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Date: Fri, 23 Aug 2019 16:21:44 +0200
From: Florian Weimer <fweimer@...hat.com>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com
Subject: Re: libexecinfo with musl

* Rich Felker:

> backtrace should not require any "support from libc". My guess at
> what's happening is that it fails to trace past main's stack frame
> back into the call point in libc startup code, since libc lacks unwind
> info. A working backtrace implementation needs to be prepared for this
> possibility and stop if it reaches back to an address without unwind
> info.

Depending on the architecture, this is impossible because some ABIs
mandate that the unwinder behaves in certain ways (other than stopping)
if a frame does not have explicit unwind information.  For example, they
could assume that the frame has a frame pointer, or that the stack
pointer has not been changed.  For example, my understanding is that for
POWER, the unwinder must assume that the function has a back chain if
the function lacks explicit unwind data.

Thanks,
Florian

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