linux-kernel - [PATCH 2/3] powerpc: kprobes: factor out code to emulate instruction into a helper

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Message-Id: <f7c2116b556de0a764e1c7c5369c13fc9139566b.1487060527.git.naveen.n.rao@linux.vnet.ibm.com>
Date:   Tue, 14 Feb 2017 14:08:02 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 2/3] powerpc: kprobes: factor out code to emulate instruction into a helper

This helper will be used in a subsequent patch to emulate instructions
on re-entering the kprobe handler. No functional change.

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 arch/powerpc/kernel/kprobes.c | 52 ++++++++++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 21 deletions(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index fce05a38851c..9cdf2de31e9e 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -140,6 +140,35 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 	regs->link = (unsigned long)kretprobe_trampoline;
 }
 
+int __kprobes try_to_emulate(struct kprobe *p, struct pt_regs *regs)
+{
+	int ret;
+	unsigned int insn = *p->ainsn.insn;
+
+	/* regs->nip is also adjusted if emulate_step returns 1 */
+	ret = emulate_step(regs, insn);
+	if (ret > 0) {
+		/*
+		 * Once this instruction has been boosted
+		 * successfully, set the boostable flag
+		 */
+		if (unlikely(p->ainsn.boostable == 0))
+			p->ainsn.boostable = 1;
+	} else if (ret < 0) {
+		/*
+		 * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
+		 * So, we should never get here... but, its still
+		 * good to catch them, just in case...
+		 */
+		printk("Can't step on instruction %x\n", insn);
+		BUG();
+	} else if (ret == 0)
+		/* This instruction can't be boosted */
+		p->ainsn.boostable = -1;
+
+	return ret;
+}
+
 int __kprobes kprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe *p;
@@ -235,18 +264,9 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
 
 ss_probe:
 	if (p->ainsn.boostable >= 0) {
-		unsigned int insn = *p->ainsn.insn;
+		ret = try_to_emulate(p, regs);
 
-		/* regs->nip is also adjusted if emulate_step returns 1 */
-		ret = emulate_step(regs, insn);
 		if (ret > 0) {
-			/*
-			 * Once this instruction has been boosted
-			 * successfully, set the boostable flag
-			 */
-			if (unlikely(p->ainsn.boostable == 0))
-				p->ainsn.boostable = 1;
-
 			if (p->post_handler)
 				p->post_handler(p, regs, 0);
 
@@ -254,17 +274,7 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
 			reset_current_kprobe();
 			preempt_enable_no_resched();
 			return 1;
-		} else if (ret < 0) {
-			/*
-			 * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
-			 * So, we should never get here... but, its still
-			 * good to catch them, just in case...
-			 */
-			printk("Can't step on instruction %x\n", insn);
-			BUG();
-		} else if (ret == 0)
-			/* This instruction can't be boosted */
-			p->ainsn.boostable = -1;
+		}
 	}
 	prepare_singlestep(p, regs);
 	kcb->kprobe_status = KPROBE_HIT_SS;
-- 
2.11.0