[RFC patch 33/41] LTTng dynamic tracing support with kprobes

[Mathieu Desnoyers]

Add Kprobe support to LTTng, so we can use

/mnt/debugfs/ltt/kprobe/enable
/mnt/debugfs/ltt/kprobe/disable
/mnt/debugfs/ltt/kprobe/list

to respectively enable, disable and list(!) all LTTng-kprobes.

An event kernel.kprobes will be logged. It records the instruction pointer
associated with the probe hit.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
---
 include/linux/ltt-tracer.h |    8 
 kernel/kallsyms.c          |    1 
 ltt/Kconfig                |   15 +
 ltt/Makefile               |    1 
 ltt/ltt-kprobes.c          |  479 +++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 504 insertions(+)

Index: linux-2.6-lttng/ltt/Kconfig
===================================================================
--- linux-2.6-lttng.orig/ltt/Kconfig	2009-03-05 16:09:59.000000000 -0500
+++ linux-2.6-lttng/ltt/Kconfig	2009-03-05 16:10:12.000000000 -0500
@@ -136,4 +136,19 @@ config LTT_VMCORE
 
 	  Special crash extension should be used to extract ltt buffers.
 
+config LTT_KPROBES
+	bool "Linux Trace Toolkit Kprobes Support"
+	depends on HAVE_KPROBES
+	select LTT_TRACE_CONTROL
+	select LTT_FAST_SERIALIZE
+	select KPROBES
+	select KALLSYMS
+	default y
+	help
+	  Allows connecting the LTTng tracer on kprobes using simple debugfs
+	  file operations :
+	    ltt/kprobes/enable
+	    ltt/kprobes/disable
+	    ltt/kprobes/list
+
 endif # LTT
Index: linux-2.6-lttng/ltt/Makefile
===================================================================
--- linux-2.6-lttng.orig/ltt/Makefile	2009-03-05 16:10:10.000000000 -0500
+++ linux-2.6-lttng/ltt/Makefile	2009-03-05 16:10:12.000000000 -0500
@@ -14,3 +14,4 @@ obj-$(CONFIG_LTT_FAST_SERIALIZE)	+= ltt-
 obj-$(CONFIG_LTT_TRACE_CONTROL)		+= ltt-trace-control.o
 obj-$(CONFIG_LTT_USERSPACE_EVENT)	+= ltt-userspace-event.o
 obj-$(CONFIG_LTT_FILTER)		+= ltt-filter.o
+obj-$(CONFIG_LTT_KPROBES)		+= ltt-kprobes.o
Index: linux-2.6-lttng/ltt/ltt-kprobes.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/ltt/ltt-kprobes.c	2009-03-05 16:10:12.000000000 -0500
@@ -0,0 +1,479 @@
+/*
+ * (C) Copyright	2009 -
+ * 		Mathieu Desnoyers (mathieu.desnoyers@xxxxxxxxxx)
+ *
+ * LTTng kprobes integration module.
+ */
+
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/ltt-tracer.h>
+#include <linux/marker.h>
+#include <linux/mutex.h>
+#include <linux/jhash.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/debugfs.h>
+#include <linux/kallsyms.h>
+#include <linux/ltt-type-serializer.h>
+
+#define LTT_KPROBES_DIR 	"kprobes"
+#define LTT_KPROBES_ENABLE	"enable"
+#define LTT_KPROBES_DISABLE	"disable"
+#define LTT_KPROBES_LIST	"list"
+
+/* Active LTTng kprobes hash table */
+static DEFINE_MUTEX(ltt_kprobes_mutex);
+
+#define LTT_KPROBE_HASH_BITS	6
+#define LTT_KPROBE_TABLE_SIZE	(1 << LTT_KPROBE_HASH_BITS)
+static struct hlist_head ltt_kprobe_table[LTT_KPROBE_TABLE_SIZE];
+
