Re: [PATCH] perf, x86: Disable sanity check

[Frederic Weisbecker]

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@xxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> CC: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: Mike Galbraith <efault@xxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Cc: Namhyung Kim <namhyung.kim@xxxxxxx>
> Cc: Tom Zanussi <tzanussi@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-perf-users@xxxxxxxxxxxxxxx
> 
> ---
>  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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