[Xcb] Alignment problems in XKB GetGeometry

[Ran Benita]

On Tue, Aug 06, 2013 at 12:24:50AM +0200, Daniel Martin wrote:
> On Mon, Aug 05, 2013 at 10:45:09AM +0300, Ran Benita wrote:
> > On Mon, Aug 05, 2013 at 01:21:10AM +0200, Daniel Martin wrote:
> > > On Sun, Aug 04, 2013 at 11:57:10PM +0300, Ran Benita wrote:
> > So something's wrong here.
> 
> It's XCB_TYPE_PAD(). In this case (sizeof(xcb_xkb_property_t)==0) it
> negates prev.index. I've attached a patch which changes XCB_TYPE_PAD to
> return 0 here. At least it makes your test programm (having Property
> with 2 CountedString16) to run without raising an assertion.
> 
> I didn't made it a real git patch. Because, I think we've to add an
> XCB_ALIGN_PAD(), which would align based upon prev.data + prev.index and
> change the generated code to check the size of the type and use either
> XCB_TYPE_PAD or XCB_ALIGN_PAD. But, I'm not sure atm. if that's the
> correct solution. (Could be that prev.data + prev.index is already
> aligned.)
>
> diff --git a/src/xcb.h b/src/xcb.h
> index f7dc6af..45796f1 100644
> --- a/src/xcb.h
> +++ b/src/xcb.h
> @@ -87,7 +87,7 @@ extern "C" {
>  /** Connection closed because the server does not have a screen matching the display. */
>  #define XCB_CONN_CLOSED_INVALID_SCREEN 6
>  
> -#define XCB_TYPE_PAD(T,I) (-(I) & (sizeof(T) > 4 ? 3 : sizeof(T) - 1))
> +#define XCB_TYPE_PAD(T,I) (sizeof(T) > 0 ? -(I) & (sizeof(T) > 4 ? 3 : sizeof(T) - 1) : 0)
>  
>  /* Opaque structures */
>  

Thanks, with this patch I was able to test the other parts. Attached is
an updated test. The parts which rely on the xcb_xkb_doodad_t union size
TODO are commented out,

I'm afraid I still don't know enough about the code generator to offer a
proper solution myself either. We need some other solution then the
empty struct though; it causes this compiler warning:

    xkb.h:878:16: warning: struct has no members [-Wpedantic]
        typedef struct xcb_xkb_property_t {
        }

And we probably can't rely on its sizeof() being 0. I'll try to figure
out why the other fix I tried didn't work.

Ran
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