Message-ID: <20090320003533.GB6895@nowhere>
Date:	Fri, 20 Mar 2009 01:35:33 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: [RFC][PATCH -tip 1/9] tracing: kprobe-tracer plugin core

On Thu, Mar 19, 2009 at 05:10:02PM -0400, Masami Hiramatsu wrote:
> Add kprobes based event tracer on ftrace.
> 
> This tracer is similar to the events tracer which is based on Tracepoint
> infrastructure. Instead of Tracepoint, this tracer is based on kprobes(kprobe
> and kretprobe). It probes anywhere where kprobes can probe(this means, all
> functions body except for __kprobes functions).
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> ---
>  Documentation/ftrace.txt    |   55 ++++++
>  kernel/trace/Kconfig        |    9 +
>  kernel/trace/Makefile       |    1 +
>  kernel/trace/trace_kprobe.c |  410 +++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 475 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/ftrace.txt b/Documentation/ftrace.txt
> index fd9a3e6..a957adf 100644
> --- a/Documentation/ftrace.txt
> +++ b/Documentation/ftrace.txt
> @@ -1310,6 +1310,61 @@ dereference in a kernel module:
>  [...]
> 
> 
> +kprobe-based event tracer
> +---------------------------
> +
> +This tracer is similar to the events tracer which is based on Tracepoint
> +infrastructure. Instead of Tracepoint, this tracer is based on kprobes(kprobe
> +and kretprobe). It probes anywhere where kprobes can probe(this means, all
> +functions body except for __kprobes functions).
> +
> +Unlike the function tracer, this tracer can probe instructions inside of
> +kernel functions. It allows you to check which instruction has been executed.
> +
> +Unlike the Tracepoint based events tracer, this tracer can add new probe points
> +on the fly.
> +
> +Similar to the events tracer, this tracer doesn't need to be activated via
> +current_tracer, instead of that, just set probe points via
> +/debug/tracing/kprobe_probes.
> +
> +Synopsis of kprobe_probes:
> +  p SYMBOL[+offs|-offs]|MEMADDR	: set a probe
> +  r SYMBOL[+0]				: set a return probe
> +
> +E.g.
> +  echo p sys_open > /debug/tracing/kprobe_probes
> +
> + This sets a kprobe on the top of sys_open() function.
> +
> +  echo r sys_open >> /debug/tracing/kprobe_probes
> +
> + This sets a kretprobe on the return point of sys_open() function.
> +
> +  echo > /debug/tracing/kprobe_probes
> +
> + This clears all probe points. and you can see the traced information via
> +/debug/tracing/trace.
> +
> +  echo /debug/tracing/trace
> +# tracer: nop
> +#
> +#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> +#              | |       |          |         |
> +           <...>-5117  [003]   416.481638: sys_open: @sys_open+0
> +           <...>-5117  [003]   416.481662: syscall_call: <-sys_open+0
> +           <...>-5117  [003]   416.481739: sys_open: @sys_open+0
> +           <...>-5117  [003]   416.481762: sysenter_do_call: <-sys_open+0
> +           <...>-5117  [003]   416.481818: sys_open: @sys_open+0
> +           <...>-5117  [003]   416.481842: sysenter_do_call: <-sys_open+0
> +           <...>-5117  [003]   416.481882: sys_open: @sys_open+0
> +           <...>-5117  [003]   416.481905: sysenter_do_call: <-sys_open+0
> +
> + @SYMBOL means that kernel hits a probe, and <-SYMBOL means kernel returns
> +from SYMBOL(e.g. "sysenter_do_call: <-sys_open+0" means kernel returns from
> +sys_open to sysenter_do_call).
> +
> +
>  function graph tracer
>  ---------------------------
> 
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index b0a46f8..1980703 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -353,6 +353,15 @@ config BLK_DEV_IO_TRACE
> 
>  	  If unsure, say N.
> 
> +config KPROBE_TRACER
> +	depends on KPROBES
> +	depends on X86
> +	bool "Trace kprobes"
> +	select TRACING
> +	help
> +	  This tracer probes everywhere where kprobes can probe it, and
> +	  records various registers and memories specified by user.
