[Libunwind-devel] Arm: issue of reading SP register

[MyungJoo Ham]

Hello,


I have been tracking stack unwinding issues for stacks created by CPP
and Assemblies in ARM and found that relying on dwarf->cfa in
src/arm/Gregs.c for SP register has a problem when we are trying to
unwind to a stack that is not supposed to be DWARF compatible
from a stack what is compatible.
https://github.com/dotnet/coreclr/issues/3309


The issue was easilly mitigated by allowing reading SP from SP, not from CFA.
Besides, ARM-DWARF has a big problem of not properly allowing falling back
from a failed trial of DWARF unwinding, which forces me to disable DWARF usage
in ARM-Linux machines. (when DWARF fails, it is supposed to try other two
methods, which fail because DWARF-trial has contaminated required data 
structures:
they succeed if DWARF is skipped.)

In order to bypass such issues, I suggest the following patch,
which is going to be posted as "reply" to this message.


Cheers,
MyungJoo