linux-kernel - Re: [PATCH] SAMPLES: kprobe_example: make it more easy to use

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Message-ID: <CAM2zO=Csp3EvEQKoxZuKJzdWbsCexV-YYjxoaUefYSHawRmEDA@mail.gmail.com>
Date:	Tue, 5 Jul 2011 10:00:29 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	ananth@...ibm.com
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] SAMPLES: kprobe_example: make it more easy to use

On Mon, Jul 4, 2011 at 6:14 PM, Ananth N Mavinakayanahalli
<ananth@...ibm.com> wrote:
> On Mon, Jul 04, 2011 at 03:27:39PM +0800, Yong Zhang wrote:
>> From: Yong Zhang <yong.zhang0@...il.com>
>> Subject: [PATCH] SAMPLES: kprobe_example: make it more easy to use
>
> ...
>
>> -     printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\n",
>> -             p->addr, regs->flags);
>> +     printk(KERN_INFO "post_handler: p->addr = 0x%p, ip = %lx,"
>> +                     " flags = 0x%lx\n",
>> +             p->addr, regs->ip, regs->flags);
>
> You are probably better off using the instruction_pointer(regs) helper
> here and elsewhere..

Ah, good to know this wrapper :)

Updated like below:
---
From: Yong Zhang <yong.zhang0@...il.com>
Subject: [PATCH V2] SAMPLES: kprobe_example: make it more easy to use

Add parameter 'func' and 'offset' to it, thus make it more easy
to kprobe certain offset/function.

Also print the next PC in post_handler(), thus we can ealily
tell if there is something is wrong when kprobe fails. This
is inspirited by a bug which explores an issue on POWERPC-32
when intruction is emulated: https://lkml.org/lkml/2011/6/24/53

Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
---
Changes from V1:
  Using wrapper function instruction_pointer() to get next PC.

 samples/kprobes/kprobe_example.c |   37 +++++++++++++++++++++++++------------
 1 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c
index ebf5e0c..8394e98 100644
--- a/samples/kprobes/kprobe_example.c
+++ b/samples/kprobes/kprobe_example.c
@@ -13,11 +13,18 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/kprobes.h>
+#include <linux/limits.h>
+
+static char func_name[NAME_MAX] = "do_fork";
+module_param_string(func, func_name, NAME_MAX, S_IRUGO);
+MODULE_PARM_DESC(func, "Function to kprobe");
+
+static unsigned int offset;
+module_param(offset, uint, S_IRUGO);
+MODULE_PARM_DESC(offset, "Function offset to kprobe");

 /* For each probe you need to allocate a kprobe structure */
-static struct kprobe kp = {
-	.symbol_name	= "do_fork",
-};
+static struct kprobe kp;

 /* kprobe pre_handler: called just before the probed instruction is executed */
 static int handler_pre(struct kprobe *p, struct pt_regs *regs)
@@ -25,17 +32,17 @@ static int handler_pre(struct kprobe *p, struct
pt_regs *regs)
 #ifdef CONFIG_X86
 	printk(KERN_INFO "pre_handler: p->addr = 0x%p, ip = %lx,"
 			" flags = 0x%lx\n",
-		p->addr, regs->ip, regs->flags);
+		p->addr, instruction_pointer(regs), regs->flags);
 #endif
 #ifdef CONFIG_PPC
 	printk(KERN_INFO "pre_handler: p->addr = 0x%p, nip = 0x%lx,"
 			" msr = 0x%lx\n",
-		p->addr, regs->nip, regs->msr);
+		p->addr, instruction_pointer(regs), regs->msr);
 #endif
 #ifdef CONFIG_MIPS
 	printk(KERN_INFO "pre_handler: p->addr = 0x%p, epc = 0x%lx,"
 			" status = 0x%lx\n",
-		p->addr, regs->cp0_epc, regs->cp0_status);
+		p->addr, instruction_pointer(regs), regs->cp0_status);
 #endif

 	/* A dump_stack() here will give a stack backtrace */
@@ -47,16 +54,20 @@ static void handler_post(struct kprobe *p, struct
pt_regs *regs,
 				unsigned long flags)
 {
 #ifdef CONFIG_X86
-	printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\n",
-		p->addr, regs->flags);
+	printk(KERN_INFO "post_handler: p->addr = 0x%p, ip = %lx,"
+			" flags = 0x%lx\n",
+		p->addr, instruction_pointer(regs), regs->flags);
 #endif
 #ifdef CONFIG_PPC
-	printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\n",
-		p->addr, regs->msr);
+	printk(KERN_INFO "post_handler: p->addr = 0x%p, nip = 0x%lx,"
+			" msr = 0x%lx\n",
+		p->addr, instruction_pointer(regs), regs->msr);
+	dump_stack();
 #endif
 #ifdef CONFIG_MIPS
-	printk(KERN_INFO "post_handler: p->addr = 0x%p, status = 0x%lx\n",
-		p->addr, regs->cp0_status);
+	printk(KERN_INFO "post_handler: p->addr = 0x%p, epc = 0x%lx,"
+			" status = 0x%lx\n",
+		p->addr, instruction_pointer(regs), regs->cp0_status);
 #endif
 }

@@ -76,6 +87,8 @@ static int handler_fault(struct kprobe *p, struct
pt_regs *regs, int trapnr)
 static int __init kprobe_init(void)
 {
 	int ret;
+	kp.symbol_name = func_name;
+	kp.offset = offset;
 	kp.pre_handler = handler_pre;
 	kp.post_handler = handler_post;
 	kp.fault_handler = handler_fault;
-- 
1.7.4.1

View attachment "0001-SAMPLES-kprobe_example-make-it-more-easy-to-use.patch" of type "text/x-patch" (3639 bytes)