[PATCH] avoid bogus -Wstringop-overflow for strncpy with _FORTIFY_SOURCE (PR 82646)

[Christophe Lyon]

On 7 December 2017 at 20:28, Martin Sebor <msebor@gmail.com> wrote:
> On 12/07/2017 06:46 AM, Christophe Lyon wrote:
>>
>> Hi Martin,
>>
>>
>> On 6 December 2017 at 00:51, Jeff Law <law@redhat.com> wrote:
>>>
>>> On 12/05/2017 04:47 PM, Martin Sebor wrote:
>>>>
>>>> PR middle-end/82646 - bogus -Wstringop-overflow with
>>>> -D_FORTIFY_SOURCE=2 on strncpy with range to a member array,
>>>>
>>>> The bug points out a false positive in a call to strncpy() when
>>>> _FORTIFY_SOURCE is defined that doesn't exist otherwise.
>>>>
>>>> The problem is that __builtin_strncpy buffer overflow checking
>>>> is done along with the expansion of the intrinsic in one place
>>>> and __builtin___strncpy_chk is handled differently in another,
>>>> and the two are out of sync.
>>>>
>>>> The attached patch corrects the choice of arguments used for
>>>> overflow detection in __builtin___strncpy_chk and aligns
>>>> the diagnostics between the two intrinsics.
>>>>
>>>> Martin
>>>>
>>>> gcc-82646.diff
>>>>
>>>>
>>>> PR tree-optimization/82646 - bogus -Wstringop-overflow with
>>>> -D_FORTIFY_SOURCE=2 on strncpy with range to a member array
>>>>
>>>> gcc/ChangeLog:
>>>>
>>>>       PR tree-optimization/82646
>>>>       * builtins.c (maybe_emit_chk_warning): Use size as the bound for
>>>>       strncpy, not maxlen.
>>>>
>>>> gcc/testsuite/ChangeLog:
>>>>
>>>>       PR tree-optimization/82646
>>>>       * gcc.dg/builtin-stringop-chk-1.c: Adjust.
>>>>       * gcc.dg/builtin-stringop-chk-9.c: New test.
>>>
>>> OK.
>>>
>>
>> The new test fails on 32 bits platforms (arm, x86_32, aarch64 ilp32):
>> FAIL:    gcc.dg/builtin-stringop-chk-9.c  (test for warnings, line 125)
>> FAIL:    gcc.dg/builtin-stringop-chk-9.c  (test for warnings, line 133)
>> FAIL:    gcc.dg/builtin-stringop-chk-9.c  (test for warnings, line 141)
>> FAIL:    gcc.dg/builtin-stringop-chk-9.c  (test for warnings, line 149)
>
>
> I believe these failures were due to bug 83296 that Richard fixed
> earlier today.  With the change in my tree, the test passes for
> me with the arm-linux-gnueabi cross-compiler.  Can you please
> try again and let me know if the failures persist on any of your
> targets?
>

Indeed I can see it was fixed between r255460 and r255467,
and Richard's patch is in the range (r255466).

Thanks,

Christophe

> Thanks
> Martin