linux-kernel - [PATCH] Subject: kprobes-x86: correct post-eip value in post

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Date:	Sun, 16 Mar 2008 03:21:21 -0500
From:	"Yakov Lerner" <iler.ml@...il.com>
To:	prasanna@...ibm.com, ananth@...ibm.com,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org, iler.ml@...il.com
Subject: [PATCH] Subject: kprobes-x86: correct post-eip value in post_hander()

I was trying to get the address of instruction to be executed 
next after the kprobed instruction.  But regs->eip in post_handler()
contains value which is useless to the user. It's pre-corrected value.
This value is difficult to use without access to resume_execution(), which
is not exported anyway.
I moved the invocation of post_handler() to *after* resume_execution().
Now regs->eip contains meaningful value in post_handler().

I do not think this change breaks any backward-compatibility.
To make meaning of the old value, post_handler() would need access to
resume_execution() which is not exported.  I have difficulty to believe
that previous, uncorrected, regs->eip can be meaningfully used in
post_handler().

Signed-off-by: Yakov Lerner <iler.ml@...il.com>
---
 arch/x86/kernel/kprobes.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 34a5912..60392e2 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -858,15 +858,15 @@ static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 	if (!cur)
 		return 0;

+	resume_execution(cur, regs, kcb);
+	regs->flags |= kcb->kprobe_saved_flags;
+	trace_hardirqs_fixup_flags(regs->flags);
+
 	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 		kcb->kprobe_status = KPROBE_HIT_SSDONE;
 		cur->post_handler(cur, regs, 0);
 	}

-	resume_execution(cur, regs, kcb);
-	regs->flags |= kcb->kprobe_saved_flags;
-	trace_hardirqs_fixup_flags(regs->flags);
-
 	/* Restore back the original saved kprobes variables and continue. */
 	if (kcb->kprobe_status == KPROBE_REENTER) {
 		restore_previous_kprobe(kcb);
-- 
1.5.4.4

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