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    Subject[PATCH 1/2] powerpc/hw_breakpoint: move instruction stepping out of hw_breakpoint_handler()
    Date
    From: Christophe Leroy <christophe.leroy@c-s.fr>

    On 8xx, breakpoints stop after executing the instruction, so
    stepping/emulation is not needed. Move it into a sub-function and
    remove the #ifdefs.

    Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
    Reviewed-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
    ---
    arch/powerpc/kernel/hw_breakpoint.c | 60 ++++++++++++++++-------------
    1 file changed, 33 insertions(+), 27 deletions(-)

    diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
    index c8d1fa2e9d53..28ad3171bb82 100644
    --- a/arch/powerpc/kernel/hw_breakpoint.c
    +++ b/arch/powerpc/kernel/hw_breakpoint.c
    @@ -198,15 +198,43 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
    /*
    * Handle debug exception notifications.
    */
    +static bool stepping_handler(struct pt_regs *regs, struct perf_event *bp,
    + unsigned long addr)
    +{
    + int stepped;
    + unsigned int instr;
    +
    + /* Do not emulate user-space instructions, instead single-step them */
    + if (user_mode(regs)) {
    + current->thread.last_hit_ubp = bp;
    + regs->msr |= MSR_SE;
    + return false;
    + }
    +
    + stepped = 0;
    + instr = 0;
    + if (!__get_user_inatomic(instr, (unsigned int *)regs->nip))
    + stepped = emulate_step(regs, instr);
    +
    + /*
    + * emulate_step() could not execute it. We've failed in reliably
    + * handling the hw-breakpoint. Unregister it and throw a warning
    + * message to let the user know about it.
    + */
    + if (!stepped) {
    + WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
    + "0x%lx will be disabled.", addr);
    + perf_event_disable_inatomic(bp);
    + return false;
    + }
    + return true;
    +}
    +
    int hw_breakpoint_handler(struct die_args *args)
    {
    int rc = NOTIFY_STOP;
    struct perf_event *bp;
    struct pt_regs *regs = args->regs;
    -#ifndef CONFIG_PPC_8xx
    - int stepped = 1;
    - unsigned int instr;
    -#endif
    struct arch_hw_breakpoint *info;
    unsigned long dar = regs->dar;

    @@ -251,31 +279,9 @@ int hw_breakpoint_handler(struct die_args *args)
    (dar - bp->attr.bp_addr < bp->attr.bp_len)))
    info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;

    -#ifndef CONFIG_PPC_8xx
    - /* Do not emulate user-space instructions, instead single-step them */
    - if (user_mode(regs)) {
    - current->thread.last_hit_ubp = bp;
    - regs->msr |= MSR_SE;
    + if (!IS_ENABLED(CONFIG_PPC_8xx) && !stepping_handler(regs, bp, info->address))
    goto out;
    - }
    -
    - stepped = 0;
    - instr = 0;
    - if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
    - stepped = emulate_step(regs, instr);

    - /*
    - * emulate_step() could not execute it. We've failed in reliably
    - * handling the hw-breakpoint. Unregister it and throw a warning
    - * message to let the user know about it.
    - */
    - if (!stepped) {
    - WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
    - "0x%lx will be disabled.", info->address);
    - perf_event_disable_inatomic(bp);
    - goto out;
    - }
    -#endif
    /*
    * As a policy, the callback is invoked in a 'trigger-after-execute'
    * fashion
    --
    2.21.0
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