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

["will.newton at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

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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