[PATCH 5/7] gcov: add gcov profiling infrastructure

[Peter Oberparleiter]

From: Peter Oberparleiter <peter.oberparleiter@xxxxxxxxxx>

gcov profiling infrastructure:

* change kbuild to include profiling flags
* provide functions needed by profiling code
* present profiling data as files in debugfs

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@xxxxxxxxxx>
---
 Documentation/gcov.txt              |  127 +++++
 Documentation/kernel-parameters.txt |    7 
 Makefile                            |   10 
 arch/Kconfig                        |    2 
 init/main.c                         |    8 
 kernel/Makefile                     |    1 
 kernel/gcov/Kconfig                 |   45 +
 kernel/gcov/Makefile                |    3 
 kernel/gcov/base.c                  |  145 ++++++
 kernel/gcov/fs.c                    |  609 ++++++++++++++++++++++++++
 kernel/gcov/gcc_3_4.c               |  420 +++++++++++++++++
 kernel/gcov/gcov.h                  |  128 +++++
 scripts/Makefile.lib                |    8 
 13 files changed, 1509 insertions(+), 4 deletions(-)

Index: linux-2.6.26-rc3/Makefile
===================================================================
--- linux-2.6.26-rc3.orig/Makefile
+++ linux-2.6.26-rc3/Makefile
@@ -320,6 +320,7 @@ AFLAGS_MODULE   = $(MODFLAGS)
 LDFLAGS_MODULE  =
 CFLAGS_KERNEL	=
 AFLAGS_KERNEL	=
+CFLAGS_GCOV	= -fprofile-arcs -ftest-coverage
 
 
 # Use LINUXINCLUDE when you must reference the include/ directory.
@@ -345,7 +346,7 @@ export CPP AR NM STRIP OBJCOPY OBJDUMP M
 export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
-export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
+export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV
 export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 
 # When compiling out-of-tree modules, put MODVERDIR in the module
@@ -1132,7 +1133,8 @@ clean: archclean $(clean-dirs)
 	@find . $(RCS_FIND_IGNORE) \
 		\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
 		-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
-		-o -name '*.symtypes' -o -name 'modules.order' \) \
+		-o -name '*.symtypes' -o -name 'modules.order' \
+		-o -name '*.gcno' \) \
 		-type f -print | xargs rm -f
 
 # mrproper - Delete all generated files, including .config
@@ -1336,8 +1338,8 @@ clean: $(clean-dirs)
 	$(call cmd,rmfiles)
 	@find $(KBUILD_EXTMOD) $(RCS_FIND_IGNORE) \
 		\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
-		-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \) \
-		-type f -print | xargs rm -f
+		-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
+		-o -name '*.gcno' \) -type f -print | xargs rm -f
 
 help:
 	@echo  '  Building external modules.'
Index: linux-2.6.26-rc3/scripts/Makefile.lib
===================================================================
--- linux-2.6.26-rc3.orig/scripts/Makefile.lib
+++ linux-2.6.26-rc3/scripts/Makefile.lib
@@ -100,6 +100,14 @@ _c_flags       = $(KBUILD_CFLAGS) $(ccfl
 _a_flags       = $(KBUILD_AFLAGS) $(asflags-y) $(AFLAGS_$(basetarget).o)
 _cpp_flags     = $(KBUILD_CPPFLAGS) $(cppflags-y) $(CPPFLAGS_$(@F))
 
+# Enable profiling flags for a file, directory or for all files depending on
+# variables GCOV_obj.o, GCOV and CONFIG_GCOV_PROFILE_ALL (in this order)
+ifeq ($(CONFIG_GCOV_PROFILE),y)
+_c_flags += $(if $(patsubst n%,, \
+		$(GCOV_$(basetarget).o)$(GCOV)$(CONFIG_GCOV_PROFILE_ALL)), \
+		$(CFLAGS_GCOV))
+endif
+
 # If building the kernel in a separate objtree expand all occurrences
 # of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').
 
