[Bug c/39044] -Wformat warns on printf() with stringpointer as sole argument

[Bug c/39044] -Wformat warns on printf() with stringpointer as sole argument

[p4bgtech at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39044

p4bgtech at gmail dot com changed:

           What    |Removed                     |Added
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                 CC|                            |p4bgtech at gmail dot com

--- Comment #4 from p4bgtech at gmail dot com 2011-03-18 06:35:11 UTC ---
No warning displayed on gcc-4.5.1..

[Bug c/39044] -Wformat warns on printf() with stringpointer as sole argument

[bugdal at aerifal dot cx]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39044

Rich Felker <bugdal at aerifal dot cx> changed:

           What    |Removed                     |Added
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                 CC|                            |bugdal at aerifal dot cx

--- Comment #5 from Rich Felker <bugdal at aerifal dot cx> 2012-05-06 04:23:14 UTC ---
This warning is valid and highly desirable. Any call to printf with a single
non-string-literal argument is almost surely an extremely serious security bug.
And there's rarely a legitimate reason to make such a call; the closest thing
to a legitimate use I can think of would be lazy/sloppy use of gettext. If the
string is not a format string, you should use fputs or fwrite to print it.

[Bug c/39044] -Wformat warns on printf() with stringpointer as sole argument

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39044

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |manu at gcc dot gnu.org
         Resolution|                            |WONTFIX

--- Comment #6 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-05-06 12:26:36 UTC ---
(In reply to comment #2)
> Ah, you're right. Gentoo enables -Wformat-security by default now. I'll bug
> them about this.
> 
> On the other hand, this does not generate a warning. Why?

printf(s) is always wrong. You should have used fputs().

To get a warning for printf(s,t), you need -Wformat=2 (or -Wformat-nonliteral).
I guess the reason is that there is no real alternative if you need such a
code.

(In reply to comment #3)
> i'd reconstruct this report as gcc not properly handling constant strings with
> printf() when the string is readily available to it and clearly does not change

In the examples here, the code is arguably safe, and GCC should not warn. But
to reach that conclusion, the front ends would need to do constant propagation,
and this is not implemented, and not likely to be ever implemented by existing
contributors. I think it would be widely useful to have some sort of constant
propagation in the FEs, but it would take someone extremely motivated and
skilled to get it done properly. Unfortunately, I am not aware of any
candidates. If you know of any, please let me know.

[Bug c/39044] -Wformat warns on printf() with stringpointer as sole argument

[vapier at gentoo dot org]

------- Comment #3 from vapier at gentoo dot org  2009-02-25 23:58 -------
i'd reconstruct this report as gcc not properly handling constant strings with
printf() when the string is readily available to it and clearly does not change

as for the kernel and this warning flag, that's a different issue


-- 

vapier at gentoo dot org changed:

           What    |Removed                     |Added
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                 CC|                            |toolchain at gentoo dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39044

[Bug c/39044] -Wformat warns on printf() with stringpointer as sole argument

[mano at roarinelk dot homelinux dot net]

------- Comment #2 from mano at roarinelk dot homelinux dot net  2009-01-31 06:14 -------
(In reply to comment #1)
> GNU C (GCC) version 4.3.3 20081218 (prerelease) [gcc-4_3-branch revision
> 142804] (i386-apple-darwin8.11.1)
> 
> 
> Did you modify GCC at all?

Ah, you're right. Gentoo enables -Wformat-security by default now. I'll bug
them about this.

On the other hand, this does not generate a warning. Why?

---- 8< ------- 8< --------
#include <stdio.h>
int main()
{
  static const char *s = "hello", *t = " world";

  printf(s, t);
  return 0;
}

----- 8< ------ 8< ---------


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39044

[Bug c/39044] -Wformat warns on printf() with stringpointer as sole argument

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2009-01-31 01:10 -------
[dhcp-10-98-10-23:~] apinski% ~/gcc4.3-gcc/bin/gcc -Wformat t.c -W -Wall
[dhcp-10-98-10-23:~] apinski% ~/gcc4.3-gcc/bin/gcc -Wformat t.c -W -Wall
-Wformat-security
t.c: In function 'main':
t.c:5: warning: format not a string literal and no format arguments

GNU C (GCC) version 4.3.3 20081218 (prerelease) [gcc-4_3-branch revision
142804] (i386-apple-darwin8.11.1)


Did you modify GCC at all?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39044