} command line option, AArch64
54 @item -mcpu=@var{processor}[+@var{extension}@dots{}]
55 This option specifies the target processor. The assembler will issue an error
56 message if an attempt is made to assemble an instruction which will not execute
57 on the target processor. The following processor names are recognized:
70 The special name @code{all} may be used to allow the assembler to accept
71 instructions valid for any supported processor, including all optional
74 In addition to the basic instruction set, the assembler can be told to
75 accept, or restrict, various extension mnemonics that extend the
76 processor. @xref{AArch64 Extensions}.
78 If some implementations of a particular processor can have an
79 extension, then then those extensions are automatically enabled.
80 Consequently, you will not normally have to specify any additional
83 @cindex @option{-march=} command line option, AArch64
84 @item -march=@var{architecture}[+@var{extension}@dots{}]
85 This option specifies the target architecture. The assembler will
86 issue an error message if an attempt is made to assemble an
87 instruction which will not execute on the target architecture. The
88 following architecture names are recognized: @code{armv8-a},
89 @code{armv8.1-a} and @code{armv8.2-a}.
91 If both @option{-mcpu} and @option{-march} are specified, the
92 assembler will use the setting for @option{-mcpu}. If neither are
93 specified, the assembler will default to @option{-mcpu=all}.
95 The architecture option can be extended with the same instruction set
96 extension options as the @option{-mcpu} option. Unlike
97 @option{-mcpu}, extensions are not always enabled by default,
98 @xref{AArch64 Extensions}.
100 @cindex @code{-mverbose-error} command line option, AArch64
101 @item -mverbose-error
102 This option enables verbose error messages for AArch64 gas. This option
103 is enabled by default.
105 @cindex @code{-mno-verbose-error} command line option, AArch64
106 @item -mno-verbose-error
107 This option disables verbose error messages in AArch64 gas.
112 @node AArch64 Extensions
113 @section Architecture Extensions
115 The table below lists the permitted architecture extensions that are
116 supported by the assembler and the conditions under which they are
117 automatically enabled.
119 Multiple extensions may be specified, separated by a @code{+}.
120 Extension mnemonics may also be removed from those the assembler
121 accepts. This is done by prepending @code{no} to the option that adds
122 the extension. Extensions that are removed must be listed after all
123 extensions that have been added.
125 Enabling an extension that requires other extensions will
126 automatically cause those extensions to be enabled. Similarly,
127 disabling an extension that is required by other extensions will
128 automatically cause those extensions to be disabled.
130 @multitable @columnfractions .12 .17 .17 .54
131 @headitem Extension @tab Minimum Architecture @tab Enabled by default
133 @item @code{crc} @tab ARMv8-A @tab ARMv8.1-A or later
134 @tab Enable CRC instructions.
135 @item @code{crypto} @tab ARMv8-A @tab No
136 @tab Enable cryptographic extensions. This implies @code{fp} and @code{simd}.
137 @item @code{fp} @tab ARMv8-A @tab ARMv8-A or later
138 @tab Enable floating-point extensions.
139 @item @code{fp16} @tab ARMv8.2-A @tab ARMv8.2-A or later
140 @tab Enable ARMv8.2 16-bit floating-point support. This implies
142 @item @code{lor} @tab ARMv8-A @tab ARMv8.1-A or later
143 @tab Enable Limited Ordering Regions extensions.
144 @item @code{lse} @tab ARMv8-A @tab ARMv8.1-A or later
145 @tab Enable Large System extensions.
146 @item @code{pan} @tab ARMv8-A @tab ARMv8.1-A or later
147 @tab Enable Privileged Access Never support.
148 @item @code{profile} @tab ARMv8.2-A @tab No
149 @tab Enable statistical profiling extensions.
150 @item @code{ras} @tab ARMv8-A @tab ARMv8.2-A or later
151 @tab Enable the Reliability, Availability and Serviceability
153 @item @code{rdma} @tab ARMv8-A @tab ARMv8.1-A or later
154 @tab Enable ARMv8.1 Advanced SIMD extensions. This implies @code{simd}.
155 @item @code{simd} @tab ARMv8-A @tab ARMv8-A or later
156 @tab Enable Advanced SIMD extensions. This implies @code{fp}.
162 * AArch64-Chars:: Special Characters
163 * AArch64-Regs:: Register Names
164 * AArch64-Relocations:: Relocations
168 @subsection Special Characters
170 @cindex line comment character, AArch64
171 @cindex AArch64 line comment character
172 The presence of a @samp{//} on a line indicates the start of a comment
173 that extends to the end of the current line. If a @samp{#} appears as
174 the first character of a line, the whole line is treated as a comment.
