[RFC] [PATCH] Multiple kprobes at an address redux (take4)

[Ananth N Mavinakayanahalli <amavin at redhat dot com>]

Hi,

Here goes take4.

The only change between take3 and this patch is the exporting of the
(un)register_kprobe_single() interfaces, for low-level users. Jprobes
(un)registration now use these interfaces.


Regards,
Ananth

 include/linux/kprobes.h |    3 
 kernel/kprobes.c        |  166 ++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 165 insertions(+), 4 deletions(-)

diff -Naurp temp/linux-2.6.12-rc2/include/linux/kprobes.h linux-2.6.12-rc2/include/linux/kprobes.h
--- temp/linux-2.6.12-rc2/include/linux/kprobes.h	2005-04-13 10:17:04.000000000 -0400
+++ linux-2.6.12-rc2/include/linux/kprobes.h	2005-04-13 09:26:32.000000000 -0400
@@ -43,6 +43,9 @@ typedef int (*kprobe_fault_handler_t) (s
 struct kprobe {
 	struct hlist_node hlist;
 
+	/* list of kprobes for multi-handler support */
+	struct list_head list;
+
 	/* location of the probe point */
 	kprobe_opcode_t *addr;
 
diff -Naurp temp/linux-2.6.12-rc2/kernel/kprobes.c linux-2.6.12-rc2/kernel/kprobes.c
--- temp/linux-2.6.12-rc2/kernel/kprobes.c	2005-04-13 10:17:04.000000000 -0400
+++ linux-2.6.12-rc2/kernel/kprobes.c	2005-04-13 09:29:55.000000000 -0400
@@ -44,6 +44,7 @@ static struct hlist_head kprobe_table[KP
 
 unsigned int kprobe_cpu = NR_CPUS;
 static DEFINE_SPINLOCK(kprobe_lock);
+static struct kprobe *curr_kprobe;
 
 /* Locks kprobe: irqs must be disabled */
 void lock_kprobes(void)
@@ -73,7 +74,49 @@ struct kprobe *get_kprobe(void *addr)
 	return NULL;
 }
 
-int register_kprobe(struct kprobe *p)
+int aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe *kp;
+
+	list_for_each_entry(kp, &p->list, list) {
+		if (kp->pre_handler) {
+			curr_kprobe = kp;
+			kp->pre_handler(kp, regs);
+			curr_kprobe = NULL;
+		}
+	}
+	return 0;
+}
+
+void aggr_post_handler(struct kprobe *p, struct pt_regs *regs, 
+		unsigned long flags)
+{
+	struct kprobe *kp;
+
+	list_for_each_entry(kp, &p->list, list) {
+		if (kp->post_handler) {
+			curr_kprobe = kp;
+			kp->post_handler(kp, regs, flags);
+			curr_kprobe = NULL;
+		}
+	}
+	return;
+}
+
+int aggr_fault_handler(struct kprobe *p, struct pt_regs *regs, int trapnr)
+{
+	/* 
+	 * if we faulted "during" the execution of a user specified
+	 * probe handler, invoke just that probe's fault handler
+	 */ 
+	if (curr_kprobe && curr_kprobe->fault_handler) {
+		if (curr_kprobe->fault_handler(curr_kprobe, regs, trapnr))
+			return 1;
+	}
+	return 0;
+}
+
+static int register_kprobe_single(struct kprobe *p)
 {
 	int ret = 0;
 	unsigned long flags = 0;
@@ -104,7 +147,7 @@ rm_kprobe:
 	return ret;
 }
 
-void unregister_kprobe(struct kprobe *p)
+static void unregister_kprobe_single(struct kprobe *p)
 {
 	unsigned long flags;
 	arch_remove_kprobe(p);
@@ -116,6 +159,119 @@ void unregister_kprobe(struct kprobe *p)
 	spin_unlock_irqrestore(&kprobe_lock, flags);
 }
 
