https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79257
Bug ID: 79257
Summary: spurious -Wformat-overflow=1 warning with -O2 and
sanitizer
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent-gcc at vinc17 dot net
Target Milestone: ---
With r244974, on the following C code:
#include <stdio.h>
void a (void);
int main (void)
{
char buffer[2];
int i;
for (i = 0; i < 2; i++)
{
if (i == 0)
a ();
sprintf (buffer, "%d", i);
}
return 0;
}
I get:
cventin:~> =gcc -O2 -Wformat-overflow=1 -fsanitize=undefined -c tst.c
tst.c: In function ‘main’:
tst.c:14:25: warning: ‘%d’ directive writing between 1 and 10 bytes into a
region of size 2 [-Wformat-overflow=]
sprintf (buffer, "%d", i);
^~
tst.c:14:24: note: directive argument in the range [0, 2147483646]
sprintf (buffer, "%d", i);
^~~~
tst.c:14:7: note: ‘sprintf’ output between 2 and 11 bytes into a destination of
size 2
sprintf (buffer, "%d", i);
^~~~~~~~~~~~~~~~~~~~~~~~~
tst.c:14:25: warning: ‘%d’ directive writing between 1 and 10 bytes into a
region of size 2 [-Wformat-overflow=]
sprintf (buffer, "%d", i);
^~
tst.c:14:24: note: directive argument in the range [0, 2147483646]
sprintf (buffer, "%d", i);
^~~~
tst.c:14:7: note: ‘sprintf’ output between 2 and 11 bytes into a destination of
size 2
sprintf (buffer, "%d", i);
^~~~~~~~~~~~~~~~~~~~~~~~~
If I remove any of -O2, -Wformat-overflow=1 or -fsanitize=undefined, I no
longer get a warning. Ditto if I remove the test on i or the call to a().
Note: I've found this bug when building the MPFR tests (tl2b.c).
