[Bug backtrace/31294] New: cant unwind __libc_do_syscall from gcore in arm 32 bits

["blarsen at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31294

            Bug ID: 31294
           Summary: cant unwind __libc_do_syscall from gcore in arm 32
                    bits
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: backtrace
          Assignee: unassigned at sourceware dot org
          Reporter: blarsen at redhat dot com
  Target Milestone: ---

The newly introduced test gdb.threads/threadcrash.exp has revealed a
pre-existing issue in 32 bit arm.

using "info threads" on a regular corefile gives the following thread list:

info threads
  Id   Target Id                      Frame 
* 1    Thread 0xf7dbe7e0 (LWP 476389) 0x00830cea in crash_function () at
/home/tcwg-buildslave/workspace/tcwg_gnu_4/abe/snapshots/gdb.git~master/gdb/testsuite/gdb.threads/threadcrash.c:381
  2    Thread 0xf7c6f3a0 (LWP 476390) do_spin_task (location=NORMAL) at
/home/tcwg-buildslave/workspace/tcwg_gnu_4/abe/snapshots/gdb.git~master/gdb/testsuite/gdb.threads/threadcrash.c:139
  3    Thread 0xf746e3a0 (LWP 476391) do_spin_task (location=SIGNAL_HANDLER) at
/home/tcwg-buildslave/workspace/tcwg_gnu_4/abe/snapshots/gdb.git~master/gdb/testsuite/gdb.threads/threadcrash.c:139
  4    Thread 0xf6c6d3a0 (LWP 476392) do_spin_task (location=SIGNAL_ALT_STACK)
at
/home/tcwg-buildslave/workspace/tcwg_gnu_4/abe/snapshots/gdb.git~master/gdb/testsuite/gdb.threads/threadcrash.c:139
  5    Thread 0xf52fe3a0 (LWP 476395) __libc_do_syscall () at
../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46
  6    Thread 0xf646c3a0 (LWP 476393) __libc_do_syscall () at
../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46
  7    Thread 0xf5aff3a0 (LWP 476394) __libc_do_syscall () at
../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46

Whereas the same command when loading a gcore yields:

info threads
  Id   Target Id         Frame 
* 1    LWP 476440        0x00400cea in crash_function () at
/home/tcwg-buildslave/workspace/tcwg_gnu_4/abe/snapshots/gdb.git~master/gdb/testsuite/gdb.threads/threadcrash.c:381
  2    LWP 476442        do_spin_task (location=NORMAL) at
/home/tcwg-buildslave/workspace/tcwg_gnu_4/abe/snapshots/gdb.git~master/gdb/testsuite/gdb.threads/threadcrash.c:139
  3    LWP 476443        do_spin_task (location=SIGNAL_HANDLER) at
/home/tcwg-buildslave/workspace/tcwg_gnu_4/abe/snapshots/gdb.git~master/gdb/testsuite/gdb.threads/threadcrash.c:139
  4    LWP 476444        do_spin_task (location=SIGNAL_ALT_STACK) at
/home/tcwg-buildslave/workspace/tcwg_gnu_4/abe/snapshots/gdb.git~master/gdb/testsuite/gdb.threads/threadcrash.c:139
  5    LWP 476445        0xf7eadb04 in ?? ()
  6    LWP 476446        0xf7eadb04 in ?? ()
  7    LWP 476447        0xf7eadb04 in ?? ()

Notice how the threads are in the same order, and threads 5, 6 and 7 all fail
the unwinding. This can be shown in the Linaro CI bug GNU-1120[1], even though
the main focus of the bug is unrelated to this.

I'm opening this mostly as a papertrail to add a KFAIL to the test, but it
should probably be fixed at some point.

[1] https://linaro.atlassian.net/browse/GNU-1120

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