Re: scratch/igc warning

[Andrea Corallo]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Andrea Corallo <acorallo@gnu.org> writes:
>
>> Hi,
>>
>> GCC 12.3 is giving me this warning building scratch/igc:
>>
>> ========
>>   CC       xfaces.o
>> In file included from /usr/include/string.h:535,
>>                  from ../lib/string.h:41,
>>                  from lisp.h:29,
>>                  from xfaces.c:226:
>> In function ‘memset’,
>>     inlined from ‘make_realized_face’ at xfaces.c:4581:3,
>>     inlined from ‘realize_gui_face’ at xfaces.c:6214:10,
>>     inlined from ‘realize_face’ at xfaces.c:6124:12:
>> /usr/include/x86_64-linux-gnu/bits/string_fortified.h:59:10: warning: 
>> ‘__builtin_memset’ offset [164, 303] from the object at ‘face’ is out of the 
>> bounds of referenced subobject ‘id’ with type ‘int’ at offset 160 
>> [-Warray-bounds]
>>    59 |   return __builtin___memset_chk (__dest, __ch, __len,
>>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>    60 |                                  __glibc_objsize0 (__dest));
>>       |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~
>> In file included from termhooks.h:27,
>>                  from frame.h:22,
>>                  from xfaces.c:229:
>> dispextern.h: In function ‘realize_face’:
>> dispextern.h:1730:7: note: subobject ‘id’ declared here
>>  1730 |   int id;
>>       |       ^~
>> In function ‘memset’,
>>     inlined from ‘make_realized_face’ at xfaces.c:4581:3,
>>     inlined from ‘realize_tty_face’ at xfaces.c:6641:10,
>>     inlined from ‘realize_face’ at xfaces.c:6126:12:
>> /usr/include/x86_64-linux-gnu/bits/string_fortified.h:59:10: warning: 
>> ‘__builtin_memset’ offset [164, 303] from the object at ‘face’ is out of the 
>> bounds of referenced subobject ‘id’ with type ‘int’ at offset 160 
>> [-Warray-bounds]
>>    59 |   return __builtin___memset_chk (__dest, __ch, __len,
>>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>    60 |                                  __glibc_objsize0 (__dest));
>>       |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~
>> dispextern.h: In function ‘realize_face’:
>> dispextern.h:1730:7: note: subobject ‘id’ declared here
>>  1730 |   int id;
>>       |       ^~
>> In function ‘memset’,
>>     inlined from ‘make_realized_face’ at xfaces.c:4581:3,
>>     inlined from ‘realize_face’ at xfaces.c:6130:14:
>> /usr/include/x86_64-linux-gnu/bits/string_fortified.h:59:10: warning: 
>> ‘__builtin_memset’ offset [164, 303] from the object at ‘face’ is out of the 
>> bounds of referenced subobject ‘id’ with type ‘int’ at offset 160 
>> [-Warray-bounds]
>>    59 |   return __builtin___memset_chk (__dest, __ch, __len,
>>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>    60 |                                  __glibc_objsize0 (__dest));
>>       |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~
>> dispextern.h: In function ‘realize_face’:
>> dispextern.h:1730:7: note: subobject ‘id’ declared here
>>  1730 |   int id;
>>       |       ^~
>> ========
>>
>> ATM don't know if it's a real issue or a false positive so I thought was
>> worth mentioning.
>
> Hm, that's this one, right?
>
>   static struct face *
>   make_realized_face (Lisp_Object *attr)
>   {
>     enum { off = offsetof (struct face, id) };
>   #ifdef HAVE_MPS
>     struct face *face = igc_make_face ();
>   #else
>     struct face *face = xmalloc (sizeof *face);
>   #endif
>     memcpy (face->lface, attr, sizeof face->lface);
>     memset (&face->id, 0, sizeof *face - off);
>     face->ascii_face = face;
>
>     return face;
>   }
>
> which we can rewrite, for MPS
>
>   static struct face *
>   make_realized_face (Lisp_Object *attr)
>   {
>   #ifdef HAVE_MPS
>     struct face *face = igc_make_face ();
>     memcpy (face->lface, attr, sizeof face->lface);
>   #else
>     enum { off = offsetof (struct face, id) };
>     struct face *face = xmalloc (sizeof *face);
>     memcpy (face->lface, attr, sizeof face->lface);
>     memset (&face->id, 0, sizeof *face - off);
>   #endif
>     face->ascii_face = face;
>
>     return face;
>   }
>
> because igc returns something zero-initialized anyway. (I'll do that.).

Yep this clean the warning!

> But I wonder - does GCC 12 also complain for the non-MPS case?

It does not, my other tracked branches (master and emacs-30) are now
warning clean here with similar configurations.

With this fix scratch/igc will be warning clean as well 😀

Thanks

  Andrea