[dns-operations] dnscap -s

[Anand Buddhdev]

On Jul 22, 2007, at 7:29, Paul Vixie wrote:

>> dnscap.c: In function 'dl_pkt':
>> dnscap.c:964: warning: cast discards qualifiers from pointer  
>> target type
>> make: *** [dnscap.o] Error 1
>
> in your /usr/include/arpa/nameser.h, does your NS_GET32 macro look  
> like this?
>
> #define NS_GET32(l, cp) do { \
>         register const u_char *t_cp = (const u_char *)(cp); \
>         (l) = ((u_int32_t)t_cp[0] << 24) \
>             | ((u_int32_t)t_cp[1] << 16) \
>             | ((u_int32_t)t_cp[2] << 8) \
>             | ((u_int32_t)t_cp[3]) \
>             ; \
>         (cp) += NS_INT32SZ; \
> } while (0)

On both CentOS 4.4 (glibc 2.3.4), and Ubuntu 7.04 (glibc 2.5), this  
macro looks like this:

#define NS_GET32(l, cp) do { \
         register u_char *t_cp = (u_char *)(cp); \
         (l) = ((u_int32_t)t_cp[0] << 24) \
             | ((u_int32_t)t_cp[1] << 16) \
             | ((u_int32_t)t_cp[2] << 8) \
             | ((u_int32_t)t_cp[3]) \
             ; \
         (cp) += NS_INT32SZ; \
} while (0)


> dnscap.c:964 is "NS_GET32(x, pkt);" where "x" is declared as  
> "uint32_t" and
> "pkt" is declared as "const u_char *".  the only "qualifier" this  
> error msg
> could refer to use "const", and this qualifier is present on every  
> cast except
> the four (u_int32_t)'s on t_cp, where it's clearly binding to the  
> array deref
> or else the array deref would be to a u_int32_t.
>
> so there's something terribly gutshot in your /usr/include/arpa/ 
> nameser.h file
> and i'd love to see what centos 4.4 has come up with that breaks  
> this otherwise
> portable code which tries to use an otherwise portable, and common,  
> interface.
>
> if i'm misreading the error, misunderstanding GCC's intent, or  
> being stupid
> about C, i trust that several folks here will step forward to  
> educate me?

I don't quite understand what you are trying to explain here, but I  
hope that what I've pasted above helps you understand the source of  
the error message.

Regards,

-- 
Anand