https://sourceware.org/bugzilla/show_bug.cgi?id=25750
--- Comment #10 from Fangrui Song <i at maskray dot me> ---
(In reply to Jian Cai from comment #8)
Hi Jian,
> I did however find a variation that worked and did not have any behavioural
> inconsistencies:
For
.macro memorize a
\a
.endm
memorize .long (19371226)
The x86 backend rejects it while most other backends accept it. This is
actually unintentional.
gas/config/tc-i386.c defines
/* List of chars besides those in app.c:symbol_chars that can start an
operand. Used to prevent the scrubber eating vital white-space. */
const char extra_symbol_chars[] = "*%-([{}"
The type of these symbols are considered LEX_IS_SYMBOL_COMPONENT.
Before the input is fed to the parser, gas runs do_scrub_chars() to perform
some preprocessing.
* For other backends, lex['('] is 0, even though the state is 10, no space is
kept
macro_expand() will see `.long(19371226)` and the string will be parsed as an
argument.
* For the x86 backend, lex['('] is LEX_IS_SYMBOL_COMPONENT, the space before
'(' is kept (state is 10).
macro_expand() will see `.long (19371226)` and the string will be parsed as
two arguments.
If the argument does not have the `:vararg` qualifier, gas will error
`Error: too many positional arguments`
There is one feature not documented in
https://sourceware.org/binutils/docs/as/Macro.html
For a string literal argument, gas will remove the quotes when evaluation the
argument.
This makes the following example work:
.macro foo a
\a
.endm
foo ".section sec"
For the Linux kernel, __emit_insn may be used as either a directive or an
operand.
Its reliance on `.inst (x)` being parsed as a whole is brittle.
arch/arm64/include/asm/sysreg.h
52:#define __emit_inst(x) .inst (x)
arch/arm64/include/asm/sysreg.h
93:#define SET_PSTATE_PAN(x) __emit_inst(0xd500401f | PSTATE_PAN |
((!!x) << PSTATE_Imm_shift))
arch/arm64/kvm/hyp/entry.S
112: ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN)
#define __emit_inst(x) .inst(x)
may be the most suitable workaround for clang integrated assembler.
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