Re: Re: Re: [RFC PATCH 4/6] uprobes/x86: Emulate rip-relative call's

[Masami Hiramatsu]

(2014/04/11 21:23), Denys Vlasenko wrote:
> On Fri, Apr 11, 2014 at 5:03 AM, Masami Hiramatsu
> <masami.hiramatsu.pt@xxxxxxxxxxx> wrote:
>> At least, if we can trust Intel SDM, it says that depends
>> on the operand-size (insn->opnd_bytes) and stack segment
>> descriptor. Please check the SDM vol.1 6.2.2 Stack Alignment
>> and vol.2a, 3.2 Instructions (A-M), CALL--Call Procedure.
>> But we'd better check it on x86-32.
> 
> I am past trusting CPU manuals on this one:
> 
> By now I verified on the real hardware that AMD and Intel CPUs
> handle this insn differently in 64-bit mode: Intel ignores 0x66 prefix.
> AMD treats this insn the same as in 32-bit mode: as 16-bit insn.
> 
> (Should I submit a patch adding comment about it
> in x86-opcode-map.txt?)

Yeah, feel free to do so :)

> So there is no universally "correct" way to emulate it.
> 
> We, theoretically, can decode it differently *depending
> on actual CPU(s) on the system*... do we really want
> to go *that* far? I guess not.

No I guess not too. If we start such thing, we need to cover
other x86 variants too... And actually jump/callw is not a
normal instructions.

BTW, I can see that difference on AMD64 architecture programmers
manual vol.3 appendix A. It seems that the difference is by
design...

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx


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