Re: [Xen-devel] [PATCH] x86emul: defer rIP-relative address calculation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.12.16 at 16:43, <JBeulich@xxxxxxxx> wrote:
>>>> On 07.12.16 at 16:38, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 07/12/16 14:07, Jan Beulich wrote:
>>> By putting it after all instruction fetching has been done, we can both
>>> simplify the existing handling of immediate operands and take care of
>>> any future instructions allowing rIP-relative operands and getting
>>> additional bytes fetched in x86_decode_*() (the current cases of extra
>>> bytes getting fetched there are only for operands without ModR/M bytes,
>>> or with them only allowing their register forms).
>>>
>>> Similarly the new placement of truncate_ea() will take care of any
>>> future cases of non-standard memory operands (the one existing case -
>>> opcodes A0...A3 - are fine with and without this, as they fetch an
>>> ad_bytes sized unsigned address anyway).
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> 
>> This is rather clearer to follow.
>> 
>> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, although...
>> 
>>>
>>> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
>>> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
>>> @@ -1925,6 +1925,7 @@ x86_decode(
>>>      uint8_t b, d, sib, sib_index, sib_base;
>>>      unsigned int def_op_bytes, def_ad_bytes, opcode;
>>>      enum x86_segment override_seg = x86_seg_none;
>>> +    bool ip_rel = false;
>> 
>> I would name this specifically rip_rel, as that is the term used in all
>> the manuals.
> 
> And I specifically avoided it as being wrong in the context of the
> 32-bit test harness. Would pc_rel suit you better than ip_rel?

Actually the reference to the 32-bit test harness was wrong here
(obviously). Instead, it is wrong in the context of 32-bit addressing
in 64-bit mode.

Jan


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