https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103835
Bug ID: 103835
Summary: Bogus sprintf warnings
Product: gcc
Version: 11.2.0
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: ---
Please address these warnings because they create more noise than they help!
$ cat test.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
const char* fun(char* buf, const char* pfx, int a, int b)
{
sprintf(buf, "%sa = %d\n"
"%sb = %d\n",
pfx, a, pfx, b);
return buf;
}
int main(int argc, char* argv[])
{
char buf[500];
const char* str;
strcpy(buf, "\t");
str = fun(buf + strlen(buf) + 1, buf, atoi(argv[1]), atoi(argv[2]));
printf("%s\n", str);
return 0;
}
$ gcc --version
gcc (GCC) 11.2.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ gcc -Wall -O6 test.c
test.c: In function ‘main’:
test.c:8:21: warning: ‘a = ’ directive writing 4 bytes into a region of size
between 0 and 499 [-Wformat-overflow=]
8 | sprintf(buf, "%sa = %d\n"
| ^~~~
test.c:8:5: note: ‘sprintf’ output between 13 and 1031 bytes into a destination
of size 499
8 | sprintf(buf, "%sa = %d\n"
| ^~~~~~~~~~~~~~~~~~~~~~~~~
9 | "%sb = %d\n",
| ~~~~~~~~~~~~~
10 | pfx, a, pfx, b);
| ~~~~~~~~~~~~~~~
test.c:8:5: warning: ‘sprintf’ arguments 3, 5 may overlap destination object
‘buf’ [-Wrestrict]
test.c:17:10: note: destination object referenced by ‘restrict’-qualified
argument 1 was declared here
17 | char buf[500];
| ^~~
It's clear that the destination buffer will NOT overlap with anything related
to "pfx" in the fun() function. Is also clear that output will NOT contain
that many characters that the warning claims (up to 1031). If GCC can't
estimate the length for sure, it's better NOT to emit any warnings, rather than
printing this annoying noise.
Please be mindful of your users -- and their time to re-analyze the code that
suddenly is now flagged with these senseless warnings, only to realize that
it's all red herring.
Thank you
