[Bug gdb/19061] New: gdb-7.10 hangs/spins-on-cpu when debugging any program on Alpha

["klausman-glibc at schwarzvogel dot de" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=19061

            Bug ID: 19061
           Summary: gdb-7.10 hangs/spins-on-cpu when debugging any program
                    on Alpha
           Product: gdb
           Version: 7.10
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: klausman-glibc at schwarzvogel dot de
  Target Milestone: ---

7.9.1 works fine:

$ gdb /bin/ls
GNU gdb (Gentoo 7.9.1 vanilla) 7.9.1
[...]
This GDB was configured as "alpha-unknown-linux-gnu".
Reading symbols from /bin/ls...(no debugging symbols found)...done.
(gdb) run
Starting program: /bin/ls 
4405_alpha-sysctl-uac.patch      gcc-4.6.3.tbz2            secfix.patch
[...]
[Inferior 1 (process 27877) exited normally]
(gdb) quit

7.10:
gdb-7.10 $ gdb/gdb /bin/ls
GNU gdb (7.10-vanilla) 7.10
This GDB was configured as "alpha-unknown-linux-gnu".
Reading symbols from /bin/ls...(no debugging symbols found)...done.
(gdb) run
Starting program: /bin/ls 
[gdb hangs here, eating close to 100% of one CPU. straceing it yields nothing
immediately obvious.]

So I bisected this from the tagged gdb-7.xy-release commits, using the example
above as a test case. I found was this commit to be the first bad one:

faf09f0119da40d9b408021ad5665a906e00ee59 is the first bad commit
commit faf09f0119da40d9b408021ad5665a906e00ee59
Author: Pedro Alves <palves@redhat.com>
Date:   Wed Mar 4 20:41:16 2015 +0000

    Linux native: Use TRAP_BRKPT/TRAP_HWBPT

    This patch adjusts the native Linux target backend to tell the core
    whether a trap was caused by a breakpoint.

    It teaches the target to get that information out of the si_code of
    the SIGTRAP siginfo.

    Tested on x86-64 Fedora 20, s390 RHEL 7, and PPC64 Fedora 18.  An
    earlier version was tested on ARM Fedora 21.

    gdb/ChangeLog:
    2015-03-04  Pedro Alves  <palves@redhat.com>

        * linux-nat.c (save_sigtrap): Check for breakpoints before
        checking watchpoints.
        (status_callback) [USE_SIGTRAP_SIGINFO]: Don't check whether a
        breakpoint is inserted if relying on SIGTRAP's siginfo.si_code.
        (check_stopped_by_breakpoint) [USE_SIGTRAP_SIGINFO]: Decide whether
        a breakpoint triggered based on the SIGTRAP's siginfo.si_code.
        (linux_nat_stopped_by_sw_breakpoint)
        (linux_nat_supports_stopped_by_sw_breakpoint)
        (linux_nat_stopped_by_hw_breakpoint)
        (linux_nat_supports_stopped_by_hw_breakpoint): New functions.
        (linux_nat_wait_1): Don't re-increment the PC if relying on
        SIGTRAP's siginfo->si_code.
        (linux_nat_add_target): Install new target methods.
        * linux-thread-db.c (check_event): Don't account for breakpoint PC
        offset if the target already adjusted the PC.
        * nat/linux-ptrace.h (USE_SIGTRAP_SIGINFO): New.
        (GDB_ARCH_TRAP_BRKPT): New.
        (TRAP_HWBKPT): Define if not already defined.

:040000 040000 5623811c697afc352ad61c2090773eacf8b4fbbc
206b4d6974c8a35cbada87c5c9555e8558a798e4 M      gdb


I am unsure how to dig out the actual problem from this, but I can provide
access to an Alpha machine if need be.

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