+struct kprobe_entry {
+	struct hlist_node hlist;
+	struct kprobe kp;
+	char key[0];
+};
+
+static struct dentry *ltt_kprobes_dir,
+		     *ltt_kprobes_enable_dentry,
+		     *ltt_kprobes_disable_dentry,
+		     *ltt_kprobes_list_dentry;
+
+static int module_exit;
+
+
+static void trace_kprobe_table_entry(void *call_data, struct kprobe_entry *e)
+{
+	char namebuf[KSYM_NAME_LEN];
+	unsigned long addr;
+
+	if (e->kp.addr) {
+		sprint_symbol(namebuf,
+			      (unsigned long)e->kp.addr);
+		addr = (unsigned long)e->kp.addr;
+	} else {
+		strcpy(namebuf, e->kp.symbol_name);
+		/* TODO : add offset */
+		addr = kallsyms_lookup_name(namebuf);
+	}
+	if (addr)
+		__trace_mark(0, kprobe_state, kprobe_table,
+			call_data,
+			"ip 0x%lX symbol %s", addr, namebuf);
+}
+
+DEFINE_MARKER(kernel, kprobe, "ip %lX");
+
+static int ltt_kprobe_handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+	struct marker *marker;
+	unsigned long data;
+
+	data = (unsigned long)p->addr;
+	marker = &GET_MARKER(kernel, kprobe);
+	ltt_specialized_trace(marker, marker->single.probe_private,
+		&data, sizeof(data), sizeof(data));
+	return 0;
+}
+
+static int ltt_register_kprobe(const char *key)
+{
+	struct hlist_head *head;
+	struct hlist_node *node;
+	struct kprobe_entry *e = NULL;
+	char *symbol_name = NULL;
+	unsigned long addr;
+	unsigned int offset = 0;
+	u32 hash;
+	size_t key_len = strlen(key) + 1;
+	int ret;
+
+	if (key_len == 1)
+		return -ENOENT;	/* only \0 */
+
+	if (sscanf(key, "%li", &addr) != 1)
+		addr = 0;
+
+	if (!addr) {
+		const char *symbol_end = NULL;
+		unsigned int symbol_len;	/* includes final \0 */
+
+		symbol_end = strchr(key, ' ');
+		if (symbol_end)
+			symbol_len = symbol_end - key + 1;
+		else
+			symbol_len = key_len;
+		symbol_name = kmalloc(symbol_len, GFP_KERNEL);
+		if (!symbol_name) {
+			ret = -ENOMEM;
+			goto error;
+		}
+		memcpy(symbol_name, key, symbol_len - 1);
+		symbol_name[symbol_len-1] = '\0';
+		if (symbol_end) {
+			symbol_end++;	/* start of offset */
+			if (sscanf(symbol_end, "%i", &offset) != 1)
+				offset = 0;
+		}
+	}
+
+	hash = jhash(key, key_len-1, 0);
+	head = &ltt_kprobe_table[hash & ((1 << LTT_KPROBE_HASH_BITS)-1)];
+	hlist_for_each_entry(e, node, head, hlist) {
+		if (!strcmp(key, e->key)) {
+			printk(KERN_NOTICE "Kprobe %s busy\n", key);
+			ret = -EBUSY;
+			goto error;
+		}
+	}
+	/*
+	 * Using kzalloc here to allocate a variable length element. Could
+	 * cause some memory fragmentation if overused.
+	 */
+	e = kzalloc(sizeof(struct kprobe_entry) + key_len, GFP_KERNEL);
+	if (!e) {
+		ret = -ENOMEM;
+		goto error;
+	}
+	memcpy(e->key, key, key_len);
+	hlist_add_head(&e->hlist, head);
+	e->kp.pre_handler = ltt_kprobe_handler_pre;
+	e->kp.symbol_name = symbol_name;
+	e->kp.offset = offset;
+	e->kp.addr = (void *)addr;
+	ret = register_kprobe(&e->kp);
+	if (ret < 0)
+		goto error_list_del;
+	trace_kprobe_table_entry(NULL, e);
+	return 0;
