https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100403
Bug ID: 100403
Summary: Bogus "function may return address of local variable"
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 test.c
#include <stdio.h>
#include <string.h>
#define RECLEN 128
struct R {
int head;
int code;
char text[1];
};
const char* fun(int n, const struct R* p)
{
union {
struct R r;
char rec[RECLEN];
} x;
const char* err = 0;
memset(&x, 0, sizeof(x));
if (p)
memcpy(&x.r, p, sizeof(*p));
else
err = "Invalid argument";
if (!err) {
static const char magic[] = "MAGIC";
const char* msg;
if (memcmp(x.rec, magic, sizeof(magic)-1) == 0)
msg = x.rec;
else if (x.r.text[0])
msg = x.r.text;
else
msg = "Error w/code";
if (msg)
printf("%s\n", msg);
if (x.rec <= msg && msg < x.rec + sizeof(x))
err = "Error detected";
else
err = msg;
} else
printf("%s\n", err);
return err;
}
$ gcc -Wall -O2 -c test.c
test.c: In function ‘fun’:
test.c:45:12: warning: function may return address of local variable
[-Wreturn-local-addr]
45 | return err;
| ^~~
test.c:19:7: note: declared here
19 | } x;
| ^
test.c:19:7: note: declared here
Noted that does not matter whether "sizeof(x)" or "sizeof(x.rec)" is used at
the end of the "if()" statement on line 39.
