Avoid array-bounds warning in testsuite on i586

  gcc-6 is complaining about this, breaking the testsuite run:

In file included from ../string/string.h:627:0,
                 from ../include/string.h:54,
                 from tester.c:32,
                 from inl-tester.c:6:
tester.c: In function 'test_strncat':
../sysdeps/x86/bits/string.h:1092:3: error: array subscript is below array bounds [-Werror=array-bounds]
   --__tmp;
   ^~~~~~~

I don't see any other way to avoid the warning.

Andreas.

	[BZ #20260]
	* sysdeps/i386/Makefile (CFLAGS-inl-tester.c): Define.
	* string/Makefile (CFLAGS-inl-tester.c, CFLAGS-noinl-tester.c)
	(CFLAGS-tst-strlen.c, CFLAGS-stratcliff.c, CFLAGS-test-ffs.c)
	(CFLAGS-tst-inlcall.c): Append value.
---
 string/Makefile       | 12 ++++++------
 sysdeps/i386/Makefile |  4 ++++
 2 files changed, 10 insertions(+), 6 deletions(-)
  

On 06/29/2016 11:08 AM, Andreas Schwab wrote:
> gcc-6 is complaining about this, breaking the testsuite run:
>
> In file included from ../string/string.h:627:0,
>                  from ../include/string.h:54,
>                  from tester.c:32,
>                  from inl-tester.c:6:
> tester.c: In function 'test_strncat':
> ../sysdeps/x86/bits/string.h:1092:3: error: array subscript is below array bounds [-Werror=array-bounds]
>    --__tmp;
>    ^~~~~~~
>
> I don't see any other way to avoid the warning.

We could move the decrement operation into the assembly part, where GCC 
cannot see it.  Or we could cast to uintptr_t before subtracting 1.

> +# Suppress array bounds warning from strncat macro in
> +# sysdeps/x86/bits/string.h when building for i[345]86
> +CFLAGS-inl-tester.c += -Wno-array-bounds

It's triggered by an installed header, so this does not fix the bug at 
all.  I expect applications run into the warning as well.

Thanks,
Florian
  

Florian Weimer <fweimer@redhat.com> writes:

> It's triggered by an installed header, so this does not fix the bug at
> all.  I expect applications run into the warning as well.

Only if compiled with -Wsystem-headers.

Andreas.
  

On 06/29/2016 01:58 PM, Andreas Schwab wrote:
> Florian Weimer <fweimer@redhat.com> writes:
>
>> It's triggered by an installed header, so this does not fix the bug at
>> all.  I expect applications run into the warning as well.
>
> Only if compiled with -Wsystem-headers.

I would expect that this could trip ubsan as well.

Florian