[musl] Better backtrace from core dump

[Michal Nowak <mnowak@isc.org>]

Hi,

in GitLab we have jobs which run BIND system tests on different 
operating system, mostly in Docker on Debian 10 but too in KVM virtual 
machines for non-Linux operating systems. If the test produces core 
dump, we generate backtrace out of it while still in the CI.

For all C libraries but for musl we get reasonable backtraces, e.g. 
https://gitlab.isc.org/isc-projects/bind9/-/jobs/970585, but for Alpine 
Linux 3.11 (musl 1.1.24-r2 & GCC 9.2.0-r4) we get something like this 
(https://gitlab.isc.org/isc-projects/bind9/-/jobs/970568):

warning: Can't read pathname for load map: No error information.
Core was generated by 
`/builds/isc-projects/bind9/bin/named/.libs/lt-named -D statistics-ns3 
-X named.'.
Program terminated with signal SIGABRT, Aborted.
#0  0x00007fb708ec39ee in setjmp () from /lib/ld-musl-x86_64.so.1
[Current thread is 1 (LWP 1274)]
#0  0x00007fb708ec39ee in setjmp () from /lib/ld-musl-x86_64.so.1
#1  0x00007fb708ec3b49 in raise () from /lib/ld-musl-x86_64.so.1
#2  0x804ad6685d596f46 in ?? ()
#3  0x00007fb708bd1030 in ns_modules () from 
/builds/isc-projects/bind9/lib/ns/.libs/libns.so.1702
#4  0x00007fb708e59edf in ?? () from 
/builds/isc-projects/bind9/lib/isc/.libs/libisc.so.1702
#5  0x0000000042756621 in ?? ()
#6  0x00007fb7069c9db0 in ?? ()
#7  0x0000001800000018 in ?? ()
#8  0x00007fb708f0e873 in ?? () from /lib/ld-musl-x86_64.so.1
#9  0x0000000000000008 in ?? ()
#10 0x00007fb7069ca0e8 in ?? ()
#11 0x00007fb7069ca0d0 in ?? ()
#12 0x00007fb708e32d12 in isc_hash_function (data=0x459, length=0, 
case_sensitive=<optimized out>) at hash.c:117

This is how we generate the backtrace:

   "${top_builddir}/libtool" --mode=execute gdb --batch 
--command=run.gdb --core="$coredump" -- "$binary"

The GDB command can be either 'bt' or 'thread apply all bt full' (for 
more on the GDB invocation, see 
https://gitlab.isc.org/isc-projects/bind9/-/blob/main/bin/tests/system/run.sh.in#L268).

CFLAGS used:

   -fno-omit-frame-pointer -fno-optimize-sibling-calls -O1 -g -Wall -Wextra

This is what we install on top of the stock Alpine Linux 3.11 Docker 
image: 
https://gitlab.isc.org/isc-projects/images/-/blob/main/docker/bind9/alpine-template/Dockerfile. 
Are there other packages, we should get into the image to get better 
backtraces?

Should we use something else than GDB?

Should we add some compiler flags?

Thanks,
Michal