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Message-ID: <4843F6E1.3040007@de.ibm.com>
Date: Mon, 02 Jun 2008 15:34:25 +0200
From: Peter Oberparleiter <peter.oberparleiter@...ibm.com>
To: linux-kernel@...r.kernel.org
CC: ltp-coverage@...ts.sourceforge.net,
Andrew Morton <akpm@...ux-foundation.org>,
Sam Ravnborg <sam@...nborg.org>,
Peter Oberparleiter <oberparleiter@...glemail.com>
Subject: [PATCH 4/6] gcov: add gcov profiling infrastructure
From: Peter Oberparleiter <peter.oberparleiter@...ibm.com>
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@...ibm.com>
---
Documentation/gcov.txt | 136 +++++++
Documentation/kernel-parameters.txt | 7
Makefile | 10
arch/Kconfig | 2
init/main.c | 8
kernel/Makefile | 1
kernel/gcov/Kconfig | 45 ++
kernel/gcov/Makefile | 1
kernel/gcov/base.c | 145 +++++++
kernel/gcov/fs.c | 501 ++++++++++++++++++++++++++
kernel/gcov/gcc_3_4.c | 413 +++++++++++++++++++++
kernel/gcov/gcov.h | 119 ++++++
scripts/Makefile.lib | 8
13 files changed, 1392 insertions(+), 4 deletions(-)
Index: linux-2.6.26-rc4/Makefile
===================================================================
--- linux-2.6.26-rc4.orig/Makefile
+++ linux-2.6.26-rc4/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
@@ -1133,7 +1134,8 @@ 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
@@ -1337,8 +1339,8 @@ 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-rc4/scripts/Makefile.lib
===================================================================
--- linux-2.6.26-rc4.orig/scripts/Makefile.lib
+++ linux-2.6.26-rc4/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-rc4/kernel/gcov/Kconfig
===================================================================
--- /dev/null
+++ linux-2.6.26-rc4/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-rc4/kernel/gcov/base.c
===================================================================
--- /dev/null
+++ linux-2.6.26-rc4/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@...ibm.com>
+ *
+ * Uses gcc-internal data definitions.
+ * Based on the gcov-kernel patch by:
+ * Hubertus Franke <frankeh@...ibm.com>
+ * Nigel Hinds <nhinds@...ibm.com>
+ * Rajan Ravindran <rajancr@...ibm.com>
+ * Peter Oberparleiter <peter.oberparleiter@...ibm.com>
+ * 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-rc4/kernel/gcov/gcov.h
===================================================================
--- /dev/null
+++ linux-2.6.26-rc4/kernel/gcov/gcov.h
@@ -0,0 +1,119 @@
+/*
+ * 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@...ibm.com>
+ *
+ * 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);
+
+#endif /* GCOV_H */
Index: linux-2.6.26-rc4/kernel/Makefile
===================================================================
--- linux-2.6.26-rc4.orig/kernel/Makefile
+++ linux-2.6.26-rc4/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@...uxcare.com.au>, the -fno-omit-frame-pointer is
Index: linux-2.6.26-rc4/kernel/gcov/Makefile
===================================================================
--- /dev/null
+++ linux-2.6.26-rc4/kernel/gcov/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_GCOV_PROFILE) := base.o fs.o gcc_3_4.o
Index: linux-2.6.26-rc4/kernel/gcov/fs.c
===================================================================
--- /dev/null
+++ linux-2.6.26-rc4/kernel/gcov/fs.c
@@ -0,0 +1,501 @@
+/*
+ * This code exports profiling data as debugfs files to userspace.
+ *
+ * Copyright IBM Corp. 2008
+ * Author(s): Peter Oberparleiter <peter.oberparleiter@...ibm.com>
+ *
+ * Uses gcc-internal data definitions.
+ * Based on the gcov-kernel patch by:
+ * Hubertus Franke <frankeh@...ibm.com>
+ * Nigel Hinds <nhinds@...ibm.com>
+ * Rajan Ravindran <rajancr@...ibm.com>
+ * Peter Oberparleiter <peter.oberparleiter@...ibm.com>
+ * 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
+ * @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.
+ */
+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;
+ char name[0];
+};
+
+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;
+}
+
+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;
+ }
+ list_add(&node->list, &parent->children);
+ list_add(&node->all, &all_head);
+
+ return node;
+}
+
+/* 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);
+ 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 "discarding saved data for '%s' "
+ "(version changed)\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-rc4/kernel/gcov/gcc_3_4.c
===================================================================
--- /dev/null
+++ linux-2.6.26-rc4/kernel/gcov/gcc_3_4.c
@@ -0,0 +1,413 @@
+/*
+ * 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@...ibm.com>
+ *
+ * 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"
+
+/* 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-rc4/init/main.c
===================================================================
--- linux-2.6.26-rc4.orig/init/main.c
+++ linux-2.6.26-rc4/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-rc4/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.26-rc4.orig/Documentation/kernel-parameters.txt
+++ linux-2.6.26-rc4/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-rc4/Documentation/gcov.txt
===================================================================
--- /dev/null
+++ linux-2.6.26-rc4/Documentation/gcov.txt
@@ -0,0 +1,136 @@
+Using gcov with the Linux kernel
+================================
+
+1. Introduction
+2. Preparation
+3. Customization
+4. Files
+5. Modules
+6. Troubleshooting
+
+
+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.
+
+Example:
+
+To get coverage data for file base.c in directory drivers/base, simply
+change to the kernel build directory and run gcov with the -o option
+(assumptions: kernel was built in /tmp/linux and debugfs is mounted at
+/sys/kernel/debug):
+
+# cd /tmp/linux
+# gcov -o drivers/base/ bus.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.
+
+
+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.
+
+
+6. Troubleshooting
+==================
+
+Problem: Compilation aborts during linker step.
+Cause: Profiling flags are specified for source files which are not
+ linked to the main kernel or which are linked by a custom
+ linker procedure.
+Solution: Exclude affected source files from profiling by specifying
+ GCOV := n in the corresponding Makefile.
+
+
+--
+
+[1] http://gcc.gnu.org/onlinedocs/gcc/Gcov.html
+[2] http://ltp.sourceforge.net/coverage/lcov.php
Index: linux-2.6.26-rc4/arch/Kconfig
===================================================================
--- linux-2.6.26-rc4.orig/arch/Kconfig
+++ linux-2.6.26-rc4/arch/Kconfig
@@ -39,3 +39,5 @@ config HAVE_KRETPROBES
config HAVE_DMA_ATTRS
def_bool n
+
+source "kernel/gcov/Kconfig"
--
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