On 07/01/2016 08:15 PM, Martin Sebor wrote:
The attached patch enhances compile-time checking for buffer overflow
and output truncation in non-trivial calls to the sprintf family of
functions under a new option -Wformat-length=[12]. This initial
patch handles printf directives with string, integer, and simple
floating arguments but eventually I'd like to extend it all other
functions and directives for which it makes sense.
I tried your patch with the following code, which is close to a
real-world example:
#include <stdio.h>
void print (const char *);
void
format_1 (unsigned address)
{
unsigned char a = address >> 24;
unsigned char b = address >> 16;
unsigned char c = address >> 8;
unsigned char d = address;
char buf[15];
sprintf ("%u.%u.%u.%u", buf, a, b, c, d);
print (buf);
}
void
format_2 (unsigned address)
{
char buf[15];
sprintf ("%u.%u.%u.%u", buf,
address >> 24,
(address >> 16) & 0xff,
(address >> 8) & 0xff,
address & 0xff);
print (buf);
}
I didn't get a warning (with -O2 and -Wformat-length=1 or
-Wformat-length=2). If the warning is implemented in builtin folding, I
guess this has to be expected because there is no range information, and
warning for all %us similar to those in the example would produce too
many false positives.
Florian
