[PATCH] AArch64: Add single-step and breakpoint handler hooks
Will Deacon
will.deacon at arm.com
Tue Aug 13 07:32:53 EDT 2013
On Tue, Aug 06, 2013 at 07:12:06AM +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
> pass the correct break/step address to the handlers, i.e. FAR_EL1 if
> exception is watchpoint, ELR_EL1 for all other debug exceptions.
>
> Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu at linaro.org>
> Signed-off-by: Deepak Saxena <dsaxena at linaro.org>
> ---
> arch/arm64/include/asm/debug-monitors.h | 20 +++++++
> arch/arm64/kernel/debug-monitors.c | 102 +++++++++++++++++++++++++++++++-
> arch/arm64/kernel/entry.S | 6 +-
> 3 files changed, 124 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h
> index a2232d0..aff3a76 100644
> --- a/arch/arm64/include/asm/debug-monitors.h
> +++ b/arch/arm64/include/asm/debug-monitors.h
> @@ -16,6 +16,8 @@
> #ifndef __ASM_DEBUG_MONITORS_H
> #define __ASM_DEBUG_MONITORS_H
>
> +#include <linux/list.h>
> +
> #ifdef __KERNEL__
>
> #define DBG_ESR_EVT(x) (((x) >> 27) & 0x7)
> @@ -62,6 +64,24 @@ struct task_struct;
>
> #define DBG_ARCH_ID_RESERVED 0 /* In case of ptrace ABI updates. */
>
> +struct step_hook {
> + struct list_head node;
> + int (*fn)(struct pt_regs *regs, unsigned int insn, unsigned long addr);
> +};
Shouldn't that be esr instead of insn?
> +void register_step_hook(struct step_hook *hook);
> +void unregister_step_hook(struct step_hook *hook);
> +
> +struct break_hook {
> + struct list_head node;
> + u32 esr_magic;
There's nothing magic about it. esr_val instead?
> + u32 esr_mask;
> + int (*fn)(struct pt_regs *regs, unsigned int insn, unsigned long addr);
> +};
> +
> +void register_break_hook(struct break_hook *hook);
> +void unregister_break_hook(struct break_hook *hook);
> +
> u8 debug_monitors_arch(void);
>
> void enable_debug_monitors(enum debug_el el);
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index cbfacf7..2846327 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -188,6 +188,54 @@ static void clear_regs_spsr_ss(struct pt_regs *regs)
> regs->pstate = spsr;
> }
>
> +/* EL1 Single Step Handler hooks */
> +static LIST_HEAD(step_hook);
> +static DEFINE_RAW_SPINLOCK(step_lock);
> +
> +void register_step_hook(struct step_hook *hook)
> +{
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave(&step_lock, flags);
> + list_add(&hook->node, &step_hook);
> + raw_spin_unlock_irqrestore(&step_lock, flags);
> +}
> +
> +void unregister_step_hook(struct step_hook *hook)
> +{
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave(&step_lock, flags);
> + list_del(&hook->node);
> + raw_spin_unlock_irqrestore(&step_lock, flags);
> +}
Why do you need to disable IRQs during these operations?
> +/*
> + * Call registered single step handers
> + * There is no Syndrome info to check for determining the handler.
> + * So we call all the registered handlers, until the right handler is
> + * found which returns zero.
> + */
> +static int call_step_hook(struct pt_regs *regs,
> + unsigned int esr, unsigned long addr)
> +{
> + struct step_hook *hook;
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave(&step_lock, flags);
> + list_for_each_entry(hook, &step_hook, node) {
> + raw_spin_unlock_irqrestore(&step_lock, flags);
Is this safe? Can't you stask the function pointer and break out of the loop
when you find it instead?
> + if (hook->fn(regs, esr, addr) == 0)
> + return 0;
> +
> + raw_spin_lock_irqsave(&step_lock, flags);
> + }
> + raw_spin_unlock_irqrestore(&step_lock, flags);
> +
> + return 1;
> +}
> +
> static int single_step_handler(unsigned long addr, unsigned int esr,
> struct pt_regs *regs)
> {
> @@ -215,8 +263,11 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
> */
> user_rewind_single_step(current);
> } else {
> - /* TODO: route to KGDB */
> - pr_warning("Unexpected kernel single-step exception at EL1\n");
> + /* Call single step handlers for kgdb/kprobes */
> + if (call_step_hook(regs, addr, esr) == 0)
> + return 0;
> +
> + pr_warn("unexpected single step exception at %lx!\n", addr);
> /*
> * Re-enable stepping since we know that we will be
> * returning to regs.
> @@ -227,11 +278,56 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
> return 0;
> }
>
> +
> +static LIST_HEAD(break_hook);
> +static DEFINE_RAW_SPINLOCK(break_lock);
> +
> +void register_break_hook(struct break_hook *hook)
> +{
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave(&break_lock, flags);
> + list_add(&hook->node, &break_hook);
> + raw_spin_unlock_irqrestore(&break_lock, flags);
> +}
> +
> +void unregister_break_hook(struct break_hook *hook)
> +{
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave(&break_lock, flags);
> + list_del(&hook->node);
> + raw_spin_unlock_irqrestore(&break_lock, flags);
> +}
> +
> +static int call_break_hook(struct pt_regs *regs,
> + unsigned int esr, unsigned long addr)
> +{
> + struct break_hook *hook;
> + unsigned long flags;
> + int (*fn)(struct pt_regs *regs,
> + unsigned int esr, unsigned long addr) = NULL;
> +
> + raw_spin_lock_irqsave(&break_lock, flags);
> + list_for_each_entry(hook, &break_hook, node)
> + if ((esr & hook->esr_mask) == hook->esr_magic)
> + fn = hook->fn;
> + raw_spin_unlock_irqrestore(&break_lock, flags);
That's better! (although I'm still unsure about the interrupts).
> + return fn ? fn(regs, esr, addr) : 1;
> +}
> +
> static int brk_handler(unsigned long addr, unsigned int esr,
> struct pt_regs *regs)
> {
> siginfo_t info;
>
> + /* Call single step handlers for kgdb/kprobes */
> + if (call_break_hook(regs, esr, addr) == 0)
> + return 0;
> +
> + pr_warn("unexpected brk exception at %lx, esr=0x%x\n", addr, esr);
> +
> if (!user_mode(regs))
> return -EFAULT;
>
> @@ -291,7 +387,7 @@ static int __init debug_traps_init(void)
> hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
> TRAP_HWBKPT, "single-step handler");
> hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
> - TRAP_BRKPT, "ptrace BRK handler");
> + TRAP_BRKPT, "AArch64 BRK handler");
Why change this name?
> return 0;
> }
> arch_initcall(debug_traps_init);
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 6ad781b..e7350bd 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -288,8 +288,12 @@ el1_dbg:
> /*
> * Debug exception handling
> */
> + mrs x25, far_el1 //far for watchpt
Useless comment. How about: "// Watchpoint location"?
> + cmp x24, #ESR_EL1_EC_WATCHPT_EL1
> + csel x0, x25, x22, eq //addr: x25->far_el1, x22->elr_el1
> + b.ge do_dbg
> tbz x24, #0, el1_inv // EL1 only
I'd rather you left the tbz as the first instruction in el1_dbg, then you
can also lose the b.ge.
Finally, I don't see the need for this patch until we have something like
kprobes or kgdb, so I'd rather hold off merging this additional support code
until we have a user for it.
Cheers,
Will
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