https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92813
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic,
| |missed-optimization
Blocks| |83819
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Implementing this optimization will also make it possible to detect buffer
overflow in such cases:
$ cat t.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout t.c
char a[8];
void f (void)
{
__builtin_strcpy (a, "1234");
__builtin_sprintf (a + 4, "%s", "5678"); // warning (good)
}
void g (void)
{
__builtin_sprintf (a, "%s", "1234");
__builtin_strcat (a, "5678"); // missing warning
}
t.c: In function ‘f’:
t.c:6:32: warning: ‘__builtin_sprintf’ writing a terminating nul past the end
of the destination [-Wformat-overflow=]
6 | __builtin_sprintf (a + 4, "%s", "5678"); // warning (good)
| ^
t.c:6:3: note: ‘__builtin_sprintf’ output 5 bytes into a destination of size 4
6 | __builtin_sprintf (a + 4, "%s", "5678"); // warning (good)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
;; Function f (f, funcdef_no=0, decl_uid=1931, cgraph_uid=1, symbol_order=1)
f ()
{
<bb 2> [local count: 1073741824]:
__builtin_memcpy (&a, "1234", 5);
__builtin_sprintf (&MEM <char[8]> [(void *)&a + 4B], "%s", "5678"); [tail
call]
return;
}
;; Function g (g, funcdef_no=1, decl_uid=1934, cgraph_uid=2, symbol_order=2)
g ()
{
long unsigned int _3;
char[8] * _4;
<bb 2> [local count: 1073741824]:
__builtin_memcpy (&a, "1234", 5);
_3 = __builtin_strlen (&a);
_4 = &a + _3;
__builtin_memcpy (_4, "5678", 5); [tail call]
return;
}
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83819
[Bug 83819] [meta-bug] missing strlen optimizations
