[Xcb] xcb-proto commit f91186b9f3 (dri2 padding) breaks build

[Vincent Torri]

On Mon, 17 May 2010, Alan Coopersmith wrote:

> I cannot build libxcb when commit f91186b9f3e55e1d478476749c929b86e2865cc8
> is present, but going back to the previous commit allows it to build fine.
>
> With that commit in place, building gives the error:
>
> "dri2.c", line 332: cannot take sizeof void
>
> The code from the generated dri2.c here is:
>
>    328 void *
>    329 xcb_dri2_connect_alignment_pad (const xcb_dri2_connect_reply_t *R  /**< */)
>    330 {
>    331     xcb_generic_iterator_t prev = xcb_dri2_connect_driver_name_end(R);
>    332     return (void *) ((char *) prev.data + XCB_TYPE_PAD(void, prev.index)
> + 0);
>    333 }
>
> After cpp expansion the last line has become:
>
> return (void *) ((char *) prev.data +  ( - ( prev . index ) & ( sizeof ( void )
>> 4 ? 3 : sizeof ( void ) - 1 ) ) + 0);
>
> and like the compiler, I have no idea what size a "void" is.
>
> Is something wrong in the code generator that's generating different code here
> for me, or does gcc allow taking the size of sizeless types like void?

it's a gcc extension: sizeof(void) == 1 and arithmetic on void pointers is 
like on unsigned char pointers. suncc does not support that (and i hope 
that it will never support such weirdness).

See:

http://gcc.gnu.org/onlinedocs/gcc-4.4.2/gcc/Pointer-Arith.html#Pointer-Arith

Alan: fwiw, I've already asked that in the tools-compilers ML (subject : 
'about the warning "pointer to void or function used in arithmetic"')

regards

Vincent

>
> (I'm building on OpenSolaris with the Sun compilers.)
>
> --
> 	-Alan Coopersmith-        alan.coopersmith at oracle.com
> 	 Oracle Solaris Platform Engineering: X Window System
>
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