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

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Date:	Tue, 16 Apr 2013 03:05:25 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Oleg Nesterov <oleg@...hat.com>,
	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 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?

[...]
> --- a/arch/x86/include/asm/sighandling.h
> +++ b/arch/x86/include/asm/sighandling.h
> @@ -7,10 +7,10 @@
>  
>  #include <asm/processor-flags.h>
>  
> -#define __FIX_EFLAGS	(X86_EFLAGS_AC | X86_EFLAGS_OF | \
> +#define FIX_EFLAGS	(X86_EFLAGS_AC | X86_EFLAGS_OF | \
>  			 X86_EFLAGS_DF | X86_EFLAGS_TF | X86_EFLAGS_SF | \
>  			 X86_EFLAGS_ZF | X86_EFLAGS_AF | X86_EFLAGS_PF | \
> -			 X86_EFLAGS_CF)
> +			 X86_EFLAGS_CF | X86_EFLAGS_RF)
>  
>  void signal_fault(struct pt_regs *regs, void __user *frame, char *where);
>  
> diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
> index 6956299..9df4c0b 100644
> --- a/arch/x86/kernel/signal.c
> +++ b/arch/x86/kernel/signal.c
> @@ -43,12 +43,6 @@
>  
>  #include <asm/sigframe.h>
>  
> -#ifdef CONFIG_X86_32
> -# define FIX_EFLAGS	(__FIX_EFLAGS | X86_EFLAGS_RF)
> -#else
> -# define FIX_EFLAGS	__FIX_EFLAGS
> -#endif

So, I'm a bit confused here. Why was that only hapenning in X86_64?

> -
>  #define COPY(x)			do {			\
>  	get_user_ex(regs->x, &sc->x);			\
>  } while (0)
> -- 
> 1.7.11.7
> 
--
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