_FORTIFY_SOURCE=3 fail for gcc 12/glibc 2.35

[Petr Ovtchenkov]

Hi,

_FORTIFY_SOURCE=3 fail to compile with gcc 12/glibc 2.35.

Used:
  (GCC) 12.0.1 20220504 (prerelease)
  glibc ec5b79aac768 (release/2.35/master)

<snip>
In file included from ..../x86_64-unknown-linux-gnu/usr/include/features.h:490,
                 from .../x86_64-unknown-linux-gnu/usr/include/assert.h:35,
                 from elf_getarsym.c:34:
In function ‘pread’,
    inlined from ‘pread_retry’ at ../lib/system.h:188:21,
    inlined from ‘read_number_entries’ at elf_getarsym.c:63:21,
    inlined from ‘elf_getarsym’ at elf_getarsym.c:172:11:
..../x86_64-unknown-linux-gnu/usr/include/bits/unistd.h:74:10: error: ‘__pread_alias’ specified size between 9223372036854775813 and 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]
   74 |   return __glibc_fortify (pread, __nbytes, sizeof (char),
      |          ^~~~~~~~~~~~~~~
elf_getarsym.c: In function ‘elf_getarsym’:
elf_getarsym.c:56:5: note: destination object allocated here
   56 |   } u;
      |     ^
..../x86_64-unknown-linux-gnu/usr/include/bits/unistd.h:50:16: note: in a call to function ‘__pread_alias’ declared with attribute ‘access (write_only, 2, 3)’
   50 | extern ssize_t __REDIRECT (__pread_alias,
      |                ^~~~~~~~~~


In file included from ..../x86_64-unknown-linux-gnu/usr/include/features.h:490,
                 from ..../x86_64-unknown-linux-gnu/usr/include/assert.h:35,
                 from elf_getarsym.c:34:
In function ‘pread’,
    inlined from ‘pread_retry’ at ../lib/system.h:188:21,
    inlined from ‘read_number_entries’ at elf_getarsym.c:63:21,
    inlined from ‘elf_getarsym’ at elf_getarsym.c:172:11:
.../x86_64-unknown-linux-gnu/usr/include/bits/unistd.h:74:10: error: ‘__pread_alias’ specified size between 9223372036854775813 and 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]
   74 |   return __glibc_fortify (pread, __nbytes, sizeof (char),
      |          ^~~~~~~~~~~~~~~
elf_getarsym.c: In function ‘elf_getarsym’:
elf_getarsym.c:56:5: note: destination object allocated here
   56 |   } u;
      |     ^
.../x86_64-unknown-linux-gnu/usr/include/bits/unistd.h:50:16: note: in a call to function ‘__pread_alias’ declared with attribute ‘access (write_only, 2, 3)’
   50 | extern ssize_t __REDIRECT (__pread_alias,
</snip>

Lower level (_FORTIFY_SOURCE=2) compiled fine.

Tricks similar to suggested in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91397
not help: warning disappear only when I set wrong condition

  if (w >= sizeof(u))
    __builtin_unreachable();

(should be w > sizeof(u)).

--

   - ptr