Index: linux-2.6.26-rc3/kernel/gcov/Kconfig
===================================================================
--- /dev/null
+++ linux-2.6.26-rc3/kernel/gcov/Kconfig
@@ -0,0 +1,45 @@
+menu "GCOV profiling"
+
+config GCOV_PROFILE
+	bool "Activate gcov-based profiling"
+	depends on DEBUG_FS
+	---help---
+	This option enables gcov-based code profiling (e.g. for code coverage
+	measurements).
+
+	If unsure, say N.
+
+	Additionally specify CONFIG_GCOV_PROFILE_ALL=y to get profiling data
+	for the entire kernel. To enable profiling for specific files or
+	directories, add a line similar to the following to the respective
+	Makefile:
+
+	For a single file (e.g. main.o):
+	        GCOV_main.o := y
+
+	For all files in one directory:
+	        GCOV := y
+
+	To exclude files from being profiled even when CONFIG_GCOV_PROFILE_ALL
+	is specified, use:
+
+	        GCOV_main.o := n
+	and:
+	        GCOV := n
+
+	Note that the debugfs filesystem has to be mounted to access
+	profiling data.
+
+config GCOV_PROFILE_ALL
+	bool "Profile entire Kernel"
+	depends on GCOV_PROFILE
+	---help---
+	This options activates profiling for the entire kernel.
+
+	If unsure, say Y.
+
+	Note that a kernel compiled with profiling flags will be significantly
+        larger and run slower. Also be sure to exclude files from profiling
+        which are not linked to the kernel image to prevent linker errors.
+
+endmenu
Index: linux-2.6.26-rc3/kernel/gcov/base.c
===================================================================
--- /dev/null
+++ linux-2.6.26-rc3/kernel/gcov/base.c
@@ -0,0 +1,145 @@
+/*
+ *  This code maintains a list of active profiling data structures.
+ *
+ *    Copyright IBM Corp. 2008
+ *    Author(s): Peter Oberparleiter <peter.oberparleiter@xxxxxxxxxx>
+ *
+ *    Uses gcc-internal data definitions.
+ *    Based on the gcov-kernel patch by:
+ *		 Hubertus Franke <frankeh@xxxxxxxxxx>
+ *		 Nigel Hinds <nhinds@xxxxxxxxxx>
+ *		 Rajan Ravindran <rajancr@xxxxxxxxxx>
+ *		 Peter Oberparleiter <peter.oberparleiter@xxxxxxxxxx>
+ *		 Paul Larson
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/syscalls.h>
+#include "gcov.h"
+
+static struct gcov_info *gcov_info_head;
+static int gcov_events_enabled;
+static DEFINE_MUTEX(gcov_lock);
+
+/* __gcov_init is called by gcc-generated constructor code for each object
+ * file compiled with -fprofile-arcs. */
+void __gcov_init(struct gcov_info *info)
+{
+	static unsigned int gcov_version;
+
+	mutex_lock(&gcov_lock);
+	if (gcov_version == 0) {
+		gcov_version = info->version;
+		/* Printing gcc's version magic may prove useful for debugging
+		 * incompatibility reports. */
+		printk(KERN_INFO TAG "version magic: 0x%x\n", gcov_version);
+	}
+	/* Add new profiling data structure to list and inform event
+	 * listener. */
+	info->next = gcov_info_head;
+	gcov_info_head = info;
+	if (gcov_events_enabled)
+		gcov_event(gcov_add, info);
+	mutex_unlock(&gcov_lock);
+}
+EXPORT_SYMBOL(__gcov_init);
+
+/* These functions may be referenced by gcc-generated profiling code but serve
+ * no function for kernel profiling. */
+void __gcov_flush(void)
+{
+	/* Unused. */
+}
+EXPORT_SYMBOL(__gcov_flush);
+
+void __gcov_merge_add(gcov_type *counters, unsigned int n_counters)
+{
+	/* Unused. */
+}
+EXPORT_SYMBOL(__gcov_merge_add);
+
+void __gcov_merge_single(gcov_type *counters, unsigned int n_counters)
+{
+	/* Unused. */
+}
+EXPORT_SYMBOL(__gcov_merge_single);
+
+void __gcov_merge_delta(gcov_type *counters, unsigned int n_counters)
+{
+	/* Unused. */
+}
+EXPORT_SYMBOL(__gcov_merge_delta);
+
+int __gcov_execve(const char *path, char *const argv[], char *const envp[])
+{
+	return kernel_execve(path, argv, envp);
+}
+EXPORT_SYMBOL(__gcov_execve);
+
+/**
+ * gcov_enable_events - enable event reporting through gcov_event()
+ *
+ * Turn on reporting of profiling data load/unload-events through the
+ * gcov_event() callback. Also replay all previous events once. This function
+ * is needed because some events are potentially generated too early for the
+ * callback implementation to handle them initially.
+ */
+void gcov_enable_events(void)
+{
+	struct gcov_info *info;
+
+	mutex_lock(&gcov_lock);
+	gcov_events_enabled = 1;
+	/* Perform event callback for previously registered entries. */
+	for (info = gcov_info_head; info; info = info->next)
+		gcov_event(gcov_add, info);
+	mutex_unlock(&gcov_lock);
+}
+
+static inline int within(void *addr, void *start, unsigned long size)
+{
+	return ((addr >= start) && (addr < start + size));
+}
+
+/* Update list and generate events when modules are unloaded. */
+static int gcov_module_notifier(struct notifier_block *nb, unsigned long event,
+				void *data)
+{
+#ifdef CONFIG_MODULES
+	struct module *mod = data;
+	struct gcov_info *info;
+	struct gcov_info *prev;
+
+	if (event != MODULE_STATE_GOING)
+		return NOTIFY_OK;
+	mutex_lock(&gcov_lock);
+	prev = NULL;
+	/* Remove entries located in module from linked list. */
+	for (info = gcov_info_head; info; info = info->next) {
+		if (within(info, mod->module_core, mod->core_size)) {
+			if (prev)
+				prev->next = info->next;
+			else
+				gcov_info_head = info->next;
+			if (gcov_events_enabled)
+				gcov_event(gcov_remove, info);
+		} else
+			prev = info;
+	}
+	mutex_unlock(&gcov_lock);
+#endif /* CONFIG_MODULES */
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block gcov_nb = {
+	.notifier_call	= gcov_module_notifier,
+};
+
+static int __init gcov_init(void)
+{
+	return register_module_notifier(&gcov_nb);
+}
+__initcall(gcov_init);
Index: linux-2.6.26-rc3/kernel/gcov/gcov.h
===================================================================
--- /dev/null
+++ linux-2.6.26-rc3/kernel/gcov/gcov.h
@@ -0,0 +1,128 @@
+/*
+ *  Profiling infrastructure declarations.
+ *
+ *  This file is based on gcc-internal definitions. Data structures are
+ *  defined to be compatible with gcc counterparts. For a better
+ *  understanding, refer to gcc source: gcc/gcov-io.h.
+ *
+ *    Copyright IBM Corp. 2008
+ *    Author(s): Peter Oberparleiter <peter.oberparleiter@xxxxxxxxxx>
+ *
+ *    Uses gcc-internal data definitions.
+ */
+
+#ifndef GCOV_H
+#define GCOV_H GCOV_H
+
+#include <linux/types.h>
+
+#define TAG	"gcov: "
+
+/* Profiling data types used for gcc 3.4 and above - these are defined by
+ * gcc and need to be kept as close to the original definition as possible to
+ * remain compatible. */
+#define GCOV_COUNTERS		5
+#define GCOV_DATA_MAGIC		((unsigned int) 0x67636461)
+#define GCOV_TAG_FUNCTION	((unsigned int) 0x01000000)
+#define GCOV_TAG_COUNTER_BASE	((unsigned int) 0x01a10000)
+#define GCOV_TAG_FOR_COUNTER(count)					\
+	(GCOV_TAG_COUNTER_BASE + ((unsigned int) (count) << 17))
+
+#if BITS_PER_LONG >= 64
+typedef long gcov_type;
+#else
+typedef long long gcov_type;
+#endif
+
+/**
+ * struct gcov_fn_info - profiling meta data per function
+ * @ident: object file-unique function identifier
+ * @checksum: function checksum
+ * @n_ctrs: number of values per counter type belonging to this function
+ *
+ * This data is generated by gcc during compilation and doesn't change
+ * at run-time.
+ */
+struct gcov_fn_info {
+	unsigned int ident;
+	unsigned int checksum;
+	unsigned int n_ctrs[0];
+};
+
+/**
+ * struct gcov_ctr_info - profiling data per counter type
+ * @num: number of counter values for this type
+ * @values: array of counter values for this type
+ * @merge: merge function for counter values of this type (unused)
+ *
+ * This data is generated by gcc during compilation and doesn't change
+ * at run-time with the exception of the values array.
+ */
+struct gcov_ctr_info {
+	unsigned int num;
+	gcov_type *values;
+	void (*merge)(gcov_type *, unsigned int);
+};
+
+/**
+ * struct gcov_info - profiling data per object file
+ * @version: gcov version magic indicating the gcc version used for compilation
+ * @next: list head for a singly-linked list
+ * @stamp: time stamp
+ * @filename: name of the associated gcov data file
+ * @n_functions: number of instrumented functions
+ * @functions: function data
+ * @ctr_mask: mask specifying which counter types are active
+ * @counts: counter data per counter type
+ *
+ * This data is generated by gcc during compilation and doesn't change
+ * at run-time with the exception of the next pointer.
+ */
+struct gcov_info {
+	unsigned int version;
+	struct gcov_info *next;
+	unsigned int stamp;
+	const char *filename;
+	unsigned int n_functions;
+	const struct gcov_fn_info *functions;
+	unsigned int ctr_mask;
+	struct gcov_ctr_info counts[0];
+};
+
+/* Base interface. */
+enum gcov_action {
+	gcov_add,
+	gcov_remove,
+};
+
+void gcov_event(enum gcov_action action, struct gcov_info *info);
+void gcov_enable_events(void);
+
+/* Iterator control. */
+struct seq_file;
+struct gcov_iterator;
+
+struct gcov_iterator *gcov_iter_new(struct gcov_info *info);
+void gcov_iter_free(struct gcov_iterator *iter);
+void gcov_iter_start(struct gcov_iterator *iter);
+int gcov_iter_next(struct gcov_iterator *iter);
+int gcov_iter_write(struct gcov_iterator *iter, struct seq_file *seq);
+struct gcov_info *gcov_iter_get_info(struct gcov_iterator *iter);
+
+/* gcov_info control. */
+void gcov_info_reset(struct gcov_info *info);
+int gcov_info_is_compatible(struct gcov_info *info1, struct gcov_info *info2);
+void gcov_info_add(struct gcov_info *dest, struct gcov_info *source);
+struct gcov_info *gcov_info_dup(struct gcov_info *info);
+void gcov_info_free(struct gcov_info *info);
+
+struct gcov_link {
+	enum {
+		obj_tree,
+		src_tree,
+	} dir;
+	const char *ext;
+};
+extern const struct gcov_link gcov_link[];
+
+#endif /* GCOV_H */
Index: linux-2.6.26-rc3/kernel/Makefile
===================================================================
--- linux-2.6.26-rc3.orig/kernel/Makefile
+++ linux-2.6.26-rc3/kernel/Makefile
@@ -69,6 +69,7 @@ obj-$(CONFIG_TASK_DELAY_ACCT) += delayac
 obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o
 obj-$(CONFIG_MARKERS) += marker.o
 obj-$(CONFIG_LATENCYTOP) += latencytop.o
+obj-$(CONFIG_GCOV_PROFILE) += gcov/
 
