Bug#318218: Thoughts :-)

[Nathanael Nerode <neroden@twcny.rr.com>]

This can probably be fixed by changing the following stanza from
xc/programs/Xserver/hw/xfree86/common/compiler.h:

# else /* !__alpha__ && !__powerpc__ && !__sparc__ */

#  define MMIO_IN8(base, offset) \
        *(volatile CARD8 *)(((CARD8*)(base)) + (offset))
#  define MMIO_IN16(base, offset) \
        *(volatile CARD16 *)(void *)(((CARD8*)(base)) + (offset))
#  define MMIO_IN32(base, offset) \
        *(volatile CARD32 *)(void *)(((CARD8*)(base)) + (offset))
#  define MMIO_OUT8(base, offset, val) \
        *(volatile CARD8 *)(((CARD8*)(base)) + (offset)) = (val)
#  define MMIO_OUT16(base, offset, val) \
        *(volatile CARD16 *)(void *)(((CARD8*)(base)) + (offset)) = (val)
#  define MMIO_OUT32(base, offset, val) \
        *(volatile CARD32 *)(void *)(((CARD8*)(base)) + (offset)) = (val)

OK.  The problem with this is that the cast to volatile CARD8* (et al) doesn't 
create a volatile object from the point of view of GCC4.  (GCC4 may be wrong 
here.)  However, code like the following, if I'm not mistaken, *does* create 
a volatile object, and GCC4 notices:

static inline unsigned char
xorgReadMmio8(volatile void * base, const unsigned long offset)
{
  volatile CARD8 * tmp;
  tmp = (CARD8*)base + offset;
  return *tmp;
}
#define MMIO_IN8(base, offset) xorgReadMmio8(base, offset)

(Based on a little testing of simplified code, GCC is smart enough to optimize 
away nearly everything in this, leaving nicely optimized assembly which still
does the memory read, even when the resulting data is never accessed.)

So a consistent replacement along these lines should do the trick.
Shall I whip up a patch?