[PATCH] Declare __warn_memset_zero_len internally for newer gcc [bz #25399]

[Florian Weimer]

* Serge Guelton:

> On Tue, Nov 03, 2020 at 04:05:11PM +0100, Florian Weimer wrote:
>> * Siddhesh Poyarekar via Libc-alpha:
>> 
>> > The __warn_memset_zero_len symbol, used to issue a linker warning
>> > about zero length memset calls, is included in warning-nop.o only when
>> > glibc is built with an older gcc, which is incorrect.  When a program
>> > calling memset with zero length is built with either gcc < 5.0 or with
>> > clang (which advertises __GNUC__ as 4), it results in a link failure
>> > due to not finding the symbol in libc_nonshared.a.
>> >
>> > Fill in this gap by declaring __warn_memset_zero_len for newer gcc as
>> > well so that it is always available in libc_nonshared.a for any
>> > compiler to link against.
>> 
>> Does Clang have its own warning for this?
>
> Clang has -Wmemset-transposed-args. The warning is emitted during smeantic
> analysis, catching two patterns: 1. a size argument of 0 and 2. when the
> constant argument is a sizeof

Is it enabled by -Wall?

Thanks,
Florian
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