 ifneq ($(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER),y)
 # According to Alan Modra <alan@xxxxxxxxxxxxxxxx>, the -fno-omit-frame-pointer is
Index: linux-2.6.26-rc3/kernel/gcov/Makefile
===================================================================
--- /dev/null
+++ linux-2.6.26-rc3/kernel/gcov/Makefile
@@ -0,0 +1,3 @@
+EXTRA_CFLAGS := -DSRCTREE='"$(srctree)"' -DOBJTREE='"$(objtree)"'
+
+obj-$(CONFIG_GCOV_PROFILE) := base.o fs.o gcc_3_4.o
Index: linux-2.6.26-rc3/kernel/gcov/fs.c
===================================================================
--- /dev/null
+++ linux-2.6.26-rc3/kernel/gcov/fs.c
@@ -0,0 +1,609 @@
+/*
+ *  This code exports profiling data as debugfs files to userspace.
+ *
+ *    Copyright IBM Corp. 2008
+ *    Author(s): Peter Oberparleiter <peter.oberparleiter@xxxxxxxxxx>
+ *
+ *    Uses gcc-internal data definitions.
+ *    Based on the gcov-kernel patch by:
+ *		 Hubertus Franke <frankeh@xxxxxxxxxx>
+ *		 Nigel Hinds <nhinds@xxxxxxxxxx>
+ *		 Rajan Ravindran <rajancr@xxxxxxxxxx>
+ *		 Peter Oberparleiter <peter.oberparleiter@xxxxxxxxxx>
+ *		 Paul Larson
+ *		 Yi CDL Yang
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/debugfs.h>
+#include <linux/fs.h>
+#include <linux/list.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/mutex.h>
+#include <linux/seq_file.h>
+#include "gcov.h"
+
+/**
+ * struct gcov_node - represents a debugfs entry
+ * @list: list head for child node list
+ * @children: child nodes
+ * @all: list head for list of all nodes
+ * @parent: parent node
+ * @info: associated profiling data structure if not a directory
+ * @ghost: when an object file containing profiling data is unloaded we keep a
+ *         copy of the profiling data here to allow collecting coverage data
+ *         for cleanup code. Such a node is called a "ghost".
+ * @dentry: main debugfs entry, either a directory or data file
+ * @links: associated symbolic links
+ * @name: data file basename
+ *
+ * struct gcov_node represents an entity within the gcov/ subdirectory
+ * of debugfs. There are directory and data file nodes. The latter represent
+ * the actual synthesized data file plus any associated symbolic links which
+ * are needed by the gcov tool to work correctly.
+ */
+struct gcov_node {
+	struct list_head list;
+	struct list_head children;
+	struct list_head all;
+	struct gcov_node *parent;
+	struct gcov_info *info;
+	struct gcov_info *ghost;
+	struct dentry *dentry;
+	struct dentry **links;
+	char name[0];
+};
+
+static const char objtree[] = OBJTREE;
+static const char srctree[] = SRCTREE;
+static struct gcov_node root_node;
+static struct dentry *reset_dentry;
+static LIST_HEAD(all_head);
+static DEFINE_MUTEX(node_lock);
+
+/* If non-zero, keep copies of profiling data for unloaded modules. */
+static int gcov_persist = 1;
+
+static int __init gcov_persist_setup(char *str)
+{
+	int val;
+	char delim;
+
+	if (sscanf(str, "%d %c", &val, &delim) != 1) {
+		printk(KERN_WARNING TAG "invalid gcov_persist parameter '%s'\n",
+		       str);
+		return 0;
+	}
+	printk(KERN_INFO TAG "setting gcov_persist to %d\n", val);
+	gcov_persist = val;
+
+	return 1;
+}
+__setup("gcov_persist=", gcov_persist_setup);
+
+/* seq_file.start() implementation for gcov data files. Note that the
+ * gcov_iterator interface is designed to be more restrictive than seq_file
+ * (no start from arbitrary position, etc.), to simplify the iterator
+ * implementation. */
+static void *gcov_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	loff_t i;
+
+	gcov_iter_start(seq->private);
+	for (i = 0; i < *pos; i++)
+		if (gcov_iter_next(seq->private))
+			return NULL;
+
+	return seq->private;
+}
+
+/* seq_file.next() implementation for gcov data files. */
+static void *gcov_seq_next(struct seq_file *seq, void *data, loff_t *pos)
+{
+	struct gcov_iterator *iter = data;
+
+	if (gcov_iter_next(iter))
+		return NULL;
+	(*pos)++;
+
+	return iter;
+}
+
+/* seq_file.show() implementation for gcov data files. */
+static int gcov_seq_show(struct seq_file *seq, void *data)
+{
+	struct gcov_iterator *iter = data;
+
+	return gcov_iter_write(iter, seq);
+}
+
+static void gcov_seq_stop(struct seq_file *seq, void *data)
+{
+	/* Unused. */
+}
+
+static struct seq_operations gcov_seq_ops = {
+	.start = gcov_seq_start,
+	.next = gcov_seq_next,
+	.show = gcov_seq_show,
+	.stop = gcov_seq_stop,
+};
+
+/* Return the profiling data set for a given node. This can either be the
+ * original profiling data structure or a duplicate (also called "ghost")
+ * in case the associated object file has been unloaded. */
+static struct gcov_info *get_node_info(struct gcov_node *node)
+{
+	if (node->info)
+		return node->info;
+
+	return node->ghost;
+}
+
+/* open() implementation for gcov data files. Create a copy of the profiling
+ * data set and initialize the iterator and seq_file interface. */
+static int gcov_seq_open(struct inode *inode, struct file *file)
+{
+	struct gcov_node *node = inode->i_private;
+	struct gcov_iterator *iter;
+	struct seq_file *seq;
+	struct gcov_info *info;
+	int rc;
+
+	mutex_lock(&node_lock);
+	/* Read from a profiling data copy to minimize reference tracking
+	 * complexity and concurrent access. */
+	info = gcov_info_dup(get_node_info(node));
+	if (!info) {
+		rc = -ENOMEM;
+		goto out_unlock;
+	}
+	iter = gcov_iter_new(info);
+	if (!iter) {
+		rc = -ENOMEM;
+		goto out_free;
+	}
+	rc = seq_open(file, &gcov_seq_ops);
+	if (rc)
+		goto out_free2;
+	seq = file->private_data;
+	seq->private = iter;
+	goto out_unlock;
+
+out_free2:
+	gcov_iter_free(iter);
+out_free:
+	gcov_info_free(info);
+out_unlock:
+	mutex_unlock(&node_lock);
+
+	return rc;
+}
+
+/* release() implementation for gcov data files. Release resources allocated
+ * by open(). */
+static int gcov_seq_release(struct inode *inode, struct file *file)
+{
+	struct gcov_iterator *iter;
+	struct gcov_info *info;
+	struct seq_file *seq = file->private_data;
+
+	iter = seq->private;
+	info = gcov_iter_get_info(iter);
+	gcov_iter_free(iter);
+	gcov_info_free(info);
+	seq_release(inode, file);
+
+	return 0;
+}
+
+/* Find a node by the associated data file name. Needs to be called with
+ * node_lock held. */
+static struct gcov_node *get_node_by_name(const char *name)
+{
+	struct gcov_node *node;
+	struct gcov_info *info;
+
+	list_for_each_entry(node, &all_head, all) {
+		info = get_node_info(node);
+		if (info && (strcmp(info->filename, name) == 0))
+			return node;
+	}
+
+	return NULL;
+}
+
+static void remove_node(struct gcov_node *node);
+
+/* write() implementation for gcov data files. Reset profiling data for the
+ * associated file. If the object file has been unloaded (i.e. this is
+ * a "ghost" node), remove the debug fs node as well. */
+static ssize_t gcov_seq_write(struct file *file, const char __user *addr,
+			      size_t len, loff_t *pos)
+{
+	struct seq_file *seq = file->private_data;
+	struct gcov_info *info = gcov_iter_get_info(seq->private);
+	struct gcov_node *node;
+
+	mutex_lock(&node_lock);
+	node = get_node_by_name(info->filename);
