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SubjectRe: [PATCH v2 4/6] compiler-gcc.h: add asm_inline definition
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On 05/09/2019 02.18, Nick Desaulniers wrote:
> On Fri, Aug 30, 2019 at 4:15 PM Rasmus Villemoes
> <linux@rasmusvillemoes.dk> wrote:
>>
>> This adds an asm_inline macro which expands to "asm inline" [1] when gcc
>> is new enough (>= 9.1), and just asm for older gccs and other
>> compilers.
>>
>> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
>> ---
>> include/linux/compiler-gcc.h | 4 ++++
>> include/linux/compiler_types.h | 4 ++++
>> 2 files changed, 8 insertions(+)
>>
>> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
>> index d7ee4c6bad48..544b87b41b58 100644
>> --- a/include/linux/compiler-gcc.h
>> +++ b/include/linux/compiler-gcc.h
>> @@ -172,3 +172,7 @@
>> #endif
>>
>> #define __no_fgcse __attribute__((optimize("-fno-gcse")))
>> +
>> +#if GCC_VERSION >= 90100
>
> Is it too late to ask for a feature test macro? Maybe one already
> exists?

No, not as far as I know. Perhaps something like below, though that
won't affect the already released gcc 9.1 and 9.2, of course.

gcc maintainers, WDYT? Can we add a feature test macro for asm inline()?
For context, I'm trying to add an asm_inline macro to the kernel source
that will fall back to asm when "asm inline" is not supported - see
https://lore.kernel.org/lkml/20190830231527.22304-1-linux@rasmusvillemoes.dk/
for the whole thread.

From: Rasmus Villemoes <rv@rasmusvillemoes.dk>
Subject: [PATCH] add feature test macro for "asm inline"

Allow users to check availability of "asm inline()" via a feature test
macro. If and when clang implements support for "asm inline()", it's
easier for users if they can just test __HAVE_ASM_INLINE rather than
juggling different version checks for different compilers.

Changelog:

gcc/c-family/

* c-cppbuiltin.c (c_cpp_builtins): Add pre-define for
__HAVE_ASM_INLINE.

gcc/

* doc/cpp.texi: Document predefine __HAVE_ASM_INLINE.
---
gcc/c-family/c-cppbuiltin.c | 3 +++
gcc/doc/cpp.texi | 5 +++++
2 files changed, 8 insertions(+)

diff --git a/gcc/c-family/c-cppbuiltin.c b/gcc/c-family/c-cppbuiltin.c
index fc68bc4d0c4..163f3058741 100644
--- a/gcc/c-family/c-cppbuiltin.c
+++ b/gcc/c-family/c-cppbuiltin.c
@@ -1383,6 +1383,9 @@ c_cpp_builtins (cpp_reader *pfile)
if (targetm.have_speculation_safe_value (false))
cpp_define (pfile, "__HAVE_SPECULATION_SAFE_VALUE");

+ /* Show the availability of "asm inline()". */
+ cpp_define (pfile, "__HAVE_ASM_INLINE");
+
#ifdef DWARF2_UNWIND_INFO
if (dwarf2out_do_cfi_asm ())
cpp_define (pfile, "__GCC_HAVE_DWARF2_CFI_ASM");
diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi
index e271f5180d8..98f6d625857 100644
--- a/gcc/doc/cpp.texi
+++ b/gcc/doc/cpp.texi
@@ -2386,6 +2386,11 @@ and swap operations on operands 1, 2, 4, 8 or 16
bytes in length, respectively.
This macro is defined with the value 1 to show that this version of GCC
supports @code{__builtin_speculation_safe_value}.

+@item __HAVE_ASM_INLINE
+This macro is defined with the value 1 to show that this version of GCC
+supports @code{asm inline()}. @xref{Size of an asm,,, gcc, Using
+the GNU Compiler Collection (GCC)}.
+
@item __GCC_HAVE_DWARF2_CFI_ASM
This macro is defined when the compiler is emitting DWARF CFI directives
to the assembler. When this is defined, it is possible to emit those same
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