[Bug gdb/16571] New: gdb can not work (linux aach64)

[Bug gdb/16571] New: gdb can not work (linux aach64)

[pla_456 at 163 dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16571

            Bug ID: 16571
           Summary: gdb can not work (linux aach64)
           Product: gdb
           Version: 7.6
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: pla_456 at 163 dot com

os: Linux ma1arms4 3.12.0-0.rc4.git0.1.x2.fc19.aarch64 #1 SMP Wed Oct 9
13:50:50 EDT 2013 aarch64 aarch64 aarch64 GNU/Linux

error msg:

(gdb) n
[New process 12478]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[Switching to Thread 0x7fb7fef000 (LWP 12478)]
0x0000007fb7dc1964 in fork () from /lib64/libc.so.6
Unexpected error setting hardware debug registers

gdb version:
GNU gdb (GDB) Fedora 7.6.1-41.fc19
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "aarch64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.

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[Bug gdb/16571] gdb can not work (linux aach64)

[will.newton at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16571

Will Newton <will.newton at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |will.newton at gmail dot com
         Resolution|---                         |FIXED

--- Comment #1 from Will Newton <will.newton at gmail dot com> ---

This issue is fixed in gdb 7.8, but you also must make sure you have a recent
kernel with this commit:

commit cdc27c27843248ae7eb0df5fc261dd004eaa5670
Author: Will Deacon <will.deacon@arm.com>
Date:   Tue Dec 17 17:09:08 2013 +0000

    arm64: ptrace: avoid using HW_BREAKPOINT_EMPTY for disabled events

    Commit 8f34a1da35ae ("arm64: ptrace: use HW_BREAKPOINT_EMPTY type for
    disabled breakpoints") fixed an issue with GDB trying to zero breakpoint
    control registers. The problem there is that the arch hw_breakpoint code
    will attempt to create a (disabled), execute breakpoint of length 0.

    This will fail validation and report unexpected failure to GDB. To avoid
    this, we treated disabled breakpoints as HW_BREAKPOINT_EMPTY, but that
    seems to have broken with recent kernels, causing watchpoints to be
    treated as TYPE_INST in the core code and returning ENOSPC for any
    further breakpoints.

    This patch fixes the problem by prioritising the `enable' field of the
    breakpoint: if it is cleared, we simply update the perf_event_attr to
    indicate that the thing is disabled and don't bother changing either the
    type or the length. This reinforces the behaviour that the breakpoint
    control register is essentially read-only apart from the enable bit
    when disabling a breakpoint.

    Cc: <stable@vger.kernel.org>
    Reported-by: Aaron Liu <liucy214@gmail.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

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