> +
>  config DYNAMIC_FTRACE
>  	bool "enable/disable ftrace tracepoints dynamically"
>  	depends on FUNCTION_TRACER
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index c3feea0..3b8de70 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -44,5 +44,6 @@ obj-$(CONFIG_EVENT_TRACER) += trace_events.o
>  obj-$(CONFIG_EVENT_TRACER) += events.o
>  obj-$(CONFIG_EVENT_TRACER) += trace_export.o
>  obj-$(CONFIG_FTRACE_SYSCALLS) += trace_syscalls.o
> +obj-$(CONFIG_KPROBE_TRACER) += trace_kprobe.o
> 
>  libftrace-y := ftrace.o
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> new file mode 100644
> index 0000000..33bb355
> --- /dev/null
> +++ b/kernel/trace/trace_kprobe.c
> @@ -0,0 +1,410 @@
> +/*
> + * kprobe based kernel tracer
> + *
> + * Created by Masami Hiramatsu <mhiramat@...hat.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
> + */
> +
> +#include <linux/module.h>
> +#include <linux/uaccess.h>
> +#include <linux/kprobes.h>
> +#include <linux/seq_file.h>
> +#include <linux/slab.h>
> +#include <linux/smp.h>
> +#include <linux/debugfs.h>
> +#include <linux/types.h>
> +#include <linux/string.h>
> +#include <linux/ctype.h>
> +
> +#include <linux/ftrace.h>
> +#include "trace.h"
> +
> +/**
> + * kprobe_trace_core
> + */
> +#define TRACE_MAXARGS 6
> +
> +struct trace_probe {
> +	struct list_head	list;
> +	union {
> +		struct kprobe		kp;
> +		struct kretprobe	rp;
> +	};
> +	const char		*symbol;	/* symbol name */
> +};
> +
> +static void kprobe_trace_record(unsigned long ip, struct trace_probe *tp,
> +				struct pt_regs *regs);
> +
> +static int kprobe_trace_func(struct kprobe *kp, struct pt_regs *regs)
> +{
> +	struct trace_probe *tp = container_of(kp, struct trace_probe, kp);
> +
> +	kprobe_trace_record(instruction_pointer(regs), tp, regs);
> +	return 0;
> +}
> +
> +static int kretprobe_trace_func(struct kretprobe_instance *ri,
> +				struct pt_regs *regs)
> +{
> +	struct trace_probe *tp = container_of(ri->rp, struct trace_probe, rp);
> +
> +	kprobe_trace_record((unsigned long)ri->ret_addr, tp, regs);
> +	return 0;
> +}
> +
> +static int probe_is_return(struct trace_probe *tp)
> +{
> +	return (tp->rp.handler == kretprobe_trace_func);
> +}
> +
> +static const char *probe_symbol(struct trace_probe *tp)
> +{
> +	return tp->symbol ? tp->symbol : "unknown";
> +}
> +
> +static long probe_offset(struct trace_probe *tp)
> +{
> +	return (probe_is_return(tp)) ? tp->rp.kp.offset : tp->kp.offset;
> +}
> +
> +static void *probe_address(struct trace_probe *tp)
> +{
> +	return (probe_is_return(tp)) ? tp->rp.kp.addr : tp->kp.addr;
> +}
> +
> +
> +static DEFINE_MUTEX(probe_lock);
> +static LIST_HEAD(probe_list);
> +
> +static struct trace_probe *alloc_trace_probe(const char *symbol)
> +{
> +	struct trace_probe *tp;
> +
> +	tp = kzalloc(sizeof(struct trace_probe), GFP_KERNEL);
> +	if (!tp)
> +		return ERR_PTR(-ENOMEM);
> +
> +	if (symbol) {
> +		tp->symbol = kstrdup(symbol, GFP_KERNEL);
> +		if (!tp->symbol) {
> +			kfree(tp);
> +			return ERR_PTR(-ENOMEM);
> +		}
> +	}
> +
> +	INIT_LIST_HEAD(&tp->list);
> +	return tp;
> +}
> +
> +static void free_trace_probe(struct trace_probe *tp)
> +{
> +	kfree(tp->symbol);
> +	kfree(tp);
> +}
> +
> +static int register_trace_probe(struct trace_probe *tp)
> +{
> +	int ret;
> +
> +	mutex_lock(&probe_lock);
> +	list_add_tail(&tp->list, &probe_list);
> +
> +	if (probe_is_return(tp))
> +		ret = register_kretprobe(&tp->rp);
> +	else
> +		ret = register_kprobe(&tp->kp);
> +
> +	if (ret) {
> +		pr_warning("Probe registering error: %d\n", ret);
> +		list_del(&tp->list);
