[libc-coord] Add new ABI '__memcmpeq()' to libc

[Richard Biener]

On Thu, Sep 16, 2021 at 10:36 PM Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Thu, 16 Sep 2021, Chris Kennelly wrote:
>
> > In terms of relying on the feature:  If __memcmpeq is ever exposed as an a
> > simple alias for memcmp (since the notes mention that it's a valid
> > implementation), does that open up the possibility of depending on the
> > bcmp-like behavior that we were trying to escape?
>
> The proposal is as an ABI only (compilers would generate calls to
> __memcmpeq from boolean uses of memcmp, users wouldn't write calls to
> __memcmpeq directly, __memcmpeq wouldn't be declared in installed libc
> headers).  If such dependence arises, that would suggest a compiler bug
> wrongly generating such calls for non-boolean memcmp uses.

So the compiler would emit a call to __memcmpeq and at the same time
emit a weak alias of __memcmpeq to memcmp so the program links
when the libc version targeted does not provide __memcmpeq?  Or would
glibc through <string.h> magically communicate the availability of the new ABI
without actually declaring the function?
(I'm not sure whether a GCC build-time decision via configure is the
very best idea)

Richard.

> --
> Joseph S. Myers
> joseph@codesourcery.com