Bug#247436: libc6-dev: odd dev_t/varargs behavior

[Herbert Xu <herbert@gondor.apana.org.au>]

Andres Salomon <dilinger@voxel.net> wrote:
> Package: libc6-dev
> Version: 2.3.2.ds1-12
> Severity: normal
> 
> I'm seeing some very odd behavior with dev_t (defined in linux/kdev_t.h)
> and varargs.  I have the following source file:
> 
> #include <stdio.h>
> #include <sys/types.h>
> #include <linux/kdev_t.h>
>                                                                                
> int main(void)
> {
>        dev_t x = 0x3af;
>        printf("%x %x\n", ((x)>>8), ((x)&0xff));
>        return 0;
> }
> 
> 
> One would think that this would print out "3 af"; however, it displays
> "3 0".  If I change that printf to:
>        printf("%x %x %x\n", ((x)>>8), ((x)&0xff));

Please review the C promotion rules.

The 2nd and 3rd arguments are 64-bits long, and therefore they get pushed
onto the stack as 64-bit values.  Your use of the %x conversion is
therefore incorrect.

In fact, gcc -Wall should've told you about it.
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