> +	}
> +	mutex_unlock(&probe_lock);
> +	return ret;
> +}
> +
> +static void unregister_trace_probe(struct trace_probe *tp)
> +{
> +	if (probe_is_return(tp))
> +		unregister_kretprobe(&tp->rp);
> +	else
> +		unregister_kprobe(&tp->kp);
> +	list_del(&tp->list);
> +}
> +
> +#define PARAM_MAX_ARGS 16
> +#define PARAM_MAX_REGS MAX_REG_NUM
> +#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
> +
> +static int create_trace_probe(int argc, char **argv)
> +{
> +	/*
> +	 * Argument syntax:
> +	 *  - Add kprobe: p SYMBOL[+OFFS|-OFFS]|ADDRESS
> +	 *  - Add kretprobe: r SYMBOL[+0]
> +	 */
> +	struct trace_probe *tp;
> +	struct kprobe *kp;
> +	char *tmp;
> +	int ret = 0;
> +	int is_return = 0;
> +	char *symbol = NULL;
> +	long offset = 0;
> +	void *addr = NULL;
> +
> +	if (argc < 2)
> +		return -EINVAL;
> +
> +	if (argv[0][0] == 'p')
> +		is_return = 0;
> +	else if (argv[0][0] == 'r')
> +		is_return = 1;
> +	else
> +		return -EINVAL;
> +
> +	if (isdigit(argv[1][0])) {
> +		if (is_return)
> +			return -EINVAL;
> +		/* an address specified */
> +		ret = strict_strtoul(&argv[0][2], 0, (unsigned long *)&addr);
> +		if (ret)
> +			return ret;
> +	} else {
> +		/* a symbol specified */
> +		symbol = argv[1];
> +		/* TODO: support .init module functions */
> +		tmp = strchr(symbol, '+');
> +		if (!tmp)
> +			tmp = strchr(symbol, '-');
> +
> +		if (tmp) {
> +			ret = strict_strtol(tmp, 0, &offset);
> +			if (ret)
> +				return ret;
> +			*tmp = '\0';
> +		}
> +		if (offset && is_return)
> +			return -EINVAL;
> +	}
> +
> +	/* setup a probe */
> +	tp = alloc_trace_probe(symbol);
> +	if (IS_ERR(tp))
> +		return PTR_ERR(tp);
> +
> +	if (is_return) {
> +		kp = &tp->rp.kp;
> +		tp->rp.handler = kretprobe_trace_func;
> +	} else {
> +		kp = &tp->kp;
> +		tp->kp.pre_handler = kprobe_trace_func;
> +	}
> +
> +	if (tp->symbol) {
> +		/* TODO: check offset is collect by using insn_decoder */
> +		kp->symbol_name = tp->symbol;
> +		kp->offset = offset;
> +	} else
> +		kp->addr = addr;
> +
> +	ret = register_trace_probe(tp);
> +	if (ret)
> +		goto error;
> +	return 0;
> +
> +error:
> +	free_trace_probe(tp);
> +	return ret;
> +}
> +
> +static void cleanup_all_probes(void)
> +{
> +	struct trace_probe *tp;
> +	mutex_lock(&probe_lock);
> +	/* TODO: Use batch unregistration */
> +	while (!list_empty(&probe_list)) {
> +		tp = list_entry(probe_list.next, struct trace_probe, list);
> +		unregister_trace_probe(tp);
> +		free_trace_probe(tp);
> +	}
> +	mutex_unlock(&probe_lock);
> +}
> +
> +
> +/* Probes listing interfaces */
> +static void *probes_seq_start(struct seq_file *m, loff_t *pos)
> +{
> +	struct trace_probe *probe;
> +	loff_t n = *pos;
> +
> +	mutex_lock(&probe_lock);
> +	if (!list_empty(&probe_list)) {
> +		list_for_each_entry(probe, &probe_list, list)
> +			if (0 == n--)
> +				return probe;
> +	}
> +	return NULL;
> +}
> +
> +static void *probes_seq_next(struct seq_file *m, void *v, loff_t *pos)
> +{
> +	struct trace_probe *tp = v;
> +
> +	(*pos)++;
> +	if (tp->list.next == &probe_list)
> +		tp = NULL;
> +	else
> +		tp = list_entry(tp->list.next, struct trace_probe, list);
> +	return tp;
> +}
> +
> +static void probes_seq_stop(struct seq_file *m, void *v)
> +{
> +	mutex_unlock(&probe_lock);
> +}
> +
> +static int probes_seq_show(struct seq_file *m, void *v)
> +{
> +	struct trace_probe *tp = v;
> +
> +	if (tp == NULL)
> +		return 0;
> +
> +	if (tp->symbol)
> +		seq_printf(m, "%c %s%+ld\n",
> +			probe_is_return(tp) ? 'r' : 'p',
> +			probe_symbol(tp), probe_offset(tp));
> +	else
> +		seq_printf(m, "%c 0x%p\n",
