[PATCH] i386-dis: fix decoding of excess prefixes on push segment register

[H.J. Lu]

On Mon, Aug 6, 2012 at 2:01 PM, Roland McGrath <mcgrathr@google.com> wrote:
> objdump produces:
>
>    0:   0f a8                   pushq  %gs
>    2:   41 0f a8                pushq  %bx,%di
>
> The rex.B (0x41) prefix is ignored by the hardware.
>
> The exact failure mode may differ in different builds.  The bogon arises
> from reading off the end of the names_seg[] array, where what happens to
> follow is the index16[] array.
>
> After fixing that, I noticed more bugs in the separate printing of excess
> prefixes and fixed those too.
>
> With these fixes, it produces:
>
>    0:   0f a8                   pushq  %gs
>    2:   41 0f a8                rex.B pushq %gs
>    5:   48 0f a8                rex.W pushq %gs
>    8:   66 48 0f a8             data32 rex.W pushq %gs
>    c:   48                      rex.W
>    d:   41 0f a8                rex.B pushq %gs
>   10:   66 48                   data16 rex.W
>   12:   41 0f a8                rex.B pushq %gs
>
> I don't really understand what determines whether excess prefixes are
> printed as a separate line or before the instruction, and what
> distinguishes data32 from data16.  But at least the distinction between
> what is the actual instruction and what are the unused prefixes is now
> correct.
>
> There are no other 'make check' regressions for x86_64-linux-gnu.
>
> Ok for trunk?
>
>
> Thanks,
> Roland
>
...
> opcodes/
>         * i386-dis.c (print_insn): Print spaces between multiple excess
>         prefixes.

Does your patch contain a testcase for this change?

-- 
H.J.