Message-ID: <20070925100053.GA16731@in.ibm.com>
Date:	Tue, 25 Sep 2007 15:30:53 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	lkml <linux-kernel@...r.kernel.org>, prasanna@...ibm.com,
	anil.s.keshavamurthy@...el.com, mathieu.desnoyers@...ymtl.ca,
	akpm <akpm@...ux-foundation.org>, sam@...nborg.org,
	davem@...emloft.net
Subject: Re: [PATCH/RFC] samples/: move kprobes sources to samples

On Tue, Sep 25, 2007 at 09:57:11AM +0100, Christoph Hellwig wrote:
> On Tue, Sep 25, 2007 at 02:13:33PM +0530, Ananth N Mavinakayanahalli wrote:
> > +++ linux-2.6.23-rc7/samples/kprobes/jprobe_example.c
> > @@ -0,0 +1,69 @@
> > +/*jprobe-example.c */
> 
> I don't think we should have this type of comment in any of the files.
> 
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/fs.h>
> > +#include <linux/uio.h>
> 
> I don't think you'll need uio,h here.

Fixed. Actually, we don't need the fs.h either... I've audited and
cleaned up the other examples also.

> > + * Jumper probe for do_fork.
> > + * Mirror principle enables access to arguments of the probed routine
> > + * from the probe handler.
> > + */
> > +static const char *probed_func = "do_fork";
> > +
> 
> > +	/* Always end with a call to jprobe_return(). */
> > +	jprobe_return();
> > +
> > +	/*NOTREACHED*/
> > +	return 0;
> 
> I'd rather write this as:
> 
> 	/* Always end with a call to jprobe_return(). */
> 	jprobe_return();
> 	return 0;
> }

Fixed

> Also a a note not to these example but general kprobes code I've
> bee wondering whether jprobe_return() should just include the return.
> Yes, macros including a return are ugly, but in this case jprobe_return
> actually handles the return anyway through deep magic.

Right; but the issue here is that in jprobe_return() we don't know what
the jprobed function would return. Also, we've left this the way it
is just so the compiler is happy. (And jprobe_return() is a function
with each arch doing its own magic :-))

> > +static struct jprobe my_jprobe = {
> > +	.entry = jdo_fork
> > +};
> > +
> > +static int __init jprobe_init(void)
> > +{
> > +	int ret;
> > +	my_jprobe.kp.symbol_name = (char *)probed_func;
> 
> Shouldn't this be simply done in the static initialization, ala:
> 
> static struct jprobe my_jprobe = {
> 	.entry			= jdo_fork,
> 	.kp = {
> 		.symbol_name	= "do_fork",
> 	},
> };
> 
> (same for the other examples)

Agreed. Fixed.

> > +static int handler_pre(struct kprobe *p, struct pt_regs *regs)
> > +{
> > +#ifdef CONFIG_X86_32
> > +	printk("pre_handler: p->addr = 0x%p, eip = %lx, eflags = 0x%lx\n",
> > +		p->addr, regs->eip, regs->eflags);
> > +#endif
> > +#ifdef CONFIG_X86_64
> > +	printk("pre_handler: p->addr = 0x%p, rip = %lx, eflags = 0x%lx\n",
> > +		p->addr, regs->rip, regs->eflags);
> > +#endif
> > +#ifdef CONFIG_PPC
> > +	printk("pre_handler: p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n",
> > +		p->addr, regs->nip, regs->msr);
> > +#endif
> 
> Now this is really ugly.  We should really have macros for the interesting
> registers (instruction pointer, frame pointer, stack pointer) in kdebug.h.
> systemtap runtime already has them for supported architectures, any care
> to port them over?
> 
> (note that this is not an objection to the patch as-is, but rather a
>  suggestion for later improvement of the whole thing)

Agreed
 
> Thanks a lot for moving this in the right place!

Updated patch...

