[RFC][PATCH][take2]kretprobe: kretprobe-booster against 2.6.15-rc5-mm3 for i386

[Masami Hiramatsu <hiramatu at sdl dot hitachi dot co dot jp>]

Hi,

Here is a patch of the kretprobe-booster for i386 arch.
I expect this patch works fine with preemptible kernel.
But it needs more review.

Kretprobe make a target function return to tranpoline code.
With kretprobe-booster, the tranpoline code calls kretprobe's
handler directly instead of causing break interruption.
And tranpoline code returns again to original return address.

This new tranpoline code saves and restores registers, so it
has much compatibility with normal kretprobe.

Best Regards,

-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: hiramatu@sdl.hitachi.co.jp

 kprobes.c |   60 ++++++++++++++++++++++++++++++++++++++++--------------------
 1 files changed, 40 insertions(+), 20 deletions(-)
diff -Narup a/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
--- a/arch/i386/kernel/kprobes.c	2005-12-20 19:55:42.000000000 +0900
+++ b/arch/i386/kernel/kprobes.c	2005-12-20 20:11:47.000000000 +0900
@@ -237,22 +237,53 @@ no_kprobe:
 	return ret;
 }

+static asmlinkage void *__kprobes trampoline_handler(struct pt_regs *regs);
+static void *arch_trampoline_callee;
+
 /*
  * For function-return probes, init_kprobes() establishes a probepoint
  * here. When a retprobed function returns, this probe is hit and
  * trampoline_probe_handler() runs, calling the kretprobe's handler.
  */
- void kretprobe_trampoline_holder(void)
+ void __kprobes kretprobe_trampoline_holder(void)
  {
- 	asm volatile (  ".global kretprobe_trampoline\n"
+	 asm volatile ( ".global kretprobe_trampoline\n"
  			"kretprobe_trampoline: \n"
- 			"nop\n");
- }
+			"	subl $8, %esp\n"
+			"	pushf\n"
+			"	subl $20, %esp\n"
+			"	pushl %eax\n"
+			"	pushl %ebp\n"
+			"	pushl %edi\n"
+			"	pushl %esi\n"
+			"	pushl %edx\n"
+			"	pushl %ecx\n"
+			"	pushl %ebx\n"
+			"	movl %esp, %eax\n"
+			"	pushl %eax\n"
+			"	addl $60, %eax\n"
+			"	movl %eax, 56(%esp)\n"
+			"	movl arch_trampoline_callee, %eax\n"
+			"	call *%eax\n"
+			"	addl $4, %esp\n"
+			"	movl %eax, 56(%esp)\n"
+			"	popl %ebx\n"
+			"	popl %ecx\n"
+			"	popl %edx\n"
+			"	popl %esi\n"
+			"	popl %edi\n"
+			"	popl %ebp\n"
+			"	popl %eax\n"
+			"	addl $20, %esp\n"
+			"	popf\n"
+			"	addl $4, %esp\n"
+			"	ret\n");
+}

 /*
- * Called when we hit the probe point at kretprobe_trampoline
+ * Called from kretprobe_trampoline
  */
-int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
+static asmlinkage void *__kprobes trampoline_handler(struct pt_regs *regs)
 {
         struct kretprobe_instance *ri = NULL;
         struct hlist_head *head;
@@ -297,18 +328,11 @@ int __kprobes trampoline_probe_handler(s
 	}

 	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
-	regs->eip = orig_ret_address;

-	reset_current_kprobe();
 	spin_unlock_irqrestore(&kretprobe_lock, flags);
 	preempt_enable_no_resched();

-	/*
-	 * By returning a non-zero value, we are telling
-	 * kprobe_handler() that we don't want the post_handler
-	 * to run (and have re-enabled preemption)
-	 */
-        return 1;
+	return (void*)orig_ret_address;
 }

 /*
@@ -539,12 +563,8 @@ int __kprobes longjmp_break_handler(stru
 	return 0;
 }

-static struct kprobe trampoline_p = {
-	.addr = (kprobe_opcode_t *) &kretprobe_trampoline,
-	.pre_handler = trampoline_probe_handler
-};
-
 int __init arch_init_kprobes(void)
 {
-	return register_kprobe(&trampoline_p);
+	arch_trampoline_callee= trampoline_handler;
+	return 0;
 }