From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arun Sharma <asharma@fb.com>
Subject: Re: [PATCH] perf, x86: Disable sanity check
Date: Thu, 19 Apr 2012 10:33:32 -0700
Message-ID: <4F904C6C.7020407@fb.com>
References: <1334791449-402-1-git-send-email-asharma@fb.com> <20120419052208.GA29875@somewhere.redhat.com>
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To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>, Arnaldo Carvalho de Melo <acme@redhat.com>, Mike Galbraith <efault@gmx.de>, Paul Mackerras <paulus@samba.org>, Peter Zijlstra <peterz@infradead.org>, Stephane Eranian <eranian@google.com>, Namhyung Kim <namhyung.kim@lge.com>, Tom Zanussi <tzanussi@gmail.com>, linux-perf-users@vger.kernel.org

On 4/18/12 10:22 PM, Frederic Weisbecker wrote:

> 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.

Nothing specific to JITs here. Any time an app has two stacks S1 and S2 
(with S1 at a lower address and S2 at a higher address) and %rsp at the 
time of a perf event is pointing to S2, we don't get traces beyond S2.

               |                 |
               |                 |
               |   0x1000000     |  <-- %rbp
               |                 |
               |                 |
S2: 0x2000000 |                 |  <-- %rsp
               |                 |
               |                 |
               |                 |
               |    frame3       |
               |                 |
               |    frame2       |
               |                 |
S1: 0x1000000 |    frame1       |
               |                 |
               |                 |
               |                 |
               |                 |

gdb is able to show:

(gdb) bt
<frame at 0x2000000>
frame1
frame2
frame3
frame4
..

just fine.

In our use case, there may be multiple transitions between S1 and S2. 
For eg: frame4 could be on S2 (i.e 0x2xxxxxx range).

  -Arun