+	if (node) {
+		/* Reset counts or remove node for unloaded modules. */
+		if (node->ghost)
+			remove_node(node);
+		else
+			gcov_info_reset(node->info);
+	}
+	/* Reset counts for open file. */
+	gcov_info_reset(info);
+	mutex_unlock(&node_lock);
+
+	return len;
+}
+
+/* Given a string <path> representing a file path of format:
+ *   path/to/file.gcda
+ * construct and return a new string:
+ *   <dir/>path/to/file.<ext> */
+static char *link_target(const char *dir, const char *path, const char *ext)
+{
+	char *target;
+	char *old_ext;
+	char *copy;
+
+	copy = kstrdup(path, GFP_KERNEL);
+	if (!copy)
+		return NULL;
+	old_ext = strrchr(copy, '.');
+	if (old_ext)
+		*old_ext = '\0';
+	if (dir)
+		target = kasprintf(GFP_KERNEL, "%s/%s.%s", dir, copy, ext);
+	else
+		target = kasprintf(GFP_KERNEL, "%s.%s", copy, ext);
+	kfree(copy);
+
+	return target;
+}
+
+/* Construct a string representing the symbolic link target for the given
+ * gcov data file name and link type. Depending on the link type and the
+ * location of the data file, the link target can either point to a
+ * subdirectory of srctree, objtree or in an external location. */
+static char *get_link_target(const char *filename, const struct gcov_link *ext)
+{
+	const char *rel;
+	char *result;
+
+	if (strncmp(filename, objtree, strlen(objtree)) == 0) {
+		rel = filename + strlen(objtree) + 1;
+		if (ext->dir == src_tree)
+			result = link_target(srctree, rel, ext->ext);
+		else
+			result = link_target(objtree, rel, ext->ext);
+	} else {
+		/* External compilation. */
+		result = link_target(NULL, filename, ext->ext);
+	}
+
+	return result;
+}
+
+/* Create links to additional files (usually .c and .gcno files) which the
+ * gcov tool expects to find in the same directory as the gcov data file. */
+static void add_links(struct gcov_node *node, struct dentry *parent)
+{
+	char *basename;
+	char *target;
+	int num;
+	int i;
+
+	for (num = 0; gcov_link[num].ext; num++)
+		/* Nothing. */;
+	node->links = kcalloc(num, sizeof(struct dentry *), GFP_KERNEL);
+	if (!node->links)
+		return;
+	for (i = 0; i < num; i++) {
+		target = get_link_target(get_node_info(node)->filename,
+					 &gcov_link[i]);
+		if (!target)
+			goto out_err;
+		basename = strrchr(target, '/');
+		if (!basename)
+			goto out_err;
+		basename++;
+		node->links[i] = debugfs_create_symlink(basename, parent,
+							target);
+		if (!node->links[i])
+			goto out_err;
+		kfree(target);
+	}
+
+	return;
+out_err:
+	kfree(target);
+	while (i-- > 0)
+		debugfs_remove(node->links[i]);
+	kfree(node->links);
+	node->links = NULL;
+}
+
+static struct file_operations gcov_data_fops = {
+	.open = gcov_seq_open,
+	.release = gcov_seq_release,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.write = gcov_seq_write,
+};
+
+/* Basic initialization of a new node. */
+static void init_node(struct gcov_node *node, struct gcov_info *info,
+		      const char *name)
+{
+	INIT_LIST_HEAD(&node->list);
+	INIT_LIST_HEAD(&node->children);
+	INIT_LIST_HEAD(&node->all);
+	node->info = info;
+	if (name)
+		strcpy(node->name, name);
+}
+
+/* Create a new node and associated debugfs entry. Needs to be called with
+ * node_lock held. */
+static struct gcov_node *new_node(struct gcov_node *parent,
+				  struct gcov_info *info, const char *name)
+{
+	struct gcov_node *node;
+
+	node = kzalloc(sizeof(struct gcov_node) + strlen(name) + 1, GFP_KERNEL);
+	if (!node) {
+		printk(KERN_WARNING TAG "out of memory\n");
+		return NULL;
+	}
+	init_node(node, info, name);
+	/* Differentiate between gcov data file nodes and directory nodes. */
+	if (info) {
+		node->dentry = debugfs_create_file(node->name, 0600,
+					parent->dentry, node, &gcov_data_fops);
+	} else
+		node->dentry = debugfs_create_dir(node->name, parent->dentry);
+	if (!node->dentry) {
+		printk(KERN_WARNING TAG "could not create file\n");
+		kfree(node);
+		return NULL;
+	}
+	if (info)
+		add_links(node, parent->dentry);
+	list_add(&node->list, &parent->children);
+	list_add(&node->all, &all_head);
+
+	return node;
+}
+
+/* Remove symbolic links associated with node. */
+static void remove_links(struct gcov_node *node)
+{
+	int i;
+
+	if (!node->links)
+		return;
+	for (i = 0; gcov_link[i].ext; i++)
+		debugfs_remove(node->links[i]);
+	kfree(node->links);
+	node->links = NULL;
+}
+
+/* Remove node from all lists and debugfs and release associated resources.
+ * Needs to be called with node_lock held. */
+static void release_node(struct gcov_node *node)
+{
+	list_del(&node->list);
+	list_del(&node->all);
+	debugfs_remove(node->dentry);
+	remove_links(node);
+	if (node->ghost)
+		gcov_info_free(node->ghost);
+	kfree(node);
+}
+
+/* Release node and empty parents. Needs to be called with node_lock held. */
+static void remove_node(struct gcov_node *node)
+{
+	struct gcov_node *parent;
+
+	while ((node != &root_node) && list_empty(&node->children)) {
+		parent = node->parent;
+		release_node(node);
+		node = parent;
+	}
+}
+
+/* Find child node with given basename. Needs to be called with node_lock
+ * held. */
+static struct gcov_node *get_child_by_name(struct gcov_node *parent,
+					   const char *name)
+{
+	struct gcov_node *node;
+
+	list_for_each_entry(node, &parent->children, list) {
+		if (strcmp(node->name, name) == 0)
+			return node;
+	}
+
+	return NULL;
+}
+
+/* write() implementation for reset file. Reset all profiling data to zero
+ * and remove ghost nodes. */
+static ssize_t reset_write(struct file *file, const char __user *addr,
+			   size_t len, loff_t *pos)
+{
+	struct gcov_node *node;
+	struct gcov_node *r;
+
+	mutex_lock(&node_lock);
+	list_for_each_entry_safe(node, r, &all_head, all) {
+		if (node->info)
+			gcov_info_reset(node->info);
+		else
+			remove_node(node);
+	}
+	mutex_unlock(&node_lock);
+
+	return len;
+}
+
+/* read() implementation for reset file. Unused. */
+static ssize_t reset_read(struct file *file, char __user *addr, size_t len,
+			  loff_t *pos)
+{
+	/* Allow read operation so that a recursive copy won't fail. */
+	return 0;
+}
+
+static struct file_operations gcov_reset_fops = {
+	.write = reset_write,
+	.read = reset_read,
+};
+
+/* Create a node for a given profiling data set and add it to all lists and
+ * debugfs. Needs to be called with node_lock held. */
+static void add_node(struct gcov_info *info)
+{
+	char *filename;
+	char *curr;
+	char *next;
+	struct gcov_node *parent;
+	struct gcov_node *node;
+
+	filename = kstrdup(info->filename, GFP_KERNEL);
+	if (!filename)
+		return;
+	parent = &root_node;
+	/* Create directory nodes along the path. */
+	for (curr = filename; (next = strchr(curr, '/')); curr = next + 1) {
+		if (curr == next)
+			continue;
+		*next = 0;
+		node = get_child_by_name(parent, curr);
+		if (!node) {
+			node = new_node(parent, NULL, curr);
+			if (!node)
+				goto out_err;
+		}
+		parent = node;
+	}
+	/* Create file node. */
+	node = new_node(parent, info, curr);
+	if (node)
+		goto out;
+out_err:
+	remove_node(parent);
+out:
+	kfree(filename);
+}
+
