linux-kernel - Re: [PATCH 1/6] signal x86: Propage RF EFLAGS bit throught the signal restore call

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Date:	Wed, 24 Apr 2013 17:39:15 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/6] signal x86: Propage RF EFLAGS bit throught the
 signal restore call

On Wed, Apr 17, 2013 at 10:02:06PM +0200, Oleg Nesterov wrote:
> On 04/16, Oleg Nesterov wrote:
> >
> > On 04/16, Frederic Weisbecker wrote:
> > >
> > > On Sun, Mar 10, 2013 at 07:41:06PM +0100, Jiri Olsa wrote:
> > > > Adding RF EFLAGS bit to be restored on return from signal from
> > > > the original register context before the signal was entered.
> > > >
> > > > This will prevent the RF flag to disappear when returning
> > > > from exception due to the signal handler being executed.
> > >
> > > So that happens if, say, we get a breakpoint exception and then we
> > > run a signal handler before returning to the ip that triggered the
> > > breakpoint?
> >
> > Afaics these changes (1 and 2) should fix the bug.
> >
> > Suppose that the first insn in the signal handler should trigger
> > another bp, we should clear X86_EFLAGS_RF (2/6).
> >
> > Otoh, we should restore it when we return to the original insn
> > which triggered the trap to avoid another trap.
> 
> I applied 1 and 2, and this fixes the test-case below.
> 
> > But. it seems that we have yet another problem? Suppose that
> > the signal handler does siglongjmp() and jumps to yet another
> > insn which should trigger the trap?
> 
> Argh. Sorry for confusion. I tried to say that the signal handler
> can play with sigcontext->ip before sigreturn(). But probably we
> can ignore this.

Hmm, ok.

Anyway patches 1-3 look good!

Thanks!
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