Making libunwind the default

[Dridi Boukelmoune]

On Mon, Jul 6, 2020 at 10:36 PM Guillaume Quintard
<guillaume at varnish-software.com> wrote:
>
> Hi all,
>
> https://github.com/varnishcache/varnish-cache/pull/3052 was merged in September and I was wondering if we had enough feedback (or lack thereof) to make a decision and on making the libunwind dependency official.
>
> All the weeklies are being built with libunwind since the end of October, and the 6.4 packages on packagecloud. And the official alpine packages use it too, which isn't surprising as the change was made to accommodate the lack of proper libexecinfo for that platform.
>
> Notably, if Nils has some feedback about the more "exotic" platforms he uses, I'm interested!

Also some backtrace implementations like libexecinfo use GCC builtins [1,2]
that are documented [3] as unsafe:

> Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program.

Adding a new dependency by default might be worth it all things considered.

Dridi

[1] __builtin_frame_address
[2] __builtin_return_address
[3] https://gcc.gnu.org/onlinedocs/gcc/Return-Address.html