Thanks Randy for kicking this off. I've updated kprobe_example.c to work
on powerpc also. In addition I have:

o Removed samples/Kbuild so the build goes on fine
o Modified examples slightly to display output better (cosmetic)
o Changed the kretprobe_example.c to probe do_fork and log the new pid
o Fixed code per roel's nitpicks
o Renamed kretprobe-example.c to kretprobe_example.c for consistancy
o Made changes suggested by Christoph
o Cleaned up unneeded #includes


Signed-off-by: Randy Dunlap <randy.dunlap@...cle.com>
Signed-off-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>
---
 Documentation/kprobes.txt           |  214 ------------------------------------
 samples/Kbuild                      |    2 
 samples/Kconfig                     |    5 
 samples/Makefile                    |    3 
 samples/kprobes/Makefile            |    5 
 samples/kprobes/jprobe_example.c    |   64 ++++++++++
 samples/kprobes/kprobe_example.c    |   89 ++++++++++++++
 samples/kprobes/kretprobe_example.c |   59 +++++++++
 8 files changed, 230 insertions(+), 211 deletions(-)

Index: linux-2.6.23-rc7/samples/kprobes/Makefile
===================================================================
--- /dev/null
+++ linux-2.6.23-rc7/samples/kprobes/Makefile
@@ -0,0 +1,5 @@
+# builds the kprobes example kernel modules;
+# then to use one (as root):  insmod <module_name.ko>
+
+obj-$(CONFIG_SAMPLE_KPROBES) += kprobe_example.o jprobe_example.o \
+		kretprobe_example.o
Index: linux-2.6.23-rc7/samples/Kconfig
===================================================================
--- linux-2.6.23-rc7.orig/samples/Kconfig
+++ linux-2.6.23-rc7/samples/Kconfig
@@ -7,5 +7,10 @@ menuconfig SAMPLES
 
 if SAMPLES
 
+config SAMPLE_KPROBES
+	tristate "Build kprobes examples -- loadable modules only"
+	depends on KPROBES && m
+	help
+	  This builds several kprobes example modules.
 
