https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95988
Bug ID: 95988
Summary: [10/11 Regression] Bogus
-Warray-bounds/-Wstringop-overflow warning with loop
Product: gcc
Version: 10.0
Status: NEW
Keywords: diagnostic
Severity: normal
Priority: P2
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
CC: msebor at gcc dot gnu.org
Depends on: 94655
Target Milestone: 10.2
Target Milestone: 10.2
CC: msebor at gcc dot gnu.org
Last reconfirmed: 2020-06-30
Status: NEW
Priority: P2
Ever confirmed: 1
Depends on: 94655
Compile with -O2 -W -Wall:
void f(int*);
void g(int*);
struct sched_group_t {
int lock;
struct {
char name[32 + 1];
int aa;
} group[(3 + 9)];
} ;
struct sched_global_t {
char t[(3 + 9)][3];
struct sched_group_t sched_group;
};
struct sched_global_t *sched_global;
int hh(const char *name)
{
struct sched_group_t *sched_group = &sched_global->sched_group;
int i;
g(&sched_group->lock);
for (i = 3; i < (3 + 9); i++) {
if (!sched_group->group[i].aa)
{
char *grp_name = sched_group->group[i].name;
__builtin_strncpy(grp_name, name, 32 - 1);
grp_name[32 - 1] = 0;
break;
}
}
f(&sched_group->lock);
return 0;
}
--- CUT ---
t.c: In function ‘hh’:
t.c:28:5: warning: ‘__builtin_strncpy’ offset [124, 484] is out of the bounds
[0, 4] [-Warray-bounds]
28 | __builtin_strncpy(grp_name, name, 32 - 1);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
t.c:29:22: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
29 | grp_name[32 - 1] = 0;
| ~~~~~~~~~~~~~~~~~^~~
t.c:4:7: note: at offset 155 to object ‘lock’ with size 4 declared here
4 | int lock;
| ^~~~
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The problem is related to &sched_global->sched_group and
&sched_global->sched_group->lock are at the same location, so GCC seems to
select the MEM for &sched_global->sched_group->lock for both. THIS is just a
diagnostic issue of the warning.
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note unlike other -Warray-bounds/-Wstringop-overflow warnings, there is no
flexiable array in effect here. Rather it is due to using the offset for
sched_global->sched_group and sched_global->sched_group.lock issue.
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I should mention this was reduced from upstream ODP
(https://opendataplane.org/) Linux generic version.
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is related to PR 94655.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94655
[Bug 94655] [10/11 Regression] Implicit assignment operator triggers
stringop-overflow warning since r10-5451-gef29b12cfbb4979a
