On Tue, May 12, 2015 at 12:48:13PM +0100, Maninder Singh wrote:
> EP-2DAD0AFA905A4ACB804C4F82A001242F
>
> On ARM, when a watchpoint is registered using register_wide_hw_breakpoint,
> the callback handler endlessly runs until the watchpoint is unregistered.
> The reason for this issue is debug interrupts gets raised before executing
> the instruction,
> and after interrupt handling ARM tries to execute the same instruction again
> , which results
> in interrupt getting raised again.
>
> This patch fixes this issue by using KPROBES (getting the instruction
> executed and incrementing PC
> to next instruction).
>
> Signed-off-by: Vaneet Narang <v.nar...@samsung.com>
> Signed-off-by: Maninder Singh <maninder...@samsung.com>
> Reviewed-by: Amit Arora <amit.ar...@samsung.com>
> Reviewed-by: Ajeet Yadav <ajee...@samsung.com>
> ---
> arch/arm/kernel/hw_breakpoint.c | 18 ++++++++++++++++++
> 1 files changed, 18 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
> index dc7d0a9..ec72f86 100644
> --- a/arch/arm/kernel/hw_breakpoint.c
> +++ b/arch/arm/kernel/hw_breakpoint.c
> @@ -37,6 +37,9 @@
> #include <asm/hw_breakpoint.h>
> #include <asm/kdebug.h>
> #include <asm/traps.h>
> +#ifdef CONFIG_KPROBES
> +#include <linux/kprobes.h>
> +#endif
>
> /* Breakpoint currently in use for each BRP. */
> static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);
> @@ -757,6 +760,21 @@ static void watchpoint_handler(unsigned long addr,
> unsigned int fsr,
> */
> if (!wp->overflow_handler)
> enable_single_step(wp, instruction_pointer(regs));
> +#ifdef CONFIG_KPROBES
> + else {
> + struct kprobe kp;
> + unsigned long flags;
> +
> + arch_uninstall_hw_breakpoint(wp);
> + kp.addr = (kprobe_opcode_t *)instruction_pointer(regs);
> + if (!arch_prepare_kprobe(&kp)) {
> + local_irq_save(flags);
> + kp.ainsn.insn_singlestep(&kp, regs);
> + local_irq_restore(flags);
> + }
> + arch_install_hw_breakpoint(wp);
> + }
> +#endif
I don't think this is the right thing to do at all; the kernel already
handles step exceptions using mismatched breakpoints when there is no
overflow handler specified (e.g. using perf mem events). If you register a
handler (e.g. gdb via ptrace) then you have to handle the step yourself.
Will
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