https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96900
Bug ID: 96900
Summary: bogus -Warray-bounds on strlen with valid pointer
obtained from just-past-the-end
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
When a valid pointer into an array that has been derived from a past-the-end
pointer to a member array of an initialized constant struct is used in a call
to a string built-in like strlen GCC issues a bogus -Warray-bounds warning
indicating that the offset into the array is out of its bounds.
$ cat q.c && gcc -S -Wall q.c
struct S { char n, a[3]; };
const char a[3] = { 2, 1, 0 };
const struct S s = { 3, { 2, 1, 0 } };
int f (void)
{
const char *p = &a[sizeof a];
return __builtin_strlen (p - sizeof a); // no warning (good)
}
int g (void)
{
const char *p = &s.a[sizeof s.a];
return __builtin_strlen (p - sizeof s.a); // bogus -Warray-bounds
}
q.c: In function ‘g’:
q.c:15:10: warning: offset ‘1’ outside bounds of constant string
[-Warray-bounds]
15 | return __builtin_strlen (p - sizeof s.a); // bogus -Warray-bounds
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
q.c:4:16: note: ‘s’ declared here
4 | const struct S s = { 3, { 2, 1, 0 } };
| ^
