Aug 3, 2024 11:26:07 Willy Tarreau w@1wt.eu:
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@weissschuh.net
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.