gcov: add gcov profiling infrastructure

Enable the use of GCC's coverage testing tool gcov [1] with the Linux
kernel.  gcov may be useful for:

 * debugging (has this code been reached 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 run?)

The profiling patch incorporates the following changes:

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

Note that on some architectures, enabling gcc's profiling option
"-fprofile-arcs" for the entire kernel may trigger compile/link/
run-time problems, some of which are caused by toolchain bugs and
others which require adjustment of architecture code.

For this reason profiling the entire kernel is initially restricted
to those architectures for which it is known to work without changes.
This restriction can be lifted once an architecture has been tested
and found compatible with gcc's profiling. Profiling of single files
or directories is still available on all platforms (see config help
text).

[1] http://gcc.gnu.org/onlinedocs/gcc/Gcov.html

Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Li Wei <W.Li@Sun.COM>
Cc: Michael Ellerman <michaele@au1.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Heiko Carstens <heicars2@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <mschwid2@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 148 insertions, 0 deletions

diff --git a/kernel/gcov/base.c b/kernel/gcov/base.c
new file mode 100644
index 000000000000..9b22d03cc581
--- /dev/null
+++ b/kernel/gcov/base.c
@@ -0,0 +1,148 @@
+/*
+ *  This code maintains a list of active profiling data structures.
+ *
+ *    Copyright IBM Corp. 2009
+ *    Author(s): Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
+ *
+ *    Uses gcc-internal data definitions.
+ *    Based on the gcov-kernel patch by:
+ *               Hubertus Franke <frankeh@us.ibm.com>
+ *               Nigel Hinds <nhinds@us.ibm.com>
+ *               Rajan Ravindran <rajancr@us.ibm.com>
+ *               Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
+ *               Paul Larson
+ */
+
+#define pr_fmt(fmt)     "gcov: " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mutex.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.
+                 */
+                pr_info("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);
+
+/**
+ * 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);
+}
+
+#ifdef CONFIG_MODULES
+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)
+{
+        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);
+
+        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);
+}
+device_initcall(gcov_init);
+#endif /* CONFIG_MODULES */