Buggifying critical core modules [LWN.net]

Buggifying critical core modules

Posted Mar 19, 2008 15:19 UTC (Wed) by tjc (subscriber, #137)
In reply to: Buggifying critical core modules by quotemstr
Parent article: Who maintains dpkg?

> the bit pattern of the pointer is going to be same no matter what --
> provided you pass an actual pointer.

This took me by surprise:

int main(void)
{
        int n;
        void *p = &n;
        printf("%p\n", p);
        p++;
        printf("%p\n", p);

        return 0;
}

I thought incrementing a void pointer would cause a compiler error (or at least a warning),
but it seems to treat it as a char pointer and increment it by one byte on my system (gcc
4.1.2 on Solaris).

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Buggifying critical core modules

Posted Mar 19, 2008 15:26 UTC (Wed) by dw (subscriber, #12017) [Link]

A GCCism:

     -Wpointer-arith
         Warn about anything that depends on the ``size of'' a
         function type or of "void".  GNU C assigns these types a
         size of 1, for convenience in calculations with "void *"
         pointers and pointers to functions.

Buggifying critical core modules

Posted Mar 20, 2008 18:34 UTC (Thu) by dododge (subscriber, #2870) [Link]

The lesson being: when you run "gcc" with no options, it does not compile the C language, but
rather the "GNU C" language.  GNU C bears a strong resemblance to C but has many additional
and alternate semantics.

If you're trying to write portable code and you want gcc to follow Standard C rules, you have
to explicitly request it.  I normally use, at a minimum:

-std=c99 -pedantic -Wall -Wextra