+/* The profiling data set associated with this node is being unloaded. Store a
+ * copy of the profiling data and turn this node into a "ghost". */
+static int ghost_node(struct gcov_node *node)
+{
+	node->ghost = gcov_info_dup(node->info);
+	if (!node->ghost) {
+		printk(KERN_WARNING TAG "could not save data for '%s' (out of "
+		       "memory)\n", node->info->filename);
+		return -ENOMEM;
+	}
+	node->info = NULL;
+
+	return 0;
+}
+
+/* Profiling data for this node has been loaded again. Add profiling data
+ * from previous instantiation and turn this node into a regular node. */
+static void revive_node(struct gcov_node *node, struct gcov_info *info)
+{
+	if (gcov_info_is_compatible(node->ghost, info))
+		gcov_info_add(info, node->ghost);
+	else {
+		printk(KERN_WARNING TAG "could not add data for '%s' "
+		       "(incompatible data)\n", info->filename);
+	}
+	gcov_info_free(node->ghost);
+	node->ghost = NULL;
+	node->info = info;
+}
+
+/* Callback to create/remove profiling files when code compiled with
+ * -fprofile-arcs is loaded/unloaded. */
+void gcov_event(enum gcov_action action, struct gcov_info *info)
+{
+	struct gcov_node *node;
+
+	mutex_lock(&node_lock);
+	node = get_node_by_name(info->filename);
+	switch (action) {
+	case gcov_add:
+		/* Add new node or revive ghost. */
+		if (!node) {
+			add_node(info);
+			break;
+		}
+		if (gcov_persist)
+			revive_node(node, info);
+		else
+			printk(KERN_WARNING TAG "could not add '%s' "
+			       "(already exists)\n", info->filename);
+		break;
+	case gcov_remove:
+		/* Remove node or turn into ghost. */
+		if (!node) {
+			printk(KERN_WARNING TAG "could not remove '%s' (not "
+			       "found)\n", info->filename);
+			break;
+		}
+		if (gcov_persist) {
+			if (!ghost_node(node))
+				break;
+		}
+		remove_node(node);
+		break;
+	}
+	mutex_unlock(&node_lock);
+}
+
+/* Create debugfs entries. */
+static __init int gcov_fs_init(void)
+{
+	int rc;
+
+	init_node(&root_node, NULL, NULL);
+	/* /sys/kernel/debug/gcov will be parent for the reset control file
+	 * and all profiling files. */
+	root_node.dentry = debugfs_create_dir("gcov", NULL);
+	if (!root_node.dentry) {
+		printk(KERN_ERR TAG "could not create root dir\n");
+		rc = -EIO;
+		goto out_remove;
+	}
+	/* Create reset file which resets all profiling counts when written
+	 * to. */
+	reset_dentry = debugfs_create_file("reset", 0600, root_node.dentry,
+					   NULL, &gcov_reset_fops);
+	if (!reset_dentry) {
+		printk(KERN_ERR TAG "could not create reset file\n");
+		rc = -EIO;
+		goto out_remove;
+	}
+	/* Replay previous events to get our fs hierarchy up-to-date. */
+	gcov_enable_events();
+
+	return 0;
+out_remove:
+	if (root_node.dentry)
+		debugfs_remove(root_node.dentry);
+
+	return rc;
+}
+__initcall(gcov_fs_init);
Index: linux-2.6.26-rc3/kernel/gcov/gcc_3_4.c
===================================================================
--- /dev/null
+++ linux-2.6.26-rc3/kernel/gcov/gcc_3_4.c
@@ -0,0 +1,420 @@
+/*
+ *  This code provides functions to handle gcc's profiling data format
+ *  introduced with gcc 3.4. Future versions of gcc may change the gcov
+ *  format (as happened before), so all format-specific information needs
+ *  to be kept modular and easily exchangeable.
+ *
+ *  This file is based on gcc-internal definitions. Functions and data
+ *  structures are defined to be compatible with gcc counterparts.
+ *  For a better understanding, refer to gcc source: gcc/gcov-io.h.
+ *
+ *    Copyright IBM Corp. 2008
+ *    Author(s): Peter Oberparleiter <peter.oberparleiter@xxxxxxxxxx>
+ *
+ *    Uses gcc-internal data definitions.
+ */
+
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/seq_file.h>
+#include "gcov.h"
+
+/* Symbolic links to be created for each profiling data file. */
+const struct gcov_link gcov_link[] = {
+	{ src_tree, "c" },	/* Link to .c file in $(srctree). */
+	{ obj_tree, "gcno" },	/* Link to .gcno file in $(objtree). */
+	{ 0, NULL},
+};
+
+/* Determine whether a counter is active. Based on gcc magic. Doesn't change
+ * at run-time. */
+static int counter_active(struct gcov_info *info, unsigned int type)
+{
+	return (1 << type) & info->ctr_mask;
+}
+
+/* Determine number of active counters. Based on gcc magic. */
+static unsigned int num_counter_active(struct gcov_info *info)
+{
+	unsigned int i;
+	unsigned int result = 0;
+
+	for (i = 0; i < GCOV_COUNTERS; i++)
+		if (counter_active(info, i))
+			result++;
+	return result;
+}
+
+/**
+ * gcov_info_reset - reset profiling data to zero
+ * @info: profiling data set
+ */
+void gcov_info_reset(struct gcov_info *info)
+{
+	unsigned int active = num_counter_active(info);
+	unsigned int i;
+
+	for (i = 0; i < active; i++)
+		memset(info->counts[i].values, 0,
+		       info->counts[i].num * sizeof(gcov_type));
+}
+
+/**
+ * gcov_info_is_compatible - check if profiling data can be added
+ * @info1: first profiling data set
+ * @info2: second profiling data set
+ *
+ * Returns non-zero if profiling data can be added, zero otherwise.
+ */
+int gcov_info_is_compatible(struct gcov_info *info1, struct gcov_info *info2)
+{
+	return (info1->stamp == info2->stamp);
+}
+
+/**
+ * gcov_info_add - add up profiling data
+ * @dest: profiling data set to which data is added
+ * @source: profiling data set which is added
+ *
+ * Adds profiling counts of @source to @dest.
+ */
+void gcov_info_add(struct gcov_info *dest, struct gcov_info *source)
+{
+	unsigned int i;
+	unsigned int j;
+
+	for (i = 0; i < num_counter_active(dest); i++)
+		for (j = 0; j < dest->counts[i].num; j++)
+			dest->counts[i].values[j] +=
+				source->counts[i].values[j];
+}
+
+/* Get size of function info entry. Based on gcc magic. */
+static size_t get_fn_size(struct gcov_info *info)
+{
+	size_t size;
+
+	size = sizeof(struct gcov_fn_info) + num_counter_active(info) *
+	       sizeof(unsigned int);
+	if (__alignof__(struct gcov_fn_info) > sizeof(unsigned int))
+		size = ALIGN(size, __alignof__(struct gcov_fn_info));
+	return size;
+}
+
+/* Get address of function info entry. Based on gcc magic. */
+static struct gcov_fn_info *get_fn_info(struct gcov_info *info, unsigned int fn)
+{
+	return (struct gcov_fn_info *)
+		((char *) info->functions + fn * get_fn_size(info));
+}
+
+/**
+ * gcov_info_dup - duplicate profiling data set
+ * @info: profiling data set to duplicate
+ *
+ * Return newly allocated duplicate on success, %NULL on error.
+ */
+struct gcov_info *gcov_info_dup(struct gcov_info *info)
+{
+	struct gcov_info *dup;
+	unsigned int i;
+	unsigned int active = num_counter_active(info);
+
+	/* Duplicate gcov_info. */
+	dup = kzalloc(sizeof(struct gcov_info) +
+		      sizeof(struct gcov_ctr_info) * active, GFP_KERNEL);
+	if (!dup)
+		return NULL;
+	dup->version = info->version;
+	dup->stamp = info->stamp;
+	dup->n_functions = info->n_functions;
+	dup->ctr_mask = info->ctr_mask;
+	/* Duplicate filename. */
+	dup->filename = kstrdup(info->filename, GFP_KERNEL);
+	if (!dup->filename)
+		goto out_free;
+	/* Duplicate table of functions. */
+	dup->functions = kmemdup(info->functions, info->n_functions *
