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    SubjectRe: [PATCH RFC v4 1/6] arm64: support single-step and breakpoint handler hooks
    Hi Sandeepa,

    This is getting there, thanks for persevering with it. I still have a few
    minor comments though.

    On Thu, Oct 17, 2013 at 12:17:46PM +0100, Sandeepa Prabhu wrote:
    > AArch64 Single Steping and Breakpoint debug exceptions will be
    > used by multiple debug framworks like kprobes & kgdb.
    >
    > This patch implements the hooks for those frameworks to register
    > their own handlers for handling breakpoint and single step events.
    >
    > Reworked the debug exception handler in entry.S: do_dbg to route
    > software breakpoint (BRK64) exception to do_debug_exception()
    >
    > Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
    > Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
    > ---
    > arch/arm64/include/asm/debug-monitors.h | 21 ++++++++
    > arch/arm64/kernel/debug-monitors.c | 86 ++++++++++++++++++++++++++++++++-
    > arch/arm64/kernel/entry.S | 2 +
    > 3 files changed, 108 insertions(+), 1 deletion(-)

    [...]

    > @@ -215,7 +257,10 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
    > */
    > user_rewind_single_step(current);
    > } else {
    > - /* TODO: route to KGDB */
    > + /* call registered single step handlers */

    Don't bother with this comment (it's crystal clear from the code).

    > + if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
    > + return 0;
    > +
    > pr_warning("Unexpected kernel single-step exception at EL1\n");
    > /*
    > * Re-enable stepping since we know that we will be
    > @@ -227,11 +272,50 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
    > return 0;
    > }
    >
    > +
    > +static LIST_HEAD(break_hook);
    > +DEFINE_RWLOCK(break_hook_lock);

    This guy can be a plain old spinlock. That way, the readers have less
    overhead but things still work because we only call a single hook function.

    Will


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