---

yaml
---
r: 100425
b: refs/heads/master
c: 3d08339
h: refs/heads/master
i:
  100423: e9279be
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 6cd8a4bb2f97527a9ceb30bc77ea4e959c6a95e3
+refs/heads/master: 3d0833953e1b98b79ddf491dd49229eef9baeac1

trunk/arch/x86/kernel/Makefile

@@ -56,6 +56,7 @@ obj-$(CONFIG_X86_MPPARSE)	+= mpparse.o
 obj-$(CONFIG_X86_LOCAL_APIC)	+= apic_$(BITS).o nmi_$(BITS).o
 obj-$(CONFIG_X86_IO_APIC)	+= io_apic_$(BITS).o
 obj-$(CONFIG_X86_REBOOTFIXUPS)	+= reboot_fixups_32.o
+obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o
 obj-$(CONFIG_KEXEC)		+= machine_kexec_$(BITS).o
 obj-$(CONFIG_KEXEC)		+= relocate_kernel_$(BITS).o crash.o
 obj-$(CONFIG_CRASH_DUMP)	+= crash_dump_$(BITS).o

trunk/arch/x86/kernel/ftrace.c

@@ -0,0 +1,237 @@
+/*
+ * Code for replacing ftrace calls with jumps.
+ *
+ * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
+ *
+ * Thanks goes to Ingo Molnar, for suggesting the idea.
+ * Mathieu Desnoyers, for suggesting postponing the modifications.
+ * Arjan van de Ven, for keeping me straight, and explaining to me
+ * the dangers of modifying code on the run.
+ */
+
+#include <linux/spinlock.h>
+#include <linux/hardirq.h>
+#include <linux/ftrace.h>
+#include <linux/percpu.h>
+#include <linux/init.h>
+#include <linux/list.h>
+
+#define CALL_BACK		5
+
+#define JMPFWD			0x03eb
+
+static unsigned short ftrace_jmp = JMPFWD;
+
+struct ftrace_record {
+	struct dyn_ftrace	rec;
+	int			failed;
+} __attribute__((packed));
+
+struct ftrace_page {
+	struct ftrace_page	*next;
+	int			index;
+	struct ftrace_record	records[];
+} __attribute__((packed));
+
+#define ENTRIES_PER_PAGE \
+  ((PAGE_SIZE - sizeof(struct ftrace_page)) / sizeof(struct ftrace_record))
+
+/* estimate from running different kernels */
+#define NR_TO_INIT		10000
+
+#define MCOUNT_ADDR ((long)(&mcount))
+
+union ftrace_code_union {
+	char code[5];
+	struct {
+		char e8;
+		int offset;
+	} __attribute__((packed));
+};
+
+static struct ftrace_page	*ftrace_pages_start;
+static struct ftrace_page	*ftrace_pages;
+
+notrace struct dyn_ftrace *ftrace_alloc_shutdown_node(unsigned long ip)
+{
+	struct ftrace_record *rec;
+	unsigned short save;
+
+	ip -= CALL_BACK;
+	save = *(short *)ip;
+
+	/* If this was already converted, skip it */
+	if (save == JMPFWD)
+		return NULL;
+
+	if (ftrace_pages->index == ENTRIES_PER_PAGE) {
+		if (!ftrace_pages->next)
+			return NULL;
+		ftrace_pages = ftrace_pages->next;
+	}
+
+	rec = &ftrace_pages->records[ftrace_pages->index++];
+
+	return &rec->rec;
+}
+
+static int notrace
+ftrace_modify_code(unsigned long ip, unsigned char *old_code,
+		   unsigned char *new_code)
+{
+	unsigned short old = *(unsigned short *)old_code;
+	unsigned short new = *(unsigned short *)new_code;
+	unsigned short replaced;
+	int faulted = 0;
+
+	/*
+	 * Note: Due to modules and __init, code can
+	 *  disappear and change, we need to protect against faulting
+	 *  as well as code changing.
+	 *
+	 * No real locking needed, this code is run through
+	 * kstop_machine.
+	 */
+	asm volatile (
+		"1: lock\n"
+		"   cmpxchg %w3, (%2)\n"
+		"2:\n"
+		".section .fixup, \"ax\"\n"
+		"	movl $1, %0\n"
+		"3:	jmp 2b\n"
+		".previous\n"
+		_ASM_EXTABLE(1b, 3b)
+		: "=r"(faulted), "=a"(replaced)
+		: "r"(ip), "r"(new), "0"(faulted), "a"(old)
+		: "memory");
+	sync_core();
+
+	if (replaced != old)
+		faulted = 2;
+
+	return faulted;
+}
+
+static int notrace ftrace_calc_offset(long ip)
+{
+	return (int)(MCOUNT_ADDR - ip);
+}
+
+notrace void ftrace_code_disable(struct dyn_ftrace *rec)
+{
+	unsigned long ip;
+	union ftrace_code_union save;
+	struct ftrace_record *r =
+		container_of(rec, struct ftrace_record, rec);
+
+	ip = rec->ip;
+
+	save.e8		= 0xe8;
+	save.offset 	= ftrace_calc_offset(ip);
+
+	/* move the IP back to the start of the call */
+	ip -= CALL_BACK;
+
+	r->failed = ftrace_modify_code(ip, save.code, (char *)&ftrace_jmp);
+}
+
+static void notrace ftrace_replace_code(int saved)
+{
+	unsigned char *new = NULL, *old = NULL;
+	struct ftrace_record *rec;
+	struct ftrace_page *pg;
+	unsigned long ip;
+	int i;
+
+	if (saved)
+		old = (char *)&ftrace_jmp;
+	else
+		new = (char *)&ftrace_jmp;
+
+	for (pg = ftrace_pages_start; pg; pg = pg->next) {
+		for (i = 0; i < pg->index; i++) {
+			union ftrace_code_union calc;
+			rec = &pg->records[i];
+
+			/* don't modify code that has already faulted */
+			if (rec->failed)
+				continue;
+
+			ip = rec->rec.ip;
+
+			calc.e8		= 0xe8;
+			calc.offset	= ftrace_calc_offset(ip);
+
+			if (saved)
+				new = calc.code;
+			else
+				old = calc.code;
+
+			ip -= CALL_BACK;
+
+			rec->failed = ftrace_modify_code(ip, old, new);
+		}
+	}
+
+}
+
+notrace void ftrace_startup_code(void)
+{
+	ftrace_replace_code(1);
+}
+
+notrace void ftrace_shutdown_code(void)
+{
+	ftrace_replace_code(0);
+}
+
+notrace void ftrace_shutdown_replenish(void)
+{
+	if (ftrace_pages->next)
+		return;
+
+	/* allocate another page */
+	ftrace_pages->next = (void *)get_zeroed_page(GFP_KERNEL);
+}
+
+notrace int ftrace_shutdown_arch_init(void)
+{
+	struct ftrace_page *pg;
+	int cnt;
+	int i;
+
+	/* allocate a few pages */
+	ftrace_pages_start = (void *)get_zeroed_page(GFP_KERNEL);
+	if (!ftrace_pages_start)
+		return -1;
+
+	/*
+	 * Allocate a few more pages.
+	 *
+	 * TODO: have some parser search vmlinux before
+	 *   final linking to find all calls to ftrace.
+	 *   Then we can:
+	 *    a) know how many pages to allocate.
+	 *     and/or
+	 *    b) set up the table then.
+	 *
+	 *  The dynamic code is still necessary for
+	 *  modules.
+	 */
+
+	pg = ftrace_pages = ftrace_pages_start;
+
+	cnt = NR_TO_INIT / ENTRIES_PER_PAGE;
+
+	for (i = 0; i < cnt; i++) {
+		pg->next = (void *)get_zeroed_page(GFP_KERNEL);
+
+		/* If we fail, we'll try later anyway */
+		if (!pg->next)
+			break;
+
+		pg = pg->next;
+	}
+
+	return 0;
+}