 endif # SAMPLES
Index: linux-2.6.23-rc7/samples/kprobes/jprobe_example.c
===================================================================
--- /dev/null
+++ linux-2.6.23-rc7/samples/kprobes/jprobe_example.c
@@ -0,0 +1,64 @@
+/*
+ * Here's a sample kernel module showing the use of jprobes to dump
+ * the arguments of do_fork().
+ *
+ * Build and insert the kernel module as done in the kprobe example.
+ * You will see the trace data in /var/log/messages and on the
+ * console whenever do_fork() is invoked to create a new process.
+ * (Some messages may be suppressed if syslogd is configured to
+ * eliminate duplicate messages.)
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+
+/*
+ * Jumper probe for do_fork.
+ * Mirror principle enables access to arguments of the probed routine
+ * from the probe handler.
+ */
+
+/* Proxy routine having the same arguments as actual do_fork() routine */
+static long jdo_fork(unsigned long clone_flags, unsigned long stack_start,
+	      struct pt_regs *regs, unsigned long stack_size,
+	      int __user * parent_tidptr, int __user * child_tidptr)
+{
+	printk("jprobe: clone_flags = 0x%lx, stack_size = 0x%lx, regs = 0x%p\n",
+	       clone_flags, stack_size, regs);
+
+	/* Always end with a call to jprobe_return(). */
+	jprobe_return();
+	return 0;
+}
+
+static struct jprobe my_jprobe = {
+	.entry			= jdo_fork,
+	.kp = {
+		.symbol_name	= "do_fork",
+	},
+};
+
+static int __init jprobe_init(void)
+{
+	int ret;
+
+	ret = register_jprobe(&my_jprobe);
+	if (ret < 0) {
+		printk("register_jprobe failed, returned %d\n", ret);
+		return -1;
+	}
+	printk("Planted jprobe at %p, handler addr %p\n",
+	       my_jprobe.kp.addr, my_jprobe.entry);
+	return 0;
+}
+
+static void __exit jprobe_exit(void)
+{
+	unregister_jprobe(&my_jprobe);
+	printk("jprobe at %p unregistered\n", my_jprobe.kp.addr);
+}
+
+module_init(jprobe_init)
+module_exit(jprobe_exit)
+MODULE_LICENSE("GPL");
Index: linux-2.6.23-rc7/samples/kprobes/kprobe_example.c
===================================================================
--- /dev/null
+++ linux-2.6.23-rc7/samples/kprobes/kprobe_example.c
@@ -0,0 +1,89 @@
+/*
+ * NOTE: This example is works on x86 and powerpc.
+ * Here's a sample kernel module showing the use of kprobes to dump a
+ * stack trace and selected registers when do_fork() is called.
+ *
+ * You will see the trace data in /var/log/messages and on the console
+ * whenever do_fork() is invoked to create a new process.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+
+/* For each probe you need to allocate a kprobe structure */
+static struct kprobe kp = {
+	.symbol_name	= "do_fork",
+};
+
+/* kprobe pre_handler: called just before the probed instruction is executed */
+static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+#ifdef CONFIG_X86_32
+	printk("pre_handler: p->addr = 0x%p, eip = %lx, eflags = 0x%lx\n",
+		p->addr, regs->eip, regs->eflags);
+#endif
+#ifdef CONFIG_X86_64
+	printk("pre_handler: p->addr = 0x%p, rip = %lx, eflags = 0x%lx\n",
+		p->addr, regs->rip, regs->eflags);
+#endif
+#ifdef CONFIG_PPC
+	printk("pre_handler: p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n",
+		p->addr, regs->nip, regs->msr);
+#endif
+
+	/* A dump_stack() here will give a stack backtrace */
+	return 0;
+}
+
+/* kprobe post_handler: called after the probed instruction is executed */
+static void handler_post(struct kprobe *p, struct pt_regs *regs, unsigned long flags)
+{
+#if defined(CONFIG_X86_32) || defined(CONFIG_X86_64)
+	printk("post_handler: p->addr = 0x%p, eflags = 0x%lx\n",
+		p->addr, regs->eflags);
+#endif
+#ifdef CONFIG_PPC
+	printk("post_handler: p->addr = 0x%p, msr = 0x%lx\n",
+		p->addr, regs->msr);
+#endif
+}
+
+/*
+ * fault_handler: this is called if an exception is generated for any
+ * instruction within the pre- or post-handler, or when Kprobes
+ * single-steps the probed instruction.
+ */
+static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
+{
+	printk("fault_handler: p->addr = 0x%p, trap #%dn",
+		p->addr, trapnr);
+	/* Return 0 because we don't handle the fault. */
+	return 0;
+}
+
+static int __init kprobe_init(void)
+{
+	int ret;
+	kp.pre_handler = handler_pre;
+	kp.post_handler = handler_post;
+	kp.fault_handler = handler_fault;
+
+	ret = register_kprobe(&kp);
+	if (ret < 0) {
+		printk("register_kprobe failed, returned %d\n", ret);
+		return ret;
+	}
+	printk("Planted kprobe at %p\n", kp.addr);
+	return 0;
+}
+
+static void __exit kprobe_exit(void)
+{
+	unregister_kprobe(&kp);
+	printk("kprobe at %p unregistered\n", kp.addr);
+}
+
+module_init(kprobe_init)
+module_exit(kprobe_exit)
+MODULE_LICENSE("GPL");
Index: linux-2.6.23-rc7/samples/kprobes/kretprobe_example.c
===================================================================
--- /dev/null
+++ linux-2.6.23-rc7/samples/kprobes/kretprobe_example.c
@@ -0,0 +1,59 @@
+/*
+ * Here's a sample kernel module showing the use of return probes to
+ * report the return value from do_fork().
+ *
+ * Build and insert the kernel module as done in the kprobe example.
+ * You will see the trace data in /var/log/messages and on the console
+ * whenever sys_open() returns a negative value.  (Some messages
+ * may be suppressed if syslogd is configured to eliminate duplicate
+ * messages.)
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+
+/* Return-probe handler: If the probed function fails, log the return value. */
+static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+	int retval = regs_return_value(regs);
+
+	printk("do_fork returns %d\n", retval);
+	return 0;
+}
+
+static struct kretprobe my_kretprobe = {
+	.handler		= ret_handler,
+	.kp = {
+		.symbol_name	= "do_fork",
+	},
+	/* Probe up to 20 instances concurrently. */
+	.maxactive		= 20,
+};
+
+static int __init kretprobe_init(void)
+{
+	int ret;
+
+	ret = register_kretprobe(&my_kretprobe);
+	if (ret < 0) {
+		printk("register_kretprobe failed, returned %d\n", ret);
+		return -1;
+	}
+	printk("Planted return probe at %p\n", my_kretprobe.kp.addr);
+	return 0;
+}
+
+static void __exit kretprobe_exit(void)
+{
+	unregister_kretprobe(&my_kretprobe);
+	printk("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);
+
+	/* nmissed > 0 suggests that maxactive was set too low. */
+	printk("Missed probing %d instances of do_fork()\n",
+		my_kretprobe.nmissed);
+}
+
+module_init(kretprobe_init)
+module_exit(kretprobe_exit)
+MODULE_LICENSE("GPL");
Index: linux-2.6.23-rc7/Documentation/kprobes.txt
===================================================================
--- linux-2.6.23-rc7.orig/Documentation/kprobes.txt
+++ linux-2.6.23-rc7/Documentation/kprobes.txt
@@ -166,7 +166,8 @@ code mapping.
 The Kprobes API includes a "register" function and an "unregister"
 function for each type of probe.  Here are terse, mini-man-page
 specifications for these functions and the associated probe handlers
-that you'll write.  See the latter half of this document for examples.
+that you'll write.  See the files in the samples/kprobes/ sub-directory
+for examples.
 
