Aug 3, 2024 11:26:07 Willy Tarreau <w@xxxxxx>:
> On Sun, Jul 28, 2024 at 12:09:58PM +0200, Thomas Weißschuh wrote:
>> The current entrypoint attributes optimize("Os", "omit-frame-pointer")
>> are intended to avoid all compiler generated code, like function
>> porologue and epilogue.
>> This is the exact usecase implemented by the attribute "naked".
>>
>> Unfortunately this is not implemented by GCC for all targets,
>> so only use it where available.
>> This also provides compatibility with clang, which recognizes the
>> "naked" attribute but not the previously used attribute "optimized".
>>
>> Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
>> ---
>> tools/include/nolibc/compiler.h | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/tools/include/nolibc/compiler.h b/tools/include/nolibc/compiler.h
>> index fe3701863634..f77bb7d3e1a8 100644
>> --- a/tools/include/nolibc/compiler.h
>> +++ b/tools/include/nolibc/compiler.h
>> @@ -9,6 +9,15 @@
>> #define __entrypoint __attribute__((optimize("Os", "omit-frame-pointer")))
>> #define __entrypoint_epilogue() __builtin_unreachable()
>>
>> +#if defined(__has_attribute)
>> +# if __has_attribute(naked)
>> +# undef __entrypoint
>> +# define __entrypoint __attribute__((naked))
>> +# undef __entrypoint_epilogue
>> +# define __entrypoint_epilogue()
>> +# endif
>> +#endif /* defined(__has_attribute) */
>
> I would find it cleaner to enclose the previous declaration with the #if
> rather than #undef everything just after it has been defined. Also it's
> not very common to undo declarations just after they've been done, and
> it makes quick code analysis harder.
>
> I think that it can resolve to roughly this:
>
> #if defined(__has_attribute) && __has_attribute(naked)
> # define __entrypoint __attribute__((naked))
> # define __entrypoint_epilogue()
> #else
> # define __entrypoint __attribute__((optimize("Os", "omit-frame-pointer")))
> # define __entrypoint_epilogue() __builtin_unreachable()
> #endif
We would need to duplicate the define for the
!defined(__has_attribute) case.
I wanted to avoid that duplication.
> What do you think ?
With the reasoning above I'll let you choose.