+
+error_list_del:
+	hlist_del(&e->hlist);
+error:
+	kfree(symbol_name);
+	kfree(e);
+	return ret;
+}
+
+static int ltt_unregister_kprobe(const char *key)
+{
+	struct hlist_head *head;
+	struct hlist_node *node;
+	struct kprobe_entry *e;
+	int found = 0;
+	size_t key_len = strlen(key) + 1;
+	u32 hash;
+
+	hash = jhash(key, key_len-1, 0);
+	head = &ltt_kprobe_table[hash & ((1 << LTT_KPROBE_HASH_BITS)-1)];
+	hlist_for_each_entry(e, node, head, hlist) {
+		if (!strcmp(key, e->key)) {
+			found = 1;
+			break;
+		}
+	}
+	if (!found)
+		return -ENOENT;
+	hlist_del(&e->hlist);
+	unregister_kprobe(&e->kp);
+	kfree(e->kp.symbol_name);
+	kfree(e);
+	return 0;
+}
+
+static void ltt_unregister_all_kprobes(void)
+{
+	struct kprobe_entry *e;
+	struct hlist_head *head;
+	struct hlist_node *node, *tmp;
+	unsigned int i;
+
+	for (i = 0; i < LTT_KPROBE_TABLE_SIZE; i++) {
+		head = &ltt_kprobe_table[i];
+		hlist_for_each_entry_safe(e, node, tmp, head, hlist) {
+			hlist_del(&e->hlist);
+			unregister_kprobe(&e->kp);
+			kfree(e->kp.symbol_name);
+			kfree(e);
+		}
+	}
+}
+
+/*
+ * Allows to specify either
+ * - symbol
+ * - symbol offset
+ * - address
+ */
+static ssize_t enable_op_write(struct file *file,
+	const char __user *user_buf, size_t count, loff_t *ppos)
+{
+	int err, buf_size;
+	char buf[NAME_MAX];
+	char *end;
+
+	mutex_lock(&ltt_kprobes_mutex);
+	if (module_exit) {
+		err = -EPERM;
+		goto error;
+	}
+
+	buf_size = min(count, sizeof(buf) - 1);
+	err = copy_from_user(buf, user_buf, buf_size);
+	if (err)
+		goto error;
+	buf[buf_size] = '\0';
+	end = strchr(buf, '\n');
+	if (end)
+		*end = '\0';
+	err = ltt_register_kprobe(buf);
+	if (err)
+		goto error;
+	mutex_unlock(&ltt_kprobes_mutex);
+
+	return count;
+error:
+	mutex_unlock(&ltt_kprobes_mutex);
+	return err;
+}
+
+static const struct file_operations ltt_kprobes_enable = {
+	.write = enable_op_write,
+};
+
+static ssize_t disable_op_write(struct file *file,
+	const char __user *user_buf, size_t count, loff_t *ppos)
+{
+	int err, buf_size;
+	char buf[NAME_MAX];
+	char *end;
+
+	mutex_lock(&ltt_kprobes_mutex);
+	if (module_exit)
+		goto end;
+
+	buf_size = min(count, sizeof(buf) - 1);
+	err = copy_from_user(buf, user_buf, buf_size);
+	if (err)
+		goto error;
+	buf[buf_size] = '\0';
+	end = strchr(buf, '\n');
+	if (end)
+		*end = '\0';
+	err = ltt_unregister_kprobe(buf);
+	if (err)
+		goto error;
+end:
+	mutex_unlock(&ltt_kprobes_mutex);
+	return count;
+error:
+	mutex_unlock(&ltt_kprobes_mutex);
+	return err;
+}
+
+static const struct file_operations ltt_kprobes_disable = {
+	.write = disable_op_write,
+};
+
+/*
+ * This seqfile read is not perfectly safe, as a kprobe could be removed from
+ * the hash table between two reads. This will result in an incomplete output.
+ */
+static struct kprobe_entry *ltt_find_next_kprobe(struct kprobe_entry *prev)
+{
+	struct kprobe_entry *e;
+	struct hlist_head *head;
+	struct hlist_node *node;
