Re: [PATCH 5/6] x86: Remove useless unwinder backlink from irq regs saving

From: Jan Beulich
Date: Mon Jul 04 2011 - 03:29:16 EST


>>> On 02.07.11 at 18:29, Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:
> The unwinder backlink in interrupt entry is very useless.
> It's actually not part of the stack frame chain and thus is
> never used.

I very much doubt this - see dump_trace()'s comment in its IRQ-stack
related code portion (and the corresponding use of irq_stack_end[-1]).

Jan

> Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Jan Beulich <JBeulich@xxxxxxxxxx>
> ---
> arch/x86/kernel/entry_64.S | 1 -
> 1 files changed, 0 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 20dc8e6..6131432 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -327,7 +327,6 @@ ENDPROC(native_usergs_sysret64)
> jne 2f
> mov PER_CPU_VAR(irq_stack_ptr),%rsp
> EMPTY_FRAME 0
> - pushq_cfi %rbp /* backlink for unwinder */
> /*
> * We entered an interrupt context - irqs are off:
> */




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