https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101415
Bug ID: 101415
Summary: [12 Regression] Bogus -Warray-bounds warning with
stpcpy
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: fw at gcc dot gnu.org
Target Milestone: ---
This (derived from the glibc function of the same name):
char *
nis_local_group (char *cptr)
{
static char __nisgroup[1025];
if (*cptr != '\0' && __builtin_strlen (cptr) < 1024)
{
char *cp = __builtin_stpcpy (__nisgroup, cptr);
if (cp[-1] != '.')
__builtin_abort ();
}
return __nisgroup;
}
results in
/tmp/t.c: In function ‘nis_local_group’:
/tmp/t.c:10:13: error: array subscript -1 is outside array bounds of
‘char[1025]
’ [-Werror=array-bounds]
10 | if (cp[-1] != '.')
| ~~^~~~
/tmp/t.c:4:15: note: at offset -1 into object ‘__nisgroup’ of size 1025
4 | static char __nisgroup[1025];
| ^~~~~~~~~~
with -O2 -Wall on x86-64 gcc version 12.0.0 20210711 (experimental) [master
revision :97a8a2829:269256f33c51222167ad461f775d5468bb5ecaf5].
The warning is bogus because stpcpy returns a pointer to the NUL byte, which is
not at the first byte of __nisgroup after the stpcpy. The glibc original does
not have this check, so it is buggy, but the warning seems overly aggressive if
it cannot detect non-empty strings for stpcpy.