+				 get_fn_size(info), GFP_KERNEL);
+	if (!dup->functions)
+		goto out_free;
+	/* Duplicate counter arrays. */
+	for (i = 0; i < active ; i++) {
+		dup->counts[i].num = info->counts[i].num;
+		dup->counts[i].merge = info->counts[i].merge;
+		dup->counts[i].values = kmemdup(info->counts[i].values,
+			sizeof(gcov_type) * info->counts[i].num,
+			GFP_KERNEL);
+		if (!dup->counts[i].values)
+			goto out_free;
+	}
+	return dup;
+
+out_free:
+	gcov_info_free(dup);
+
+	return NULL;
+}
+
+/**
+ * gcov_info_free - release memory for profiling data set duplicate
+ * @info: profiling data set duplicate to free
+ */
+void gcov_info_free(struct gcov_info *info)
+{
+	unsigned int active = num_counter_active(info);
+	unsigned int i;
+
+	for (i = 0; i < active ; i++)
+		kfree(info->counts[i].values);
+	kfree(info->functions);
+	kfree(info->filename);
+	kfree(info);
+}
+
+/**
+ * struct type_info - iterator helper array
+ * @ctr_type: counter type
+ * @offset: index of the first value of the current function for this type
+ *
+ * This array is needed to convert the in-memory data format into the in-file
+ * data format:
+ *
+ * In-memory:
+ *   for each counter type
+ *     for each function
+ *       values
+ *
+ * In-file:
+ *   for each function
+ *     for each counter type
+ *       values
+ *
+ * See gcc source gcc/gcov-io.h for more information on data organization.
+ */
+struct type_info {
+	int ctr_type;
+	unsigned int offset;
+};
+
+/**
+ * struct gcov_iterator - specifies current file position in logical records
+ * @info: associated profiling data
+ * @record: record type
+ * @function: function number
+ * @type: counter type
+ * @count: index into values array
+ * @num_types: number of counter types
+ * @type_info: helper array to get values-array offset for current function
+ */
+struct gcov_iterator {
+	struct gcov_info *info;
+
+	int record;
+	unsigned int function;
+	unsigned int type;
+	unsigned int count;
+
+	int num_types;
+	struct type_info type_info[0];
+};
+
+static struct gcov_fn_info *get_func(struct gcov_iterator *iter)
+{
+	return get_fn_info(iter->info, iter->function);
+}
+
+static struct type_info *get_type(struct gcov_iterator *iter)
+{
+	return &iter->type_info[iter->type];
+}
+
+/**
+ * gcov_iter_new - allocate and initialize profiling data iterator
+ * @info: profiling data set to be iterated
+ *
+ * Return file iterator on success, %NULL otherwise.
+ */
+struct gcov_iterator *gcov_iter_new(struct gcov_info *info)
+{
+	struct gcov_iterator *iter;
+
+	iter = kzalloc(sizeof(struct gcov_iterator) +
+		       num_counter_active(info) * sizeof(struct type_info),
+		       GFP_KERNEL);
+	if (iter)
+		iter->info = info;
+
+	return iter;
+}
+
+/**
+ * gcov_iter_free - release memory for iterator
+ * @iter: file iterator to free
+ */
+void gcov_iter_free(struct gcov_iterator *iter)
+{
+	kfree(iter);
+}
+
+/**
+ * gcov_iter_get_info - return profiling data set for given file iterator
+ * @iter: file iterator
+ */
+struct gcov_info *gcov_iter_get_info(struct gcov_iterator *iter)
+{
+	return iter->info;
+}
+
+/**
+ * gcov_iter_start - reset file iterator to starting position
+ * @iter: file iterator
+ */
+void gcov_iter_start(struct gcov_iterator *iter)
+{
+	int i;
+
+	iter->record = 0;
+	iter->function = 0;
+	iter->type = 0;
+	iter->count = 0;
+	iter->num_types = 0;
+	for (i = 0; i < GCOV_COUNTERS; i++) {
+		if (counter_active(iter->info, i)) {
+			iter->type_info[iter->num_types].ctr_type = i;
+			iter->type_info[iter->num_types++].offset = 0;
+		}
+	}
+}
+
+/**
+ * gcov_iter_next - advance file iterator to next logical record
+ * @iter: file iterator
+ *
+ * Return zero if new position is valid, non-zero if iterator has reached end.
+ */
+int gcov_iter_next(struct gcov_iterator *iter)
+{
+	switch (iter->record) {
+	case 0:
+	case 1:
+	case 3:
+	case 4:
+	case 5:
+	case 7:
+		/* Advance to next record */
+		iter->record++;
+		break;
+	case 9:
+		/* Advance to next count */
+		iter->count++;
+		/* fall through */
+	case 8:
+		if (iter->count < get_func(iter)->n_ctrs[iter->type]) {
+			iter->record = 9;
+			break;
+		}
+		/* Advance to next counter type */
+		get_type(iter)->offset += iter->count;
+		iter->count = 0;
+		iter->type++;
+		/* fall through */
+	case 6:
+		if (iter->type < iter->num_types) {
+			iter->record = 7;
+			break;
+		}
+		/* Advance to next function */
+		iter->type = 0;
+		iter->function++;
+		/* fall through */
+	case 2:
+		if (iter->function < iter->info->n_functions)
+			iter->record = 3;
+		else
+			iter->record = -1;
+		break;
+	}
+	/* Check for EOF. */
+	if (iter->record == -1)
+		return -EINVAL;
+	else
+		return 0;
+}
+
+/**
+ * seq_write_gcov_int - write number in gcov format to seq_file
+ * @seq: seq_file handle
+ * @size: size of number in bytes (either 4 or 8)
+ * @v: value to be stored
+ *
+ * Number format defined by gcc: numbers are recorded in the 32 bit
+ * unsigned binary form of the endianness of the machine generating the
+ * file. 64 bit numbers are stored as two 32 bit numbers, the low part
+ * first.
+ */
+static int seq_write_gcov_int(struct seq_file *seq, size_t size, u64 v)
+{
+	u32 data[2];
+
+	switch (size) {
+	case 8:
+		data[1] = (v >> 32);
+		/* fall through */
+	case 4:
+		data[0] = (v & 0xffffffffUL);
+		return seq_write(seq, data, size);
+	}
+	return -EINVAL;
+}
+
+/**
+ * gcov_iter_write - write data for current pos to seq_file
+ * @iter: file iterator
+ * @seq: seq_file handle
+ *
+ * Return zero on success, non-zero otherwise.
+ */
+int gcov_iter_write(struct gcov_iterator *iter, struct seq_file *seq)
+{
+	int rc = -EINVAL;
+
+	switch (iter->record) {
+	case 0: /* file magic */
+		rc = seq_write_gcov_int(seq, 4, GCOV_DATA_MAGIC);
+		break;
+	case 1: /* gcov_version */
+		rc = seq_write_gcov_int(seq, 4, iter->info->version);
+		break;
+	case 2: /* time stamp */
+		rc = seq_write_gcov_int(seq, 4, iter->info->stamp);
+		break;
+	case 3: /* function tag */
+		rc = seq_write_gcov_int(seq, 4, GCOV_TAG_FUNCTION);
+		break;
+	case 4: /* function tag length */
+		rc = seq_write_gcov_int(seq, 4, 2);
+		break;
+	case 5: /* function ident*/
+		rc = seq_write_gcov_int(seq, 4, get_func(iter)->ident);
+		break;
+	case 6: /* function checksum */
+		rc = seq_write_gcov_int(seq, 4, get_func(iter)->checksum);
+		break;
+	case 7: /* count tag */
+		rc = seq_write_gcov_int(seq, 4,
+			GCOV_TAG_FOR_COUNTER(get_type(iter)->ctr_type));
+		break;
+	case 8: /* count length */
+		rc = seq_write_gcov_int(seq, 4,
+				get_func(iter)->n_ctrs[iter->type] * 2);
+		break;
+	case 9: /* count */
+		rc = seq_write_gcov_int(seq, 8,
+			iter->info->counts[iter->type].
+				values[iter->count + get_type(iter)->offset]);
+		break;
+	}
+	return rc;
+}
Index: linux-2.6.26-rc3/init/main.c
===================================================================
--- linux-2.6.26-rc3.orig/init/main.c
+++ linux-2.6.26-rc3/init/main.c
@@ -80,6 +80,14 @@
 #warning gcc-4.1.0 is known to miscompile the kernel.  A different compiler version is recommended.
 #endif
 