+	unsigned int i;
+	int found = 0;
+
+	if (prev == (void *)-1UL)
+		return NULL;
+
+	if (!prev)
+		found = 1;
+
+	for (i = 0; i < LTT_KPROBE_TABLE_SIZE; i++) {
+		head = &ltt_kprobe_table[i];
+		hlist_for_each_entry(e, node, head, hlist) {
+			if (found)
+				return e;
+			if (e == prev)
+				found = 1;
+		}
+	}
+	return NULL;
+}
+
+static void *lk_next(struct seq_file *m, void *p, loff_t *pos)
+{
+	m->private = ltt_find_next_kprobe(m->private);
+	if (!m->private) {
+		m->private = (void *)-1UL;
+		return NULL;
+	}
+	return m->private;
+}
+
+static void *lk_start(struct seq_file *m, loff_t *pos)
+{
+	mutex_lock(&ltt_kprobes_mutex);
+	if (!*pos)
+		m->private = NULL;
+	m->private = ltt_find_next_kprobe(m->private);
+	if (!m->private) {
+		m->private = (void *)-1UL;
+		return NULL;
+	}
+	return m->private;
+}
+
+static void lk_stop(struct seq_file *m, void *p)
+{
+	mutex_unlock(&ltt_kprobes_mutex);
+}
+
+static int lk_show(struct seq_file *m, void *p)
+{
+	struct kprobe_entry *e = m->private;
+	seq_printf(m, "%s\n", e->key);
+	return 0;
+}
+
+static const struct seq_operations ltt_kprobes_list_op = {
+	.start = lk_start,
+	.next = lk_next,
+	.stop = lk_stop,
+	.show = lk_show,
+};
+
+static int ltt_kprobes_list_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	ret = seq_open(file, &ltt_kprobes_list_op);
+	if (ret == 0)
+		((struct seq_file *)file->private_data)->private = NULL;
+	return ret;
+}
+
+static int ltt_kprobes_list_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq = file->private_data;
+
+	seq->private = NULL;
+	return seq_release(inode, file);
+}
+
+static const struct file_operations ltt_kprobes_list = {
+	.open = ltt_kprobes_list_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = ltt_kprobes_list_release,
+};
+
+void ltt_dump_kprobes_table(void *call_data)
+{
+	struct kprobe_entry *e;
+	struct hlist_head *head;
+	struct hlist_node *node;
+	unsigned int i;
+
+	for (i = 0; i < LTT_KPROBE_TABLE_SIZE; i++) {
+		head = &ltt_kprobe_table[i];
+		hlist_for_each_entry(e, node, head, hlist)
+			trace_kprobe_table_entry(call_data, e);
+	}
+}
+EXPORT_SYMBOL_GPL(ltt_dump_kprobes_table);
+
+static int __init ltt_kprobes_init(void)
+{
+	struct dentry *ltt_root_dentry;
+	int ret = 0;
+
+	printk(KERN_INFO "LTT : ltt-kprobes init\n");
+	mutex_lock(&ltt_kprobes_mutex);
+
+	ltt_root_dentry = get_ltt_root();
+	if (!ltt_root_dentry) {
+		ret = -ENOENT;
+		goto err_no_root;
+	}
+
+	ltt_kprobes_dir = debugfs_create_dir(LTT_KPROBES_DIR, ltt_root_dentry);
+	if (!ltt_kprobes_dir) {
+		printk(KERN_ERR
+		       "ltt_kprobes_init: failed to create dir %s\n",
+			LTT_KPROBES_DIR);
+		ret = -ENOMEM;
+		goto err_no_dir;
+	}
+
+	ltt_kprobes_enable_dentry = debugfs_create_file(LTT_KPROBES_ENABLE,
+		S_IWUSR, ltt_kprobes_dir, NULL,
+		&ltt_kprobes_enable);
+	if (IS_ERR(ltt_kprobes_enable_dentry) || !ltt_kprobes_enable_dentry) {
+		printk(KERN_ERR
