linux-kernel - Re: [RFC PATCH 0/6] uprobes/x86: fix the reprel jmp/call handling

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Message-ID: <1396896852.9333.14.camel@oc7886638347.ibm.com.usor.ibm.com>
Date:	Mon, 07 Apr 2014 11:54:12 -0700
From:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <aarapov@...hat.com>,
	David Long <dave.long@...aro.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jonathan Lebon <jlebon@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/6] uprobes/x86: fix the reprel jmp/call handling

On Sun, 2014-04-06 at 22:15 +0200, Oleg Nesterov wrote:
> On 04/04, Jim Keniston wrote:
> >
> > On Fri, 2014-04-04 at 21:32 +0200, Oleg Nesterov wrote:
> > >
> > > 	1. Why insn_get_displacement() doesn't work? See "HELP!!!"
> > > 	   below.
> >
> > insn->moffset1.value seems to be what you want.
> 
> Works! Thanks a lot.
> 
> Still I can't understand why displacement.nbytes == 0 in this case...
> Nevermind.

Looking at Masami's arch/x86/lib/x86-opcode-map.txt and related code, I
see that the operands to the Jcc and JMP instructions are treated as
immediate values.  So insn->immediate.value (which is in the same union
as insn->moffset1.value) is more appropriate, and insn->immediate.nbytes
should get you the correct size.  Again, insn_get_length() finishes
parsing the whole instruction as necessary, so insn_get_immediate() gets
called as a side effect.

> 
> OK. Please see the RFC changes. Obviously not for inclusion yet. And
> totally untested, except I verified that the test-case from 4/6 works.
> 
> Please comment.

I'll look at the new patches today.

> 
> Oleg.

Jim

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