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

[Ken Werner]

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.

Regards
Ken