+		       "ltt_kprobes_init: failed to create file %s\n",
+			LTT_KPROBES_ENABLE);
+		ret = -ENOMEM;
+		goto err_no_enable;
+	}
+
+	ltt_kprobes_disable_dentry = debugfs_create_file(LTT_KPROBES_DISABLE,
+		S_IWUSR, ltt_kprobes_dir, NULL,
+		&ltt_kprobes_disable);
+	if (IS_ERR(ltt_kprobes_disable_dentry) || !ltt_kprobes_disable_dentry) {
+		printk(KERN_ERR
+		       "ltt_kprobes_init: failed to create file %s\n",
+			LTT_KPROBES_DISABLE);
+		ret = -ENOMEM;
+		goto err_no_disable;
+	}
+
+	ltt_kprobes_list_dentry = debugfs_create_file(LTT_KPROBES_LIST,
+		S_IWUSR, ltt_kprobes_dir, NULL,
+		&ltt_kprobes_list);
+	if (IS_ERR(ltt_kprobes_list_dentry) || !ltt_kprobes_list_dentry) {
+		printk(KERN_ERR
+		       "ltt_kprobes_init: failed to create file %s\n",
+			LTT_KPROBES_LIST);
+		ret = -ENOMEM;
+		goto err_no_list;
+	}
+
+	mutex_unlock(&ltt_kprobes_mutex);
+	return ret;
+
+err_no_list:
+	debugfs_remove(ltt_kprobes_disable_dentry);
+err_no_disable:
+	debugfs_remove(ltt_kprobes_enable_dentry);
+err_no_enable:
+	debugfs_remove(ltt_kprobes_dir);
+err_no_dir:
+err_no_root:
+	mutex_unlock(&ltt_kprobes_mutex);
+	return ret;
+}
+module_init(ltt_kprobes_init);
+
+static void __exit ltt_kprobes_exit(void)
+{
+	printk(KERN_INFO "LTT : ltt-kprobes exit\n");
+	mutex_lock(&ltt_kprobes_mutex);
+	module_exit = 1;
+	debugfs_remove(ltt_kprobes_list_dentry);
+	debugfs_remove(ltt_kprobes_disable_dentry);
+	debugfs_remove(ltt_kprobes_enable_dentry);
+	debugfs_remove(ltt_kprobes_dir);
+	ltt_unregister_all_kprobes();
+	mutex_unlock(&ltt_kprobes_mutex);
+}
+module_exit(ltt_kprobes_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mathieu Desnoyers");
+MODULE_DESCRIPTION("Linux Trace Toolkit Kprobes Support");
Index: linux-2.6-lttng/include/linux/ltt-tracer.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/ltt-tracer.h	2009-03-05 16:09:59.000000000 -0500
+++ linux-2.6-lttng/include/linux/ltt-tracer.h	2009-03-05 16:10:12.000000000 -0500
@@ -672,6 +672,14 @@ extern void ltt_dump_marker_state(struct
 void ltt_lock_traces(void);
 void ltt_unlock_traces(void);
 
+#ifdef CONFIG_LTT_KPROBES
+extern void ltt_dump_kprobes_table(void *call_data);
+#else
+static inline void ltt_dump_kprobes_table(void *call_data)
+{
+}
+#endif
+
 /* Relay IOCTL */
 
 /* Get the next sub buffer that can be read. */
Index: linux-2.6-lttng/kernel/kallsyms.c
===================================================================
--- linux-2.6-lttng.orig/kernel/kallsyms.c	2009-03-05 16:08:41.000000000 -0500
+++ linux-2.6-lttng/kernel/kallsyms.c	2009-03-05 16:10:12.000000000 -0500
@@ -160,6 +160,7 @@ unsigned long kallsyms_lookup_name(const
 	}
 	return module_kallsyms_lookup_name(name);
 }
+EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
 
 static unsigned long get_symbol_pos(unsigned long addr,
 				    unsigned long *symbolsize,

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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