[PATCH 3/3] kprobes: kretprobes simplifcations

From: Christoph Hellwig
Date: Sat Mar 31 2007 - 10:00:12 EST

- consolidate duplicate code in all arch_prepare_kretprobe instances
into common code
- replace various odd helpers that use hlist_for_each_entry to get
the first elemenet of a list with either a hlist_for_each_entry_save
or an opencoded access to the first element in the caller
- inline add_rp_inst into it's only remaining caller
- use kretprobe_inst_table_head instead of opencoding it


Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Index: linux-2.6/arch/i386/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/arch/i386/kernel/kprobes.c 2007-03-31 14:31:24.000000000 +0200
+++ linux-2.6/arch/i386/kernel/kprobes.c 2007-03-31 14:47:40.000000000 +0200
@@ -226,24 +226,15 @@ static void __kprobes prepare_singlestep
}

/* Called with kretprobe_lock held */
-void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
unsigned long *sara = (unsigned long *)&regs->esp;

- struct kretprobe_instance *ri;
+ ri->ret_addr = (kprobe_opcode_t *) *sara;

- if ((ri = get_free_rp_inst(rp)) != NULL) {
- ri->rp = rp;
- ri->task = current;
- ri->ret_addr = (kprobe_opcode_t *) *sara;
-
- /* Replace the return addr with trampoline addr */
- *sara = (unsigned long) &kretprobe_trampoline;
- add_rp_inst(ri);
- } else {
- rp->nmissed++;
- }
+ /* Replace the return addr with trampoline addr */
+ *sara = (unsigned long) &kretprobe_trampoline;
}

/*
Index: linux-2.6/arch/ia64/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/arch/ia64/kernel/kprobes.c 2007-03-31 14:31:24.000000000 +0200
+++ linux-2.6/arch/ia64/kernel/kprobes.c 2007-03-31 14:35:39.000000000 +0200
@@ -464,23 +464,13 @@ int __kprobes trampoline_probe_handler(s
}

/* Called with kretprobe_lock held */
-void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
- struct kretprobe_instance *ri;
+ ri->ret_addr = (kprobe_opcode_t *)regs->b0;

- if ((ri = get_free_rp_inst(rp)) != NULL) {
- ri->rp = rp;
- ri->task = current;
- ri->ret_addr = (kprobe_opcode_t *)regs->b0;
-
- /* Replace the return addr with trampoline addr */
- regs->b0 = ((struct fnptr *)kretprobe_trampoline)->ip;
-
- add_rp_inst(ri);
- } else {
- rp->nmissed++;
- }
+ /* Replace the return addr with trampoline addr */
+ regs->b0 = ((struct fnptr *)kretprobe_trampoline)->ip;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
Index: linux-2.6/arch/powerpc/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/kprobes.c 2007-03-31 14:31:24.000000000 +0200
+++ linux-2.6/arch/powerpc/kernel/kprobes.c 2007-03-31 14:35:21.000000000 +0200
@@ -124,22 +124,13 @@ static void __kprobes set_current_kprobe
}

/* Called with kretprobe_lock held */
-void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
- struct kretprobe_instance *ri;
+ ri->ret_addr = (kprobe_opcode_t *)regs->link;

- if ((ri = get_free_rp_inst(rp)) != NULL) {
- ri->rp = rp;
- ri->task = current;
- ri->ret_addr = (kprobe_opcode_t *)regs->link;
-
- /* Replace the return addr with trampoline addr */
- regs->link = (unsigned long)kretprobe_trampoline;
- add_rp_inst(ri);
- } else {
- rp->nmissed++;
- }
+ /* Replace the return addr with trampoline addr */
+ regs->link = (unsigned long)kretprobe_trampoline;
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
Index: linux-2.6/arch/s390/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/arch/s390/kernel/kprobes.c 2007-03-31 14:31:24.000000000 +0200
+++ linux-2.6/arch/s390/kernel/kprobes.c 2007-03-31 14:35:09.000000000 +0200
@@ -271,23 +271,13 @@ static void __kprobes set_current_kprobe
}

/* Called with kretprobe_lock held */
-void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
- struct kretprobe_instance *ri;
+ ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];

- if ((ri = get_free_rp_inst(rp)) != NULL) {
- ri->rp = rp;
- ri->task = current;
- ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];
-
- /* Replace the return addr with trampoline addr */
- regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
-
- add_rp_inst(ri);
- } else {
- rp->nmissed++;
- }
+ /* Replace the return addr with trampoline addr */
+ regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
Index: linux-2.6/arch/x86_64/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/arch/x86_64/kernel/kprobes.c 2007-03-31 14:31:24.000000000 +0200
+++ linux-2.6/arch/x86_64/kernel/kprobes.c 2007-03-31 14:34:46.000000000 +0200
@@ -266,23 +266,14 @@ static void __kprobes prepare_singlestep
}

/* Called with kretprobe_lock held */
-void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
unsigned long *sara = (unsigned long *)regs->rsp;
- struct kretprobe_instance *ri;

