linux-kernel - Re: [PATCH] x86-64: Fix CFI data for common

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Date:	Tue, 21 Feb 2012 14:26:05 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Mark Wielaard" <mjw@...hat.com>
Cc:	"Frederic Weisbecker (commit_signer:4/25=16%)" <fweisbec@...il.com>,
	"maintainer:X86 ARCHITECTURE..." <x86@...nel.org>,
	"Thomas Gleixner (maintainer:X86 ARCHITECTURE...)" 
	<tglx@...utronix.de>,
	"Andi Kleen (commit_signer:5/25=20%)" <ak@...ux.intel.com>,
	"commit_signer:11/25=44%) Ingo Molnar (maintainer:X86 ARCHITECTURE..." 
	<mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
	"commit_signer:4/25=16%) H. Peter Anvin (maintainer:X86 ARCHITECTURE..." 
	<hpa@...or.com>
Subject: Re: [PATCH] x86-64: Fix CFI data for common_interrupt

>>> On 21.02.12 at 15:06, Mark Wielaard <mjw@...hat.com> wrote:
> Commit eab9e6 "x86-64: Fix CFI data for interrupt frames" introduced
> a DW_CFA_def_cfa_expression in the SAVE_ARGS_IRQ macro. To later define
> the CFA using a simple register+offset rule both register and offset
> need to be supplied. Just using CFI_DEF_CFA_REGISTER leaves the offset
> undefined. So use CFI_DEF_CFA with reg+off explicitly at the end of
> common_interrupt.

NAK, unless you can prove a path via which the offset will remain
unset until hitting a CFI_DEF_CFA_REGISTER. And if you indeed
found such a path, the entry point of the path is where the problem
ought to be fixed.

Are you perhaps thinking that .cfi_def_cfa_register invalidates
the offset in any way? That, to my knowledge, isn't the case, it
just replaces the CFA register with the one specified, leaving the
offset unchanged.

Jan

> Signed-off-by: Mark Wielaard <mjw@...hat.com>
> ---
>  arch/x86/kernel/entry_64.S |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 3fe8239..e00ef55 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -813,7 +813,7 @@ ret_from_intr:
>  
>  	/* Restore saved previous stack */
>  	popq %rsi
> -	CFI_DEF_CFA_REGISTER	rsi
> +	CFI_DEF_CFA rsi,0	/* needed after def_cfa_expression */
>  	leaq ARGOFFSET-RBP(%rsi), %rsp
>  	CFI_DEF_CFA_REGISTER	rsp
>  	CFI_ADJUST_CFA_OFFSET	RBP-ARGOFFSET
> -- 
> 1.7.7.6



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