176 @cindex line separator, AArch64
177 @cindex statement separator, AArch64
178 @cindex AArch64 line separator
179 The @samp{;} character can be used instead of a newline to separate
182 @cindex immediate character, AArch64
183 @cindex AArch64 immediate character
184 The @samp{#} can be optionally used to indicate immediate operands.
187 @subsection Register Names
189 @cindex AArch64 register names
190 @cindex register names, AArch64
191 Please refer to the section @samp{4.4 Register Names} of
192 @samp{ARMv8 Instruction Set Overview}, which is available at
193 @uref{http://infocenter.arm.com}.
195 @node AArch64-Relocations
196 @subsection Relocations
198 @cindex relocations, AArch64
199 @cindex AArch64 relocations
200 @cindex MOVN, MOVZ and MOVK group relocations, AArch64
201 Relocations for @samp{MOVZ} and @samp{MOVK} instructions can be generated
202 by prefixing the label with @samp{#:abs_g2:} etc.
203 For example to load the 48-bit absolute address of @var{foo} into x0:
206 movz x0, #:abs_g2:foo // bits 32-47, overflow check
207 movk x0, #:abs_g1_nc:foo // bits 16-31, no overflow check
208 movk x0, #:abs_g0_nc:foo // bits 0-15, no overflow check
211 @cindex ADRP, ADD, LDR/STR group relocations, AArch64
212 Relocations for @samp{ADRP}, and @samp{ADD}, @samp{LDR} or @samp{STR}
213 instructions can be generated by prefixing the label with
214 @samp{:pg_hi21:} and @samp{#:lo12:} respectively.
216 For example to use 33-bit (+/-4GB) pc-relative addressing to
217 load the address of @var{foo} into x0:
220 adrp x0, :pg_hi21:foo
221 add x0, x0, #:lo12:foo
224 Or to load the value of @var{foo} into x0:
227 adrp x0, :pg_hi21:foo
228 ldr x0, [x0, #:lo12:foo]
231 Note that @samp{:pg_hi21:} is optional.
240 adrp x0, :pg_hi21:foo
243 @node AArch64 Floating Point
244 @section Floating Point
246 @cindex floating point, AArch64 (@sc{ieee})
247 @cindex AArch64 floating point (@sc{ieee})
248 The AArch64 architecture uses @sc{ieee} floating-point numbers.
250 @node AArch64 Directives
251 @section AArch64 Machine Directives
253 @cindex machine directives, AArch64
254 @cindex AArch64 machine directives
257 @c AAAAAAAAAAAAAAAAAAAAAAAAA
259 @cindex @code{.arch} directive, AArch64
260 @item .arch @var{name}
261 Select the target architecture. Valid values for @var{name} are the same as
262 for the @option{-march} commandline option.
264 Specifying @code{.arch} clears any previously selected architecture
267 @cindex @code{.arch_extension} directive, AArch64
268 @item .arch_extension @var{name}
269 Add or remove an architecture extension to the target architecture. Valid
270 values for @var{name} are the same as those accepted as architectural
271 extensions by the @option{-mcpu} commandline option.
273 @code{.arch_extension} may be used multiple times to add or remove extensions
274 incrementally to the architecture being compiled for.
276 @c BBBBBBBBBBBBBBBBBBBBBBBBBB
278 @cindex @code{.bss} directive, AArch64
280 This directive switches to the @code{.bss} section.
282 @c CCCCCCCCCCCCCCCCCCCCCCCCCC
284 @cindex @code{.cpu} directive, AArch64
285 @item .cpu @var{name}
286 Set the target processor. Valid values for @var{name} are the same as
287 those accepted by the @option{-mcpu=} command line option.
