Bug#657215: [PATCH videoproto] Xvproto: fix xvEncodingInfo to match actual wire protocol

[Alan Coopersmith <alan.coopersmith@oracle.com>]

On 06/ 9/13 10:00 AM, Julien Cristau wrote:
> The padding is *before* the rate field, so the rate is placed on a 32bit
> boundary.  This change adds explicit padding between height and rate,
> and removes extraneous padding after the rate field, which the server
> never sent and xlib never read.
>
> This changes sizeof(xvEncodingInfo).  Hopefully that's not a big deal as
> clients only see the Xlib structure XvEncodingInfo.
>
> Debian bug#657215
>
> Reported-by: Kevin Ryde <user42@zip.com.au>
> Signed-off-by: Julien Cristau <jcristau@debian.org>

This looked reasonable to me, but just to be sure, I threw together the
attached test program and confirmed it doesn't change where in the
struct the rate data appears, due to the compiler silently inserting
padding to reach 32-bit alignment.

In both 32-bit & 64-bit, on both SPARC & x86, all 4 returned:

                 OLD  NEW
offsetof(rate):   12  12
offsetof(pad):    20  10
sizeof(struct):   24  20

which matches my expectations, so:

Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>

--
	-Alan Coopersmith-              alan.coopersmith@oracle.com
	 Oracle Solaris Engineering - http://blogs.oracle.com/alanc

#include <stdio.h>
#include <stddef.h>
#include <X11/Xmd.h>

#define XvEncodingID CARD32

typedef struct {
  INT32 numerator B32;
  INT32 denominator B32;
} xvRational;

typedef struct {
  XvEncodingID encoding B32;
  CARD16 name_size B16;
  CARD16 width B16, height B16;
  xvRational rate;
  CARD16 pad B16;
} OLDxvEncodingInfo;

typedef struct {
  XvEncodingID encoding B32;
  CARD16 name_size B16;
  CARD16 width B16, height B16;
  CARD16 pad B16;
  xvRational rate;
} NEWxvEncodingInfo;

int main(int argc, char **argv)
{
    printf("                 OLD  NEW\n");
    printf("offsetof(rate):   %2d  %2d\n",
           offsetof(OLDxvEncodingInfo, rate),
           offsetof(NEWxvEncodingInfo, rate));
    printf("offsetof(pad):    %2d  %2d\n",
           offsetof(OLDxvEncodingInfo, pad),
           offsetof(NEWxvEncodingInfo, pad));
    printf("sizeof(struct):   %2d  %2d\n",
           sizeof(OLDxvEncodingInfo),
           sizeof(NEWxvEncodingInfo));
}