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
What do you think ?
Willy
