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Date: Thu, 26 Nov 2015 08:43:35 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Jiri Olsa <jolsa@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, David Ahern <dsahern@gmail.com>,
        Kan Liang <kan.liang@intel.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Andi Kleen <andi@firstfloor.org>, Wang Nan <wangnan0@huawei.com>
Subject: Re: [PATCH 2/3] perf callchain: Stop resolving callchains after
 invalid address
Message-ID: <20151126074335.GA18742@gmail.com>
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* Namhyung Kim <namhyung@kernel.org> wrote:

> Unwinding optimized binaries using frame pointer gives garbage.  Check
> callchain address and stop if it's under vm.mmap_min_addr sysctl value.
> 
> Before:
>   $ perf report --stdio --no-children -g callee
>   ...
> 
>    1.37%  perf    [kernel.vmlinux]    [k] smp_call_function_single
>                |
>                ---smp_call_function_single
>                   _perf_event_enable
>                   perf_event_for_each_child
>                   perf_ioctl
>                   do_vfs_ioctl
>                   sys_ioctl
>                   entry_SYSCALL_64_fastpath
>                   __GI___ioctl
>                   0
>                   0
>                   0x1c5aa70
>                   0x1c5b910
>                   0x1c5aa70
>                   0x1c5b910
>                   0x1c5aa70
>                   0x1c5b910
>                   0x1c5aa70
>                   0x1c5b910
>                   0x1c5aa70
>                   0x1c5b910
> 		  ...
> 
> After:
>   $ perf report --stdio --no-children -g callee
>   ...
> 
>    1.37%  perf    [kernel.vmlinux]    [k] smp_call_function_single
>                |
>                ---smp_call_function_single
>                   _perf_event_enable
>                   perf_event_for_each_child
>                   perf_ioctl
>                   do_vfs_ioctl
>                   sys_ioctl
>                   entry_SYSCALL_64_fastpath
>                   __GI___ioctl

In addition to that, would it make sense to terminate the callchain with an 
indicator that we found something anomalous? Such an extra line:

                    ...

would not be intrusive, but would tell the informed reader that it's not a normal 
ending of the call chain.

This assumes that we can tell apart 'normal end of call chain' from 'seems to end 
with garbage poiner' cases - can do we that?

Thanks,

	Ingo