On Sat, Aug 03, 2024 at 10:55:07PM +0200, Thomas Weißschuh wrote:
> Aug 3, 2024 20:33:11 Willy Tarreau <w@xxxxxx>:
>
> > On Sat, Aug 03, 2024 at 08:28:08PM +0200, Thomas Weißschuh wrote:
> >>> 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 don't understand why. Above both are tested on the first line.
> > Am I missing something ?
>
> This specifically does not work [0]:
>
> a result, combining the two tests into a single expression as shown
> below would only be valid with a compiler that supports the operator but not
> with others that don't.
Ah I didn't remember about that one, thanks for the reference. Indeed
it's annoying then.
We have a similar construct in compiler.h:
#if defined(__has_attribute)
# if __has_attribute(no_stack_protector)
# define __no_stack_protector __attribute__((no_stack_protector))
# else
# define __no_stack_protector __attribute__((__optimize__("-fno-stack-protector")))
# endif
#else
# define __no_stack_protector __attribute__((__optimize__("-fno-stack-protector")))
#endif /* defined(__has_attribute) */
Maybe it would be a good opportunity to have our own macro so as to
simplify such tests:
#if defined(__has_attribute)
# define nolibc_has_attribute(x) __has_attribute(x)
#else
# define nolibc_has_attribute(x) 0
#endif
#if nolibc_has_attribute(no_stack_protector)
# define __no_stack_protector __attribute__((no_stack_protector))
#else
# define __no_stack_protector __attribute__((__optimize__("-fno-stack-protector"
#endif
Then:
#if nolibc_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
It's as you want. Either we take your #undef-based solution or we take
this opportunity to clean up as above. I'm fine with both.
Thanks!
Willy
