linux-kernel - Re: [PATCH] perf, x86: Disable sanity check

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Message-ID: <20120419052208.GA29875@somewhere.redhat.com>
Date:	Thu, 19 Apr 2012 07:22:11 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arun Sharma <asharma@...com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Namhyung Kim <namhyung.kim@....com>,
	Tom Zanussi <tzanussi@...il.com>,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf, x86: Disable sanity check

On Wed, Apr 18, 2012 at 04:24:09PM -0700, Arun Sharma wrote:
> Without this patch, applications with two different stack
> regions (eg: native stack vs JIT stack) get truncated 
> callchains even when RBP chaining is present. GDB shows proper
> stack traces and the frame pointer chaining is intact.
> 
> This patch disables the (fp < RSP) check, hoping that other checks
> in the code save the day for us. In our limited testing, this
> didn't seem to break anything.
> 
> In the long term, we could potentially have userspace advise
> the kernel on the range of valid stack addresses, so we don't 
> spend a lot of time unwinding from bogus addresses.

So rbp is part of the JIT stack but not rsp?
Do you have a practical example of that? I must confess I don't know
much about JIT stack.

Thanks.

> 
> Signed-off-by: Arun Sharma <asharma@...com>
> Cc: Ingo Molnar <mingo@...e.hu>
> CC: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Mike Galbraith <efault@....de>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Stephane Eranian <eranian@...gle.com>
> Cc: Namhyung Kim <namhyung.kim@....com>
> Cc: Tom Zanussi <tzanussi@...il.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-perf-users@...r.kernel.org
> 
> ---
>  arch/x86/kernel/cpu/perf_event.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 07f46ba..87d9abd 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -1596,9 +1596,6 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
>  		if (bytes != sizeof(frame))
>  			break;
>  
> -		if ((unsigned long)fp < regs->sp)
> -			break;
> -
>  		perf_callchain_store(entry, frame.return_address);
>  		fp = frame.next_frame;
>  	}
> -- 
> 1.7.8.4
> 
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