https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100401
Bug ID: 100401
Summary: Bogus -Wformat-overflow warning
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: lavr at ncbi dot nlm.nih.gov
Target Milestone: ---
$ gcc --version
gcc (GCC) 10.2.0
$ cat bogus.c
#include <stdio.h>
#define RECLEN 128
struct S {
int code;
char text[0];
};
const void fun(int n)
{
union {
struct S s;
char rec[RECLEN];
} x;
const char* err;
if (!n) {
err = "No error";
} else {
sprintf(x.s.text, "Error %d", n);
err = x.s.text;
}
printf("%s\n", err);
}
int main(int argc, const char* argv[])
{
fun(argc);
return 0;
}
$ gcc -Wall -O2 bogus.c
bogus.c: In function ‘fun’:
bogus.c:22:28: warning: ‘Error ’ directive writing 6 bytes into a region of
size 0 [-Wformat-overflow=]
22 | sprintf(x.s.text, "Error %d", n);
| ^~~~~~
bogus.c:22:9: note: ‘sprintf’ output between 8 and 18 bytes into a destination
of size 0
22 | sprintf(x.s.text, "Error %d", n);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
