Bug#657215: x11proto-video-dev: sizeof(xvEncodingInfo) vs sz_xvEncodingInfo
Package: x11proto-video-dev
Version: 2.3.1-2
Severity: normal
File: /usr/include/X11/extensions/Xvproto.h
The program foo.c below with gcc 4.6.1-3 prints
sizeof(xvEncodingInfo) 24
sz_xvEncodingInfo 20
where if I'm not mistaken the two are supposed to be equal.
It looks like in the xvEncodingInfo the xvRational field is padded onto
a 4-byte boundary so
CARD32 encoding
CARD16 name_size
CARD16 width
CARD16 height
<compiler padding 16>
INT32 rate.num
INT32 rate.den
CARD16 pad
<compiler padding 16>
= 24 bytes
Perhaps since the rate is 2*INT32 the pad was always supposed to be
before, as
typedef struct {
XvEncodingID encoding B32;
CARD16 name_size B16;
CARD16 width B16, height B16;
CARD16 pad B16;
xvRational rate;
} xvEncodingInfo;
The server circa 1.7.7 seems to spit out 20 bytes in that form. If I'm
not mistaken it uses sz_xvEncodingInfo rather than sizeof, so quietly
ignores the "pad" field at the end. Eg. reply from QueryEncodings
0000000: 01d9 0600 0700 0000 0100 d7bf 8243 0708 .............C..
0000010: 0000 0000 e63f 0d01 0000 0000 e43f 0d01 .....?.......?..
0000020: 0000 0000 0800 fe07 fe07 0d01 0100 0000 ................
0000030: 0100 0000 5856 5f49 4d41 4745 ....XV_IMAGE
The xlib XvQueryEncodings() looks like it uses sz_xvEncodingInfo too,
but I don't have anything with more than one encoding to try to provoke
it.
Presuming what the server sends is correct (or at least is much too late
to change now :-) then perhaps it'd be worth moving the "pad" field to
where it is actually in effect, making the struct size match what's
sent.
Dunno if that would have to rate as a break of binary compatibility.
Presumably yes strictly speaking if anyone exposed that struct in their
interface, but in practice I expect no if it's only ever meant as a
temporary to layout data on send or receive.
#include <stdio.h>
#include <X11/extensions/Xvproto.h>
int
main (void)
{
printf ("sizeof(xvEncodingInfo) %u\n", sizeof(xvEncodingInfo));
printf ("sz_xvEncodingInfo %u\n", sz_xvEncodingInfo);
return 0;
}
-- System Information:
Debian Release: wheezy/sid
APT prefers unstable
APT policy: (990, 'unstable')
Architecture: i386 (i686)
Kernel: Linux 2.6.32-5-486
Locale: LANG=en_AU, LC_CTYPE=en_AU (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/dash
-- no debconf information
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