diff mbox

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

Message ID 1382008671-4515-2-git-send-email-sandeepa.prabhu@linaro.org (mailing list archive)
State New, archived
Headers show

Commit Message

Sandeepa Prabhu Oct. 17, 2013, 11:17 a.m. UTC
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(-)

Comments

Will Deacon Oct. 25, 2013, 3:22 p.m. UTC | #1
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
Sandeepa Prabhu Dec. 3, 2013, 2:33 p.m. UTC | #2
Hi Will,

Sorry for responding to this after long-time, I missed this review
during Linaro connect travels.

On 25 October 2013 20:52, Will Deacon <will.deacon@arm.com> wrote:
> 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).
OK, I will remove this unnecessary print.
>
>> +             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.
well, kprobes need to support recursive breakpoints (i.e. breakpoint
handler executing BRK once again)
so I converted this lock to rw_lock.  I should put this info in commit
description to be more clearer.
Let me know if you find any issue with re-cursing in breakpoint exception?

Thanks,
Sandeepa
>
> Will
> --
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Will Deacon Dec. 3, 2013, 7:44 p.m. UTC | #3
On Tue, Dec 03, 2013 at 02:33:17PM +0000, Sandeepa Prabhu wrote:
> Hi Will,
> 
> Sorry for responding to this after long-time, I missed this review
> during Linaro connect travels.

No problem.

> >> @@ -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).
> OK, I will remove this unnecessary print.

Thanks.

> >> +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.
> well, kprobes need to support recursive breakpoints (i.e. breakpoint
> handler executing BRK once again)
> so I converted this lock to rw_lock.  I should put this info in commit
> description to be more clearer.

Actually, this is one place where a comment in the code *would* be useful!

> Let me know if you find any issue with re-cursing in breakpoint exception?

Sounds ok to me. With those changes:

  Acked-by: Will Deacon <will.deacon@arm.com>

Cheers,

Will
diff mbox

Patch

diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h
index a2232d0..6231479 100644
--- a/arch/arm64/include/asm/debug-monitors.h
+++ b/arch/arm64/include/asm/debug-monitors.h
@@ -62,6 +62,27 @@  struct task_struct;
 
 #define DBG_ARCH_ID_RESERVED	0	/* In case of ptrace ABI updates. */
 
+#define DBG_HOOK_HANDLED	0
+#define DBG_HOOK_ERROR		1
+
+struct step_hook {
+	struct list_head node;
+	int (*fn)(struct pt_regs *regs, unsigned int esr);
+};
+
+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_val;
+	u32 esr_mask;
+	int (*fn)(struct pt_regs *regs, unsigned int esr);
+};
+
+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..e42ad5f 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -188,6 +188,48 @@  static void clear_regs_spsr_ss(struct pt_regs *regs)
 	regs->pstate = spsr;
 }
 
+/* EL1 Single Step Handler hooks */
+static LIST_HEAD(step_hook);
+DEFINE_RWLOCK(step_hook_lock);
+
+void register_step_hook(struct step_hook *hook)
+{
+	write_lock(&step_hook_lock);
+	list_add(&hook->node, &step_hook);
+	write_unlock(&step_hook_lock);
+}
+
+void unregister_step_hook(struct step_hook *hook)
+{
+	write_lock(&step_hook_lock);
+	list_del(&hook->node);
+	write_unlock(&step_hook_lock);
+}
+
+/*
+ * 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)
+{
+	struct step_hook *hook;
+	int retval = DBG_HOOK_ERROR;
+
+	read_lock(&step_hook_lock);
+
+	list_for_each_entry(hook, &step_hook, node)	{
+		retval = hook->fn(regs, esr);
+		if (retval == DBG_HOOK_HANDLED)
+			break;
+	}
+
+	read_unlock(&step_hook_lock);
+
+	return retval;
+}
+
 static int single_step_handler(unsigned long addr, unsigned int esr,
 			       struct pt_regs *regs)
 {
@@ -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 */
+		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);
+
+void register_break_hook(struct break_hook *hook)
+{
+	write_lock(&break_hook_lock);
+	list_add(&hook->node, &break_hook);
+	write_unlock(&break_hook_lock);
+}
+
+void unregister_break_hook(struct break_hook *hook)
+{
+	write_lock(&break_hook_lock);
+	list_del(&hook->node);
+	write_unlock(&break_hook_lock);
+}
+
+static int call_break_hook(struct pt_regs *regs, unsigned int esr)
+{
+	struct break_hook *hook;
+	int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
+
+	read_lock(&break_hook_lock);
+	list_for_each_entry(hook, &break_hook, node)
+		if ((esr & hook->esr_mask) == hook->esr_val)
+			fn = hook->fn;
+	read_unlock(&break_hook_lock);
+
+	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
+}
+
 static int brk_handler(unsigned long addr, unsigned int esr,
 		       struct pt_regs *regs)
 {
 	siginfo_t info;
 
+	/* call the registered breakpoint handler */
+	if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
+		return 0;
+
+	pr_warn("unexpected brk exception at %lx, esr=0x%x\n",
+			(long)instruction_pointer(regs), esr);
+
 	if (!user_mode(regs))
 		return -EFAULT;
 
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 3881fd1..7fbc510 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -288,6 +288,8 @@  el1_dbg:
 	/*
 	 * Debug exception handling
 	 */
+	cmp	x24, #ESR_EL1_EC_BRK64		// if BRK64
+	cinc	x24, x24, eq			// set bit '0'
 	tbz	x24, #0, el1_inv		// EL1 only
 	mrs	x0, far_el1
 	mov	x2, sp				// struct pt_regs