Re: A scenario where Perf cannot unwind the user stack by dwarf with libdw.so

[Mark Wielaard <mark@klomp.org>]

Hi,

On Thu, 2023-02-16 at 23:48 +0100, Mark Wielaard wrote:
> On Mon, Feb 13, 2023 at 01:44:39AM +0000, liuxu (AJ) via Elfutils-devel wrote:
> > I am failing to unwind the user stack with libdw on Ubuntu 18.04
> > arm64 environment, the toolchain used is clang 12.0.1.  form the
> > unwinding process, I found that the pc value passing to handle_cfi
> > is 0x760, which is 0x10000 offset from the corresponding cfi address
> > 0x10760.
> > 
> > Futher analysis show that the bias calculated in
> > __libdwfl_elf_address_range for ET_DYN type pick the first PT_LOAD
> > segment, not the segment corresponds to code segment. So the bias
> > result is wrong in current situation.
> 
> I have some problem replicating this because I don't have the same
> toolchain and don't know enough about perf to know how to replicate.

We have discussed this a bit more offlist. But I still haven't been
able to replicate this issue. It seems to depend on a couple of things
I don't fully understand, clang, lld, musl, PIE executables, whether
the fallback frame based unwinder can/is used, etc.

I am hoping someone can sent me a binary to investigate.

Thanks,

Mark