Re: [Libunwind-devel] Re: Backtrace from signal handler on arm from threads

[Lassi Tuura]

Hi,

> Hmm.  Looking at it, it might seem like libpthread is lacking some
> symbols, creating problems.

Symbols don't affect unwinding, as far as I know.

> One thing, though:  For release software, we'd prefer to ship without
> debugging symbols.  I can accept that that means we have worse
> backtraces, but it's not particularly handy that the unwinding
> segfaults.  Is this hard to avoid?

See my other reply, you are dropping into frame-chain (= fallback) walk
code. It can be exceedingly hard to get that to work reliably. On x86_64
we added this to be very careful when in that piece of code:

   /* We could get here because of missing/bad unwind information.
      Validate all addresses before dereferencing. */
   c->validate = 1;

ARM code doesn't do that, though I don't know if ARM has validating memory
access calls in the first place. You might want to compare the code a bit.

Regards,
Lassi