[Bug tree-optimization/85259] [8 Regression] Missing -Wstringop-overflow= since r256683

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85259

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-04-06
     Ever confirmed|0                           |1

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
With -Wno-system-headers GCC 8 prints:

In file included from /usr/include/string.h:635,
                 from pr85259.c:1:
In function ‘strcat’,
    inlined from ‘main’ at pr85259.c:8:3:
/usr/include/bits/string3.h:148:10: warning: ‘__builtin___memcpy_chk’ forming
offset [7, 13] is out of the bounds [0, 6] of object ‘buf’ with type ‘char[6]’
[-Warray-bounds]
   return __builtin___strcat_chk (__dest, __src, __bos (__dest));
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr85259.c: In function ‘main’:
pr85259.c:3:6: note: ‘buf’ declared here
 char buf[6];
      ^~~

This is better but it's a warning for the strcat call while there should be a
warning for the strcpy() call first because it overflows the buffer.  A bug in
handle_builtin_strcpy() in tree-ssa-strlen causes GCC to miss this case.  So
there are two bugs in play here: the system header suppression and the
detection of strcpy overflow with a string literal.