linux-kernel - Re: [PATCH 1/2] x86: make save_stack_address() !CONFIG_FRAME

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Date:	Thu, 03 Jun 2010 12:53:52 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86: make save_stack_address() !CONFIG_FRAME_POINTER
 friendly

On 6/3/2010 12:32 PM, Oleg Nesterov wrote:
> If CONFIG_FRAME_POINTER=n, print_context_stack() shouldn't neglect the
> non-reliable addresses on stack, this is all we have if dump_trace(bp)
> is called with the wrong or zero bp.
>
> For example, /proc/pid/stack doesn't work if CONFIG_FRAME_POINTER=n.
>
> This patch obviously has no effect if CONFIG_FRAME_POINTER=y, otherwise
> it reverts 1650743c "x86: don't save unreliable stack trace entries".
>    

would be nice if there was a compile time thing to detect if frame 
pointers are on ratehr than an ifdef.

you're now also changing the rules; until now, you would ALWAYS get a 
backtrace without noise....
now that's changing quite a bit. How are various tools (like perf and 
sysprof) going to cope with that?

> Also, remove the unnecessary type-cast.
>
> Signed-off-by: Oleg Nesterov<oleg@...hat.com>
> ---
>
>   arch/x86/kernel/stacktrace.c |    6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> --- 34-rc1/arch/x86/kernel/stacktrace.c~SAVE_STACK_WO_FP	2010-06-03 18:43:27.000000000 +0200
> +++ 34-rc1/arch/x86/kernel/stacktrace.c	2010-06-03 21:29:52.000000000 +0200
> @@ -26,8 +26,10 @@ static int save_stack_stack(void *data,
>   static void save_stack_address(void *data, unsigned long addr, int reliable)
>   {
>   	struct stack_trace *trace = data;
> +#ifdef CONFIG_FRAME_POINTER
>   	if (!reliable)
>   		return;
> +#endif
>   	if (trace->skip>  0) {
>   		trace->skip--;
>   		return;
> @@ -39,9 +41,11 @@ static void save_stack_address(void *dat
>   static void
>   save_stack_address_nosched(void *data, unsigned long addr, int reliable)
>   {
> -	struct stack_trace *trace = (struct stack_trace *)data;
> +	struct stack_trace *trace = data;
> +#ifdef CONFIG_FRAME_POINTER
>   	if (!reliable)
>   		return;
> +#endif
>   	if (in_sched_functions(addr))
>   		return;
>   	if (trace->skip>  0) {
>
>    

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