+#ifdef CONFIG_GCOV_PROFILE
+
+#if GCC_VERSION_LOWER(3, 4)
+#error "GCOV profiling support for gcc versions below 3.4 not included"
+#endif /* GCC_VERSION_LOWER */
+
+#endif /* CONFIG_GCOV_PROFILE */
+
 static int kernel_init(void *);
 
 extern void init_IRQ(void);
Index: linux-2.6.26-rc3/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.26-rc3.orig/Documentation/kernel-parameters.txt
+++ linux-2.6.26-rc3/Documentation/kernel-parameters.txt
@@ -42,6 +42,7 @@ parameter is applicable:
 	EFI	EFI Partitioning (GPT) is enabled
 	EIDE	EIDE/ATAPI support is enabled.
 	FB	The frame buffer device is enabled.
+	GCOV	GCOV profiling is enabled.
 	HW	Appropriate hardware is enabled.
 	IA-64	IA-64 architecture is enabled.
 	IOSCHED	More than one I/O scheduler is enabled.
@@ -704,6 +705,12 @@ and is between 256 and 4096 characters. 
 			Format: off | on
 			default: on
 
+	gcov_persist=	[GCOV] When non-zero (default), profiling data for
+			kernel modules is saved and remains accessible via
+			debugfs, even when the module is unloaded/reloaded.
+			When zero, profiling data is discarded and associated
+			debugfs files are removed at module unload time.
+
 	gdth=		[HW,SCSI]
 			See header of drivers/scsi/gdth.c.
 
