linux-kernel - Re: [PATCH 3/7] uprobes/x86: Conditionalize the usage of handle_riprel

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Date:	Tue, 1 Apr 2014 16:33:46 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	David Long <dave.long@...aro.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Jonathan Lebon <jlebon@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] uprobes/x86: Conditionalize the usage of
	handle_riprel_insn()

On 04/01, Masami Hiramatsu wrote:
>
> (2014/04/01 4:44), Oleg Nesterov wrote:
> > arch_uprobe_analyze_insn() calls handle_riprel_insn() at the start,
> > but only "0xff" and "default" cases need the UPROBE_FIX_RIP_ logic.
> > Move the callsite into "default" case and change the "0xff" case to
> > fall-through.
> >
> > We are going to add the various hooks to handle the rip-relative
> > jmp/call instructions (and more), we need this change to enforce the
> > fact that the new code can't conflict with is_riprel_insn() code.
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
>
> Hmm, this seems not obviously reasonable at this point.
> However, the code itself is not wrong. Could you merge
> this change to that new hooks?

Good point, I'll send v2.

I'd still prefer to do this in a separate patch if you do not object,
and this patch should come after "add uprobe_xol_ops". In this case
it should be more clear why do we need this change, and the changelog
can tell more. Say, it can mention that otherwise uprobe_abort_xol()
can be confused until at least we add uprobe_xol_ops->abort().

And probably I'll add another patch into this series, "restart if
->post_xol() fails" (see "TODO:" in 7/7). We need this change anyway
to emulate the "call" insn. We could fix this before we add the hooks,
but after 7/7 the change will be more simple/clear.

Thanks!

Oleg.

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