trunk/include/linux/ftrace.h

@@ -32,6 +32,24 @@ extern void mcount(void);
 # define clear_ftrace_function(ops) do { } while (0)
 #endif /* CONFIG_FTRACE */
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+# define FTRACE_HASHBITS	10
+# define FTRACE_HASHSIZE	(1<<FTRACE_HASHBITS)
+
+struct dyn_ftrace {
+	struct hlist_node node;
+	unsigned long	  ip;
+};
+
+/* defined in arch */
+extern struct dyn_ftrace *
+ftrace_alloc_shutdown_node(unsigned long ip);
+extern int ftrace_shutdown_arch_init(void);
+extern void ftrace_code_disable(struct dyn_ftrace *rec);
+extern void ftrace_startup_code(void);
+extern void ftrace_shutdown_code(void);
+extern void ftrace_shutdown_replenish(void);
+#endif
 
 #ifdef CONFIG_FRAME_POINTER
 /* TODO: need to fix this for ARM */

trunk/kernel/trace/Kconfig

@@ -88,3 +88,20 @@ config CONTEXT_SWITCH_TRACER
 	  This tracer gets called from the context switch and records
 	  all switching of tasks.
 
+config DYNAMIC_FTRACE
+	bool "enable/disable ftrace tracepoints dynamically"
+	depends on FTRACE
+	default y
+	help
+         This option will modify all the calls to ftrace dynamically
+	 (will patch them out of the binary image and replaces them
+	 with a No-Op instruction) as they are called. A table is
+	 created to dynamically enable them again.
+
+	 This way a CONFIG_FTRACE kernel is slightly larger, but otherwise
+	 has native performance as long as no tracing is active.
+
+	 The changes to the code are done by a kernel thread that
+	 wakes up once a second and checks to see if any ftrace calls
+	 were made. If so, it runs stop_machine (stops all CPUS)
+	 and modifies the code to jump over the call to ftrace.