> +			probe_is_return(tp) ? 'r' : 'p',
> +			probe_address(tp));
> +	return 0;
> +}
> +
> +static const struct seq_operations probes_seq_op = {
> +	.start  = probes_seq_start,
> +	.next   = probes_seq_next,
> +	.stop   = probes_seq_stop,
> +	.show   = probes_seq_show
> +};
> +
> +static int probes_open(struct inode *inode, struct file *file)
> +{
> +	if ((file->f_mode & FMODE_WRITE) &&
> +	    !(file->f_flags & O_APPEND))
> +		cleanup_all_probes();
> +
> +	return seq_open(file, &probes_seq_op);
> +}
> +
> +
> +#define WRITE_BUFSIZE 128
> +
> +ssize_t probes_write(struct file *file, const char __user *buffer,
> +		     size_t count, loff_t *ppos)
> +{
> +	char *kbuf, *tmp;
> +	char **argv = NULL;
> +	int argc = 0;
> +	int ret;
> +	size_t done;
> +	size_t size;
> +
> +	if (!count || count < 0)
> +		return 0;
> +
> +	kbuf = kmalloc(WRITE_BUFSIZE, GFP_KERNEL);
> +	if (!kbuf)
> +		return -ENOMEM;
> +
> +	ret = done = 0;
> +	do {
> +		size = count - done;
> +		if (size > WRITE_BUFSIZE)
> +			size = WRITE_BUFSIZE;
> +		if (copy_from_user(kbuf, buffer + done, size)) {
> +			ret = -EFAULT;
> +			goto out;
> +		}
> +		kbuf[size] = '\0';
> +		tmp = strchr(kbuf, '\n');
> +		if (!tmp) {
> +			pr_warning("Line length is too long: "
> +				   "Should be less than %d.", WRITE_BUFSIZE);
> +			ret = -EINVAL;
> +			goto out;
> +		}
> +		*tmp = '\0';
> +		size = tmp - kbuf + 1;
> +		done += size;
> +
> +		argv = argv_split(GFP_KERNEL, kbuf, &argc);
> +		if (!argv) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
> +
> +		if (argc)
> +			ret = create_trace_probe(argc, argv);
> +
> +		argv_free(argv);
> +		if (ret < 0)
> +			goto out;
> +
> +	} while (done < count);
> +	ret = done;
> +out:
> +	kfree(kbuf);
> +	return ret;
> +}
> +
> +static const struct file_operations kprobe_points_ops = {
> +	.owner          = THIS_MODULE,
> +	.open           = probes_open,
> +	.read           = seq_read,
> +	.llseek         = seq_lseek,
> +	.release        = seq_release,
> +	.write		= probes_write,
> +};
> +
> +/* event recording functions */
> +static void kprobe_trace_record(unsigned long ip, struct trace_probe *tp,
> +				struct pt_regs *regs)
> +{
> +	__trace_printk(ip, "%s%s%+ld\n",
> +			probe_is_return(tp) ? "<-" : "@",
> +			probe_symbol(tp), probe_offset(tp));


Ah, it means we should implement a sort of trace_printk where
we can put a custom ip.
Anyway I don't recommend you to use __trace_printk() because
trace_printk() wrap it by doing some choices of implementation.

If the format is a builtin string like here, it will choose a binary
insertion to the ring buffer (the format is not copied but only its address,
and the arguments are inserted by their binary values). It is more lightweight
and fast.

If you are using such builtin format, use __trace_bprintk instead.


> +}
> +
> +/* Make a debugfs interface for controling probe points */
> +static __init int init_kprobe_trace(void)
> +{
> +	struct dentry *d_tracer;
> +	struct dentry *entry;
> +
> +	d_tracer = tracing_init_dentry();
> +	if (!d_tracer)
> +		return 0;
> +
> +	entry = debugfs_create_file("kprobe_probes", 0444, d_tracer,
> +				    NULL, &kprobe_points_ops);
> +
> +	if (!entry)
> +		pr_warning("Could not create debugfs "
> +			   "'kprobe_probess' entry\n");
> +	return 0;
> +}
> +fs_initcall(init_kprobe_trace);
> +
> -- 
> Masami Hiramatsu
> 
> Software Engineer
> Hitachi Computer Products (America) Inc.
> Software Solutions Division
> 
> e-mail: mhiramat@...hat.com
> 
> 
> --
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