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Subject[PATCH RFC v4 1/6] arm64: support single-step and breakpoint handler hooks
Date
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(-)

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
--
1.8.1.2


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