 4.1 register_kprobe
 
@@ -392,220 +393,15 @@ e. Watchpoint probes (which fire on data
 
 8. Kprobes Example
 
-Here's a sample kernel module showing the use of kprobes to dump a
-stack trace and selected i386 registers when do_fork() is called.
------ cut here -----
-/*kprobe_example.c*/
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/kprobes.h>
-#include <linux/sched.h>
-
-/*For each probe you need to allocate a kprobe structure*/
-static struct kprobe kp;
-
-/*kprobe pre_handler: called just before the probed instruction is executed*/
-int handler_pre(struct kprobe *p, struct pt_regs *regs)
-{
-	printk("pre_handler: p->addr=0x%p, eip=%lx, eflags=0x%lx\n",
-		p->addr, regs->eip, regs->eflags);
-	dump_stack();
-	return 0;
-}
-
-/*kprobe post_handler: called after the probed instruction is executed*/
-void handler_post(struct kprobe *p, struct pt_regs *regs, unsigned long flags)
-{
-	printk("post_handler: p->addr=0x%p, eflags=0x%lx\n",
-		p->addr, regs->eflags);
-}
-
-/* fault_handler: this is called if an exception is generated for any
- * instruction within the pre- or post-handler, or when Kprobes
- * single-steps the probed instruction.
- */
-int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
-{
-	printk("fault_handler: p->addr=0x%p, trap #%dn",
-		p->addr, trapnr);
-	/* Return 0 because we don't handle the fault. */
-	return 0;
-}
-
-static int __init kprobe_init(void)
-{
-	int ret;
-	kp.pre_handler = handler_pre;
-	kp.post_handler = handler_post;
-	kp.fault_handler = handler_fault;
-	kp.symbol_name = "do_fork";
-
-	ret = register_kprobe(&kp);
-	if (ret < 0) {
-		printk("register_kprobe failed, returned %d\n", ret);
-		return ret;
-	}
-	printk("kprobe registered\n");
-	return 0;
-}
-
-static void __exit kprobe_exit(void)
-{
-	unregister_kprobe(&kp);
-	printk("kprobe unregistered\n");
-}
-
-module_init(kprobe_init)
-module_exit(kprobe_exit)
-MODULE_LICENSE("GPL");
------ cut here -----
-
-You can build the kernel module, kprobe-example.ko, using the following
-Makefile:
------ cut here -----
-obj-m := kprobe-example.o
-KDIR := /lib/modules/$(shell uname -r)/build
-PWD := $(shell pwd)
-default:
-	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
-clean:
-	rm -f *.mod.c *.ko *.o
------ cut here -----
-
-$ make
-$ su -
-...
-# insmod kprobe-example.ko
-
-You will see the trace data in /var/log/messages and on the console
-whenever do_fork() is invoked to create a new process.
+See samples/kprobes/kprobe_example.c.
 