Index: linux-2.6.26-rc3/Documentation/gcov.txt
===================================================================
--- /dev/null
+++ linux-2.6.26-rc3/Documentation/gcov.txt
@@ -0,0 +1,127 @@
+Using gcov with the Linux kernel
+================================
+
+1. Introduction
+2. Preparation
+3. Customization
+4. Files
+5. Modules
+
+
+1. Introduction
+===============
+
+gcov profiling kernel support enables the use of GCC's coverage testing
+tool gcov [1] with the Linux kernel. Coverage data of a running kernel
+is exported in gcov-compatible format via the "gcov "debugfs directory.
+To get coverage data for a specific file, simply use gcov with the -o
+option while running as root:
+
+# gcov -o /sys/kernel/debug/gcov/tmp/linux/kernel spinlock.c
+
+This will create source code files annotated with execution counts
+in the current directory. In addition, graphical gcov front-ends such
+as lcov [2] can be used to automate the process of collecting data
+for the entire kernel and provide coverage overviews in HTML format.
+
+Possible uses:
+
+* debugging (has this line been executed at all?)
+* test improvement (how do I change my test to cover these lines?)
+* minimizing kernel configurations (do I need this option if the
+  associated code is never executed?)
+
+
+2. Preparation
+==============
+
+Configure the kernel with:
+
+        CONFIG_DEBUGFS=y
+        CONFIG_GCOV_PROFILE=y
+
+To get coverage data for the entire kernel:
+
+        CONFIG_GCOV_PROFILE_ALL=y
+
+Note that kernels compiled with profiling flags will be significantly
+larger and run slower.
+
+Profiling data will only become accessible once debugfs has been
+mounted:
+
+        mount -t debugfs none /sys/kernel/debug
+
+
+3. Customization
+================
+
+To enable profiling for specific files or directories, add a line
+similar to the following to the respective kernel Makefile:
+
+        For a single file (e.g. main.o):
+                GCOV_main.o := y
+
+        For all files in one directory:
+                GCOV := y
+
+        To exclude files from being profiled even when
+        CONFIG_GCOV_PROFILE_ALL is specified, use:
+
+                GCOV_main.o := n
+        and:
+                GCOV := n
+
+Only files which are linked to the main kernel image or are compiled as
+kernel modules are supported by this mechanism.
+
+
+4. Files
+========
+
+The gcov kernel support creates the following files in debugfs:
+
+        /sys/kernel/debug/gcov
+                Parent directory for all gcov-related files.
+
+        /sys/kernel/debug/gcov/reset
+                Global reset file: resets all coverage data to zero when
+                written to.
+
+        /sys/kernel/debug/gcov/path/to/compile/dir/file.gcda
+                The actual gcov data file as understood by the gcov
+                tool. Resets file coverage data to zero when written to.
+
+        /sys/kernel/debug/gcov/path/to/compile/dir/file.gcno
+                Symbolic link to a static data file required by the gcov
+                tool. This file is generated by gcc when compiling with
+                option -ftest-coverage.
+
+        /sys/kernel/debug/gcov/path/to/compile/dir/file.c
+                Symbolic link to the source code as required by the gcov
+                tool.
+
+
+5. Modules
+==========
+
+Kernel modules may contain cleanup code which is only executed during
+module unload time. The gcov mechanism provides a means to collect
+coverage data for such code by keeping a copy of the data associated
+with the unloaded module. This data remains available through debugfs.
+Once the module is loaded again, the associated coverage counters are
+initialized with the data from its previous instantiation.
+
+This behavior can be deactivated by specifying the gcov_persist kernel
+parameter:
+
+        gcov_persist=0
+
+At run-time, a user can also choose to discard data for an unloaded
+module by writing to its data file or the global reset file.
+
+
+--
+
+[1] http://gcc.gnu.org/onlinedocs/gcc/Gcov.html
+[2] http://ltp.sourceforge.net/coverage/lcov.php
Index: linux-2.6.26-rc3/arch/Kconfig
===================================================================
--- linux-2.6.26-rc3.orig/arch/Kconfig
+++ linux-2.6.26-rc3/arch/Kconfig
@@ -39,3 +39,5 @@ config HAVE_KRETPROBES
 
 config HAVE_DMA_ATTRS
 	def_bool n
+
+source "kernel/gcov/Kconfig"



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