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Re: [Libunwind-devel] unwinding from signal handler (ARM)

From: Ken Werner
Subject: Re: [Libunwind-devel] unwinding from signal handler (ARM)
Date: Fri, 19 Aug 2011 17:24:54 +0200
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On 08/19/2011 04:53 PM, Ken Werner wrote:
On 08/19/2011 02:39 PM, Sven Neumann wrote:
Now I've updated libunwind to 1.0-rc1 and this trick doesn't seem to
work any longer. The code appears to crash in libunwind if used as
above. I had a look at the ARM implementation and found that there is
now code that's supposed to unw_step a signal handler. So I tried
without our hack and just use unw_getcontext(). Now it doesn't crash any
longer, but it also doesn't unwind over the signal handler. All I get is
a stack trace like this:

0x4016cde0 logUnwind() from /usr/lib/
0x40205654 ?? from /usr/lib/

Any ideas what we could do?

Hmm, this is interesting. How does your system look like (which libc,
kernel version) and are you stepping over RT or non-RT signal frames? It
would be helpful if you could share some code that shows the described
In the meanwhile I'll prepare a simple testcase where I'll verify that
it's working on my system.

Attached is a simple testcase that works on my PandaBoard. How does it look on your system? The output should look like this:
  standard frame        ip:     0x8988, sp: 0xbeffadd0   sig_handler
  signal frame  ip: 0x40113740, sp: 0xbefff2f0   __default_rt_sa_restorer_v2
  standard frame        ip:     0x8c4e, sp: 0xbefff660   main
  standard frame        ip: 0x40104623, sp: 0xbefff668   __libc_start_main
  standard frame        ip:     0x88b7, sp: 0xbefff7a8   _start

The ARMv7 board runs a Linaro evaluation build with a fairly recent Linux kernel and glibc (


PS: I'll be on vacation for a few days starting tomorrow - bad timing. But I'll follow the discussion afterwards.

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