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Re: [Libunwind-devel] Problems with compiling libunwind on Ubuntu 10.04

From: Ken Werner
Subject: Re: [Libunwind-devel] Problems with compiling libunwind on Ubuntu 10.04
Date: Fri, 12 Aug 2011 14:24:02 +0200
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On 08/11/2011 05:28 AM, Ted Ts'o wrote:
On Wed, Aug 10, 2011 at 07:54:39PM -0700, Arun Sharma wrote:

These are known failures (functionality not implemented on x86_64
yet). But it shouldn't impact the common use cases (local unwinding).
The larger issue libunwind faces is due to APIs that call malloc or
ones which take locks:

* dl_iterate_phdr
* pthread_setspecific

The latter is easy to work around. The former requires a lock free,
malloc free implementation of dl_iterate_phdr.

The main use case I'm trying to implement is a signal handler that
dumps a stack trace to stderr, for use in environments where capturing
an core dump is not convenient/possible, so I don't think that should
be an issue.

Hm, I'm not sure. When calling unw_step from a signal handler you may encounter a dead lock because libunwind calls dl_iterate_phdr which isn't async signal safe. So, in case your code gets a signal during printf or something similar there is a window where the dl_iterate_phdr cannot acquire the lock and you're stuck.


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