- if ((ri = get_free_rp_inst(rp)) != NULL) {
- ri->rp = rp;
- ri->task = current;
- ri->ret_addr = (kprobe_opcode_t *) *sara;
-
- /* Replace the return addr with trampoline addr */
- *sara = (unsigned long) &kretprobe_trampoline;
- add_rp_inst(ri);
- } else {
- rp->nmissed++;
- }
+ ri->ret_addr = (kprobe_opcode_t *) *sara;
+ /* Replace the return addr with trampoline addr */
+ *sara = (unsigned long) &kretprobe_trampoline;
}

int __kprobes kprobe_handler(struct pt_regs *regs)
Index: linux-2.6/include/linux/kprobes.h
===================================================================
--- linux-2.6.orig/include/linux/kprobes.h 2007-03-31 14:36:00.000000000 +0200
+++ linux-2.6/include/linux/kprobes.h 2007-03-31 14:41:13.000000000 +0200
@@ -123,7 +123,8 @@ DECLARE_PER_CPU(struct kprobe *, current
DECLARE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

#ifdef ARCH_SUPPORTS_KRETPROBES
-extern void arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs);
+extern void arch_prepare_kretprobe(struct kretprobe_instance *ri,
+ struct pt_regs *regs);
#else /* ARCH_SUPPORTS_KRETPROBES */
static inline void arch_prepare_kretprobe(struct kretprobe *rp,
struct pt_regs *regs)
@@ -199,8 +200,6 @@ void jprobe_return(void);
int register_kretprobe(struct kretprobe *rp);
void unregister_kretprobe(struct kretprobe *rp);

-struct kretprobe_instance *get_free_rp_inst(struct kretprobe *rp);
-void add_rp_inst(struct kretprobe_instance *ri);
void kprobe_flush_task(struct task_struct *tk);
void recycle_rp_inst(struct kretprobe_instance *ri, struct hlist_head *head);
#else /* CONFIG_KPROBES */
Index: linux-2.6/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/kernel/kprobes.c 2007-03-31 14:26:22.000000000 +0200
+++ linux-2.6/kernel/kprobes.c 2007-03-31 14:46:54.000000000 +0200
@@ -357,46 +357,6 @@ void __kprobes kprobes_inc_nmissed_count
}

/* Called with kretprobe_lock held */
-struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
-{
- struct hlist_node *node;
- struct kretprobe_instance *ri;
- hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
- return ri;
- return NULL;
-}
-
-/* Called with kretprobe_lock held */
-static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
- *rp)
-{
- struct hlist_node *node;
- struct kretprobe_instance *ri;
- hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
- return ri;
- return NULL;
-}
-
-/* Called with kretprobe_lock held */
-void __kprobes add_rp_inst(struct kretprobe_instance *ri)
-{
- /*
- * Remove rp inst off the free list -
- * Add it back when probed function returns
- */
- hlist_del(&ri->uflist);
-
- /* Add rp inst onto table */
- INIT_HLIST_NODE(&ri->hlist);
- hlist_add_head(&ri->hlist,
- &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);
-
- /* Also add this rp inst to the used list. */
- INIT_HLIST_NODE(&ri->uflist);
- hlist_add_head(&ri->uflist, &ri->rp->used_instances);
-}
-
-/* Called with kretprobe_lock held */
void __kprobes recycle_rp_inst(struct kretprobe_instance *ri,
struct hlist_head *head)
{
@@ -449,7 +409,9 @@ void __kprobes kprobe_flush_task(struct
static inline void free_rp_inst(struct kretprobe *rp)
{
struct kretprobe_instance *ri;
- while ((ri = get_free_rp_inst(rp)) != NULL) {
+ struct hlist_node *pos, *next;
+
+ hlist_for_each_entry_safe(ri, pos, next, &rp->free_instances, uflist) {
hlist_del(&ri->uflist);
kfree(ri);
}
@@ -731,7 +693,21 @@ static int __kprobes pre_handler_kretpro

/*TODO: consider to only swap the RA after the last pre_handler fired */
spin_lock_irqsave(&kretprobe_lock, flags);
- arch_prepare_kretprobe(rp, regs);
+ if (!hlist_empty(&rp->free_instances)) {
+ struct kretprobe_instance *ri;
+
+ ri = hlist_entry(rp->free_instances.first,
+ struct kretprobe_instance, uflist);
+ ri->rp = rp;
+ ri->task = current;
+ arch_prepare_kretprobe(ri, regs);
+
+ /* XXX(hch): why is there no hlist_move_head? */
+ hlist_del(&ri->uflist);
+ hlist_add_head(&ri->uflist, &ri->rp->used_instances);
+ hlist_add_head(&ri->hlist, kretprobe_inst_table_head(ri->task));
+ } else
+ rp->nmissed++;
spin_unlock_irqrestore(&kretprobe_lock, flags);
return 0;
}
@@ -794,11 +770,13 @@ void __kprobes unregister_kretprobe(stru
{
unsigned long flags;
struct kretprobe_instance *ri;
+ struct hlist_node *pos, *next;

unregister_kprobe(&rp->kp);
+
/* No race here */
spin_lock_irqsave(&kretprobe_lock, flags);
- while ((ri = get_used_rp_inst(rp)) != NULL) {
+ hlist_for_each_entry_safe(ri, pos, next, &rp->used_instances, uflist) {
ri->rp = NULL;
hlist_del(&ri->uflist);
}
-
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