[Bug 1908756] [NEW] Ubuntu 20.10 - elfutils unwinding broken for s390 compat

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---Problem Description---
libdw unwinding fails for 32 bit binaries.
 
Elfutils biarch test currently fails on s390x doing unwinding for a 32 bit process.

FAIL: run-backtrace-native-biarch.sh
====================================

0x557e7000      0x557eb000      /root/elfutils/tests/backtrace-child-biarch
0x7dba4000      0x7dd51000      /usr/lib/libc-2.32.so
0x7dd53000      0x7dd70000      /usr/lib/libpthread-2.32.so
0x7dd7f000      0x7dda6000      /usr/lib/ld-2.32.so
TID 376858:
# 0 0x7dd6668a          raise
# 1 0x7fd0ef60 - 1      <null>
/root/elfutils/tests/backtrace: dwfl_thread_getframes: No DWARF information found
backtrace: backtrace.c:114: callback_verify: Assertion `symname != NULL && strcmp (symname, "sigusr2") == 0' failed.
./test-subr.sh: line 84: 376822 Aborted                 (core dumped) LD_LIBRARY_PATH="${built_library_path}${LD_LIBRARY_PATH:+:}$LD_LIBRARY_PATH" $VALGRIND_CMD "$@"
backtrace-child-biarch: no main
FAIL run-backtrace-native-biarch.sh (exit status: 1)

Patch has already been posted and upstream committed:
https://sourceware.org/pipermail/elfutils-devel/2020q4/003149.html

Please pick up the following commit for the next release:
commit e4d985a3c1c873f77d20fa0cd421458cc2824996
Author: Andreas Krebbel <krebbel at linux.ibm.com>
Date:   Thu Nov 19 20:32:24 2020 +0100

    IBM Z: Fix endianess problem in pid_memory_read
    
    The cached reads lack the big endian adjustments done in the fallback
    path.
    
    Signed-off-by: Andreas Krebbel <krebbel at linux.ibm.com>


The patch applies cleanly ontop of elfutils_0.181-1.

====
strace right now is not built with unwinding support for IBM Z although both variants should work - libdw and libunwind.

Other distros use libdw from elfutils while Ubuntu on x86 appears to use
libunwind. libdw and libunwind do support IBM Z.

It would be good to build strace with unwinding support for Z.

** Affects: elfutils (Ubuntu)
     Importance: Undecided
     Assignee: Skipper Bug Screeners (skipper-screen-team)
         Status: New


** Tags: architecture-s39064 bugnameltc-190488 severity-medium targetmilestone-inin2104
-- 
Ubuntu 20.10 - elfutils unwinding broken for s390 compat
https://bugs.launchpad.net/bugs/1908756
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