 9. Jprobes Example
 
-Here's a sample kernel module showing the use of jprobes to dump
-the arguments of do_fork().
------ cut here -----
-/*jprobe-example.c */
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/fs.h>
-#include <linux/uio.h>
-#include <linux/kprobes.h>
-
-/*
- * Jumper probe for do_fork.
- * Mirror principle enables access to arguments of the probed routine
- * from the probe handler.
- */
-
-/* Proxy routine having the same arguments as actual do_fork() routine */
-long jdo_fork(unsigned long clone_flags, unsigned long stack_start,
-	      struct pt_regs *regs, unsigned long stack_size,
-	      int __user * parent_tidptr, int __user * child_tidptr)
-{
-	printk("jprobe: clone_flags=0x%lx, stack_size=0x%lx, regs=0x%p\n",
-	       clone_flags, stack_size, regs);
-	/* Always end with a call to jprobe_return(). */
-	jprobe_return();
-	/*NOTREACHED*/
-	return 0;
-}
-
-static struct jprobe my_jprobe = {
-	.entry = jdo_fork
-};
-
-static int __init jprobe_init(void)
-{
-	int ret;
-	my_jprobe.kp.symbol_name = "do_fork";
-
-	if ((ret = register_jprobe(&my_jprobe)) <0) {
-		printk("register_jprobe failed, returned %d\n", ret);
-		return -1;
-	}
-	printk("Planted jprobe at %p, handler addr %p\n",
-	       my_jprobe.kp.addr, my_jprobe.entry);
-	return 0;
-}
-
-static void __exit jprobe_exit(void)
-{
-	unregister_jprobe(&my_jprobe);
-	printk("jprobe unregistered\n");
-}
-
-module_init(jprobe_init)
-module_exit(jprobe_exit)
-MODULE_LICENSE("GPL");
------ cut here -----
-
-Build and insert the kernel module as shown in the above kprobe
-example.  You will see the trace data in /var/log/messages and on
-the console whenever do_fork() is invoked to create a new process.
-(Some messages may be suppressed if syslogd is configured to
-eliminate duplicate messages.)
+See samples/kprobes/jprobe_example.c.
 
 10. Kretprobes Example
 
-Here's a sample kernel module showing the use of return probes to
-report failed calls to sys_open().
------ cut here -----
-/*kretprobe-example.c*/
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/kprobes.h>
-
-static const char *probed_func = "sys_open";
-
-/* Return-probe handler: If the probed function fails, log the return value. */
-static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
-{
-	int retval = regs_return_value(regs);
-	if (retval < 0) {
-		printk("%s returns %d\n", probed_func, retval);
-	}
-	return 0;
-}
-
-static struct kretprobe my_kretprobe = {
-	.handler = ret_handler,
-	/* Probe up to 20 instances concurrently. */
-	.maxactive = 20
-};
-
-static int __init kretprobe_init(void)
-{
-	int ret;
-	my_kretprobe.kp.symbol_name = (char *)probed_func;
-
-	if ((ret = register_kretprobe(&my_kretprobe)) < 0) {
-		printk("register_kretprobe failed, returned %d\n", ret);
-		return -1;
-	}
-	printk("Planted return probe at %p\n", my_kretprobe.kp.addr);
-	return 0;
-}
-
-static void __exit kretprobe_exit(void)
-{
-	unregister_kretprobe(&my_kretprobe);
-	printk("kretprobe unregistered\n");
-	/* nmissed > 0 suggests that maxactive was set too low. */
-	printk("Missed probing %d instances of %s\n",
-		my_kretprobe.nmissed, probed_func);
-}
-
-module_init(kretprobe_init)
-module_exit(kretprobe_exit)
-MODULE_LICENSE("GPL");
------ cut here -----
-
-Build and insert the kernel module as shown in the above kprobe
-example.  You will see the trace data in /var/log/messages and on the
-console whenever sys_open() returns a negative value.  (Some messages
-may be suppressed if syslogd is configured to eliminate duplicate
-messages.)
+See samples/kprobes/kretprobe_example.c.
 
 For additional information on Kprobes, refer to the following URLs:
 http://www-106.ibm.com/developerworks/library/l-kprobes.html?ca=dgr-lnxw42Kprobe
Index: linux-2.6.23-rc7/samples/Makefile
===================================================================
--- /dev/null
+++ linux-2.6.23-rc7/samples/Makefile
@@ -0,0 +1,3 @@
+# Makefile for Linux samples code
+
+obj-$(CONFIG_SAMPLES) += kprobes/
Index: linux-2.6.23-rc7/samples/Kbuild
===================================================================
--- linux-2.6.23-rc7.orig/samples/Kbuild
+++ /dev/null
@@ -1,2 +0,0 @@
-# Makefile for Linux samples code
-
-
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