linux-kernel - Re: [PATCH 3/4] x86/insn: Extract more information about instructions

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Message-ID: <53509EB9.5070001@hitachi.com>
Date:	Fri, 18 Apr 2014 12:40:41 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, vegard.nossum@...cle.com,
	penberg@...nel.org, jamie.iles@...cle.com, mingo@...hat.com,
	tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] x86/insn: Extract more information about instructions

(2014/04/18 2:31), Sasha Levin wrote:
>> I also have seen several attempts at using the generic instruction
>> decoder which has resulted in more complexity, not less, because of
>> excess generality, so it is not an obvious thing.
> 
> Let's split this patchset into two:
> 
> We have one part which moves kmemcheck to the generic instruction decoder
> and adds memory access size to the instruction decoder. There seems to be
> no objection to that part beyond technical issues regarding how we store
> the new size value.

This looks OK to me.

> The other part is adding mnemonics to the instruction decoder. If my
> explanation above makes sense, and kmemcheck does need to know about AND,
> OR, XOR, MOVS and CMPS then let me know how to proceed about changing
> the instruction decoder to add that functionality.

I don't think we need to add such things to instruction decoder.
You'd better start from clarifying the bit pattern of those instructions
and making macros or inlines which evaluate insn->opcode.value.

Using automatic generated macros for immediate in the source code always
leads misunderstanding and abuse, and is hard to fix if a bug is there.
I strongly recommend you to define instruction classification macros
for their use by hand. That's easy to review too.
Actually x86 has a long history and its mnemonics are not so simple...

Thank you,

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


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