linux-kernel - Re: [PATCH 12/X] uprobes: x86: introduce abort

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Message-ID: <20111022070952.GA24475@in.ibm.com>
Date:	Sat, 22 Oct 2011 12:39:52 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 12/X] uprobes: x86: introduce abort_xol()

On Fri, Oct 21, 2011 at 06:42:21PM +0200, Oleg Nesterov wrote:
> On 10/21, Ananth N Mavinakayanahalli wrote:

...

> > For instance, on x86, it points to the next
> > instruction,
> 
> No?

At exception entry, we'd not have done the following fixup...

> 	/**
> 	 * get_uprobe_bkpt_addr - compute address of bkpt given post-bkpt regs
> 	 * @regs: Reflects the saved state of the task after it has hit a breakpoint
> 	 * instruction.
> 	 * Return the address of the breakpoint instruction.
> 	 */
> 	unsigned long __weak get_uprobe_bkpt_addr(struct pt_regs *regs)
> 	{
> 		return instruction_pointer(regs) - UPROBES_BKPT_INSN_SIZE;
> 	}
> 
> Yes, initially regs->ip points to the next insn after int3, but
> utask->vaddr == get_uprobe_bkpt_addr() == addr of int3.
> 
> Right?

Yes, we fix it up so we point to the right (breakpoint) address.

> > while on powerpc, the nip points to the breakpoint vaddr
> > at the time of exception.
> 
> I think get_uprobe_bkpt_addr() should be consistent on every arch.
> That is why (I think) it is __weak.

Yes, that is the intention.

> Anyway, abort_xol() has to be arch-specific.

Agree.

Ananth
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