Re: test-getgroups.c:stringop-overflow warning on newer GCC

[Bernhard Voelker]

Hi Bruno,

On 1/1/21 1:56 PM, Bruno Haible wrote:
> Hi Berny,
> 
> Bernhard Voelker wrote in
> <https://lists.gnu.org/archive/html/bug-gnulib/2020-12/msg00090.html>:
>> Newer GCC complains about this test:
>>
>>   $ make test-getgroups.o V=1
>>   depbase=`echo test-getgroups.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\
>>   gcc -DHAVE_CONFIG_H -DEXEEXT=\"\" -I. -I..  -DIN_FINDUTILS_GNULIB_TESTS=1 
>> -I. -I. -I.. -I./.. -I../gl/lib -I./.. \
>>     /gl/lib   -g -O2 -MT test-getgroups.o -MD -MP -MF $depbase.Tpo -c -o 
>> test-getgroups.o test-getgroups.c &&\
>>   mv -f $depbase.Tpo $depbase.Po
>>   In file included from test-getgroups.c:31:
>>   test-getgroups.c: In function 'main':
>>   test-getgroups.c:65:11: warning: argument 1 value -1 is negative 
>> [-Wstringop-overflow=]
>>      65 |   ASSERT (getgroups (-1, NULL) == -1);
>>         |           ^~~~~~~~~~~~~~~~~~~~
> 
> I can't reproduce this with a testdir created through
>   ./gnulib-tool --create-testdir --dir=... --single-configure getgroups
> and GCC 10.2.0, even with '-Wall' (whereas the GCC invocation that you show 
> does
> not invoke any warning options!):
yes, this shows up without -Wall here.

> $ gcc -DHAVE_CONFIG_H -I. -I..  -DGNULIB_STRICT_CHECKING=1 
> -DIN_GNULIB_TESTS=1 -I. -I. -I.. -I./.. -I../gllib -I./../gllib   -g -O2 -c 
> test-getgroups.c -Wall
> (no diagnostics)

I reproduced again without -Wall both on my openSUSE Tumbleweed system with
  gcc (SUSE Linux) 10.2.1 20201202 [revision 
e563687cf9d3d1278f45aaebd03e0f66531076c9]
and on Fedora (in a docker container) with
  gcc (GCC) 10.2.1 20201125 (Red Hat 10.2.1-9)

So it may be an issue with the 10.2.1 version

> Also, it's strange that this warning reports to come from -Wstringop-overflow
> — whereas 'getgroups' is not a string operation>
> So, to me it looks like a bug in the particular GCC version that you are 
> using.
> 
> Under regular circumstances, I would consider adding a #pragma GCC diagnostic,
> as you suggest, but not under these circumstances.

I'm not sure how to proceed from here.

Have a nice day,
Berny