[PATCH] x86-64 memcmp: Use unsigned Jcc instructions on size

[Florian Weimer]

* H. J. Lu:

> Since the size argument is unsigned. we should use unsigned Jcc
> instructions, instead of signed to check size.
>
> Tested on x86-64 and x32, with and without --disable-multi-arch.

Does this impact x86-64 at all (technically), consider that an object
size larger than SSIZE_MAX would be undefined anyway?

It seems that on x32, it can give incorrect results if the sign bit on
the 64-bit register is set.  In this sense, it is similar to
CVE-2019-6488 in impact, right?  If we decide to treat this as a
security vulnerability, we need a new CVE ID because the version range
is different (bug 24155 was not fixed in the 2.29 release).

Thanks,
Florian