Re: [testsuite, committed] Compile strncpy-fix-1.c with -Wno-stringop-truncation

[Martin Sebor <msebor at gmail dot com>]

On 11/15/2017 08:12 AM, Tom de Vries wrote:
> [ Re: [PATCH 3/4] enhance overflow and truncation detection in strncpy
> and strncat (PR 81117) ]
>
> On 08/06/2017 10:07 PM, Martin Sebor wrote:
> > Part 3 of the series contains the meat of the patch: the new
> > -Wstringop-truncation option, and enhancements to -Wstringop-
> > overflow, and -Wpointer-sizeof-memaccess to detect misuses of
> > strncpy and strncat.
> >
> > Martin
> >
> > gcc-81117-3.diff
> >
> >
> > PR c/81117 - Improve buffer overflow checking in strncpy
>
> > gcc/testsuite/ChangeLog:
> >
> >     PR c/81117
> >     * c-c++-common/Wsizeof-pointer-memaccess3.c: New test.
> >     * c-c++-common/Wstringop-overflow.c: Same.
> >     * c-c++-common/Wstringop-truncation.c: Same.
> >     * c-c++-common/Wsizeof-pointer-memaccess2.c: Adjust.
> >     * c-c++-common/attr-nonstring-2.c: New test.
> >     * g++.dg/torture/Wsizeof-pointer-memaccess1.C: Adjust.
> >     * g++.dg/torture/Wsizeof-pointer-memaccess2.C: Same.
> >     * gcc.dg/torture/pr63554.c: Same.
> >     * gcc.dg/Walloca-1.c: Disable macro tracking.
>
> Hi,
>
> this also caused a regression in strncpy-fix-1.c. I noticed it for nvptx
>  (but I also saw it in other test results, f.i. for
> x86_64-unknown-freebsd12.0 at
> https://gcc.gnu.org/ml/gcc-testresults/2017-11/msg01276.html ).
>
> On linux you don't see this unless you add -Wsystem-headers:

Yes, some Glibc versions (I think 2.24 and prior) define strncpy
as a macro.  The macro has been removed from newer versions, which
makes the warning show up inconsistently.  I test on Fedora 25 with
the older Glibc so I don't see all these warnings.

I'm tracking the problem bug 82944.

> ...
> $ gcc src/gcc/testsuite/gcc.dg/strncpy-fix-1.c
> -fno-diagnostics-show-caret -fdiagnostics-color=never -O2 -Wall
> -Wsystem-headers -S -o strncpy-fix-1.s
> In file included from /usr/include/string.h:630,
>                  from src/gcc/testsuite/gcc.dg/strncpy-fix-1.c:6:
> src/gcc/testsuite/gcc.dg/strncpy-fix-1.c: In function ‘f’:
> src/gcc/testsuite/gcc.dg/strncpy-fix-1.c:10:3: warning:
> ‘__builtin_strncpy’ output truncated before terminating nul copying 2
> bytes from a string of the same length [-Wstringop-truncation]
> ...
>
> Fixed by adding -Wno-stringop-truncation.
>
> Committed as obvious.

Thanks
Martin