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Message-ID: <CAFiYyc0nghZMYdhO9T2h92oOZtnxTHUikhgw46Gp9mme5_nVvA@mail.gmail.com>
Date: Fri, 17 Sep 2021 09:43:55 +0200
From: Richard Biener <richard.guenther@...il.com>
To: Joseph Myers <joseph@...esourcery.com>
Cc: libc-coord@...ts.openwall.com, GCC Development <gcc@....gnu.org>,
GNU C Library <libc-alpha@...rceware.org>
Subject: Re: Add new ABI '__memcmpeq()' to libc
On Thu, Sep 16, 2021 at 10:36 PM Joseph Myers <joseph@...esourcery.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@...esourcery.com
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