toolchain/56330: amd64 gdb issues

[dholland%NetBSD.org@localhost]

>Number:         56330
>Category:       toolchain
>Synopsis:       amd64 gdb issues
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jul 25 04:30:00 +0000 2021
>Originator:     David A. Holland
>Release:        NetBSD 9.99.85 (20210623)
>Organization:
>Environment:
System: NetBSD valkyrie 9.99.85 NetBSD 9.99.85 (VALKYRIE) #7: Wed Jun 23 18:32:25 EDT 2021  dholland@valkyrie:/usr/src/sys/arch/amd64/compile/VALKYRIE amd64
Architecture: x86_64
Machine: amd64
>Description:

1. Debugging multithreaded processes in gdb doesn't work. I can run
the target and set breakpoints, but any attempt to step or next
immediately stops with SIGTRAP in ___lwp_park60, and if you continue
trying eventually the target segfaults.

2. About a third of the time or so, killing the target causes gdb to
hang. ps -s shows one thread with wchan "wait", and a bunch of others
"parked". The target is stopped. (This may only happen with
multithreaded processes, not sure.)

3. A whole stack of ptrace tests are currently failing in the testbed;
it's likely this is the root cause.

>How-To-Repeat:
>Fix: