Implement C23 memset_explicit (bug 32378)

[Collin Funk]

Joseph Myers <josmyers@redhat.com> writes:

> On Fri, 26 Sep 2025, Paul Eggert wrote:
>
>> On 2025-09-26 12:39, Joseph Myers wrote:
>> > Although the function is only declared here for __GLIBC_USE (ISOC23),
>> > there's a reasonable argument for making it more widely available by
>> > inclusion in __USE_MISC.
>> 
>> If I'm reading the source code correctly, FreeBSD makes memset_visible in
>> <string.h> by default; you must define a strict-conformance-to-old-standards
>> macro like _ANSI_SOURCE, _C99_SOURCE or _C11_SOURCE to make it vanish.
>> 
>> Shouldn't we do something similar? I'm not seeing the point of being shy here.
>
> That's a key question for review of this patch.  Should it be visible for 
> __USE_MISC as well as __GLIBC_USE (ISOC23)?

My thinking is that we should use __USE_MISC if the C23 function was
based on an existing implementation of the function. If it was first
introduced by the C23 standard, not an existing extension, then I think
__GLIBC_USE (ISOC23) makes more sense.

I'll review the patch later though and take some time to think about
that.

Thanks for the clarification on the Clang issue, BTW.

Collin