+static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
+{
+	ap->addr = p->addr;
+	ap->opcode = p->opcode;
+	memcpy(&ap->ainsn, &p->ainsn, 
+			sizeof(struct arch_specific_insn));
+
+	ap->pre_handler = aggr_pre_handler;
+	ap->post_handler = aggr_post_handler;
+	ap->fault_handler = aggr_fault_handler;
+
+	INIT_LIST_HEAD(&ap->list);
+	list_add(&p->list, &ap->list);
+
+	INIT_HLIST_NODE(&ap->hlist);
+	hlist_del(&p->hlist);
+	hlist_add_head(&ap->hlist,
+		&kprobe_table[hash_ptr(ap->addr,
+				KPROBE_HASH_BITS)]);
+}
+
+static int register_aggr_kprobe(struct kprobe *p)
+{
+	int ret = 0;
+	unsigned long flags = 0;
+	struct kprobe *old_p, *ap;
+
+	ap = kcalloc(1, sizeof(struct kprobe), GFP_KERNEL);
+	if (!ap) 
+		return -ENOMEM;
+
+	spin_lock_irqsave(&kprobe_lock, flags);
+	old_p = get_kprobe(p->addr);
+	if (old_p) {
+		if (old_p->break_handler || p->break_handler) {
+			ret = -EEXIST;
+			goto free_ap;
+		} else if (old_p->pre_handler == aggr_pre_handler) {
+			list_add(&p->list, &old_p->list);
+			goto free_ap;
+		} else {
+			add_aggr_kprobe(ap, old_p);
+			list_add(&p->list, &ap->list);
+			goto out;
+		}
+	} else {
+		/* 
+		 * kprobe at this addr was deleted between the check
+		 * in register_kprobe() and the get_kprobe() call above
+		 */
+		spin_unlock_irqrestore(&kprobe_lock, flags);
+		ret = register_kprobe_single(p);
+		if (ret == -EEXIST) {
+			spin_lock_irqsave(&kprobe_lock, flags);
+			old_p = get_kprobe(p->addr);
+			if (old_p) {
+				add_aggr_kprobe(ap, old_p);
+				list_add(&p->list, &ap->list);
+			}
+			goto out;
+		} else
+			kfree(ap);
+		return ret;
+	}
+free_ap:
+	kfree(ap);
+out:
+	spin_unlock_irqrestore(&kprobe_lock, flags);
+	return ret;
+}
+
+static void unregister_aggr_kprobe(struct kprobe *old_p, 
+		struct kprobe *p, unsigned long flags)
+{
+	/* we have taken the spinlock in unregister_kprobe() */
+	list_del(&p->list);
+
+	if (list_empty(&old_p->list)) {
+		spin_unlock_irqrestore(&kprobe_lock, flags);
+		unregister_kprobe_single(old_p);
+		kfree(old_p);
+		return;
+	} 
+	spin_unlock_irqrestore(&kprobe_lock, flags);
+}
+
+int register_kprobe(struct kprobe *p)
+{
+	int ret = 0;
+
+	ret = register_kprobe_single(p);
+	if (ret == -EEXIST) 
+		ret = register_aggr_kprobe(p);
+
+	return ret;
+}
+
+void unregister_kprobe(struct kprobe *p)
+{
+	unsigned long flags;
+	struct kprobe *old_p;
+
+	spin_lock_irqsave(&kprobe_lock, flags);
+	old_p = get_kprobe(p->addr);
+
+	if (old_p && (old_p->pre_handler == aggr_pre_handler))
+		unregister_aggr_kprobe(old_p, p, flags);
+	else if (old_p == p) {
+		spin_unlock_irqrestore(&kprobe_lock, flags);
+		unregister_kprobe_single(p);
+	}
+}
+
 static struct notifier_block kprobe_exceptions_nb = {
 	.notifier_call = kprobe_exceptions_notify,
 	.priority = 0x7fffffff /* we need to notified first */
@@ -127,12 +283,12 @@ int register_jprobe(struct jprobe *jp)
 	jp->kp.pre_handler = setjmp_pre_handler;
 	jp->kp.break_handler = longjmp_break_handler;
 
-	return register_kprobe(&jp->kp);
+	return register_kprobe_single(&jp->kp);
 }
 
 void unregister_jprobe(struct jprobe *jp)
 {
-	unregister_kprobe(&jp->kp);
+	unregister_kprobe_single(&jp->kp);
 }
 
 static int __init init_kprobes(void)
@@ -152,6 +308,8 @@ __initcall(init_kprobes);
 
 EXPORT_SYMBOL_GPL(register_kprobe);
 EXPORT_SYMBOL_GPL(unregister_kprobe);
+EXPORT_SYMBOL_GPL(register_kprobe_single);
+EXPORT_SYMBOL_GPL(unregister_kprobe_single);
 EXPORT_SYMBOL_GPL(register_jprobe);
 EXPORT_SYMBOL_GPL(unregister_jprobe);
 EXPORT_SYMBOL_GPL(jprobe_return);