289 @c DDDDDDDDDDDDDDDDDDDDDDDDDD
291 @cindex @code{.dword} directive, AArch64
292 @item .dword @var{expressions}
293 The @code{.dword} directive produces 64 bit values.
295 @c EEEEEEEEEEEEEEEEEEEEEEEEEE
297 @cindex @code{.even} directive, AArch64
299 The @code{.even} directive aligns the output on the next even byte
302 @c FFFFFFFFFFFFFFFFFFFFFFFFFF
303 @c GGGGGGGGGGGGGGGGGGGGGGGGGG
304 @c HHHHHHHHHHHHHHHHHHHHHHHHHH
305 @c IIIIIIIIIIIIIIIIIIIIIIIIII
307 @cindex @code{.inst} directive, AArch64
308 @item .inst @var{expressions}
309 Inserts the expressions into the output as if they were instructions,
312 @c JJJJJJJJJJJJJJJJJJJJJJJJJJ
313 @c KKKKKKKKKKKKKKKKKKKKKKKKKK
314 @c LLLLLLLLLLLLLLLLLLLLLLLLLL
316 @cindex @code{.ltorg} directive, AArch64
318 This directive causes the current contents of the literal pool to be
319 dumped into the current section (which is assumed to be the .text
320 section) at the current location (aligned to a word boundary).
321 GAS maintains a separate literal pool for each section and each
322 sub-section. The @code{.ltorg} directive will only affect the literal
323 pool of the current section and sub-section. At the end of assembly
324 all remaining, un-empty literal pools will automatically be dumped.
326 Note - older versions of GAS would dump the current literal
327 pool any time a section change occurred. This is no longer done, since
328 it prevents accurate control of the placement of literal pools.
330 @c MMMMMMMMMMMMMMMMMMMMMMMMMM
332 @c NNNNNNNNNNNNNNNNNNNNNNNNNN
333 @c OOOOOOOOOOOOOOOOOOOOOOOOOO
335 @c PPPPPPPPPPPPPPPPPPPPPPPPPP
337 @cindex @code{.pool} directive, AArch64
339 This is a synonym for .ltorg.
341 @c QQQQQQQQQQQQQQQQQQQQQQQQQQ
342 @c RRRRRRRRRRRRRRRRRRRRRRRRRR
344 @cindex @code{.req} directive, AArch64
345 @item @var{name} .req @var{register name}
346 This creates an alias for @var{register name} called @var{name}. For
353 @c SSSSSSSSSSSSSSSSSSSSSSSSSS
355 @c TTTTTTTTTTTTTTTTTTTTTTTTTT
357 @cindex @code{.tlsdescadd} directive, AArch64
358 @item @code{.tlsdescadd}
359 Emits a TLSDESC_ADD reloc on the next instruction.
361 @cindex @code{.tlsdesccall} directive, AArch64
362 @item @code{.tlsdesccall}
363 Emits a TLSDESC_CALL reloc on the next instruction.
365 @cindex @code{.tlsdescldr} directive, AArch64
366 @item @code{.tlsdescldr}
367 Emits a TLSDESC_LDR reloc on the next instruction.
369 @c UUUUUUUUUUUUUUUUUUUUUUUUUU
371 @cindex @code{.unreq} directive, AArch64
372 @item .unreq @var{alias-name}
373 This undefines a register alias which was previously defined using the
374 @code{req} directive. For example:
381 An error occurs if the name is undefined. Note - this pseudo op can
382 be used to delete builtin in register name aliases (eg 'w0'). This
383 should only be done if it is really necessary.
385 @c VVVVVVVVVVVVVVVVVVVVVVVVVV
387 @c WWWWWWWWWWWWWWWWWWWWWWWWWW
388 @c XXXXXXXXXXXXXXXXXXXXXXXXXX
390 @cindex @code{.xword} directive, AArch64
391 @item .xword @var{expressions}
392 The @code{.xword} directive produces 64 bit values. This is the same
393 as the @code{.dword} directive.
395 @c YYYYYYYYYYYYYYYYYYYYYYYYYY
396 @c ZZZZZZZZZZZZZZZZZZZZZZZZZZ
400 @node AArch64 Opcodes
403 @cindex AArch64 opcodes
404 @cindex opcodes for AArch64
405 GAS implements all the standard AArch64 opcodes. It also
406 implements several pseudo opcodes, including several synthetic load
411 @cindex @code{LDR reg,=<expr>} pseudo op, AArch64
414 ldr <register> , =<expression>
417 The constant expression will be placed into the nearest literal pool (if it not
418 already there) and a PC-relative LDR instruction will be generated.
422 For more information on the AArch64 instruction set and assembly language
423 notation, see @samp{ARMv8 Instruction Set Overview} available at
424 @uref{http://infocenter.arm.com}.
427 @node AArch64 Mapping Symbols
428 @section Mapping Symbols
430 The AArch64 ELF specification requires that special symbols be inserted
431 into object files to mark certain features:
437 At the start of a region of code containing AArch64 instructions.
441 At the start of a region of data.