Add kernel support for oprofile callgraphs on AVR32

This patch adds backtracing capability to oprofile profiling in kernel
and user mode on AVR32. This is done by going through the frames on the
stack and adding oprofile traces for all return addresses. The code
being profiled has to be compiled with frame pointers to make this work.

Signed-off-by: Nikolaus Voss <n.voss@weinmann.de>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>

arch/avr32/oprofile/Makefile

@@ -5,4 +5,4 @@ oprofile-y		:= $(addprefix ../../../drivers/oprofile/,	\
 				event_buffer.o oprofile_files.o		\
 				oprofilefs.o oprofile_stats.o		\
 				timer_int.o)
-oprofile-y		+= op_model_avr32.o
+oprofile-y		+= op_model_avr32.o backtrace.o

arch/avr32/oprofile/backtrace.c

@@ -0,0 +1,81 @@
+/*
+ * AVR32 specific backtracing code for oprofile
+ *
+ * Copyright 2008 Weinmann GmbH
+ *
+ * Author: Nikolaus Voss <n.voss@weinmann.de>
+ *
+ * Based on i386 oprofile backtrace code by John Levon and David Smith
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/oprofile.h>
+#include <linux/sched.h>
+#include <linux/uaccess.h>
+
+/* The first two words of each frame on the stack look like this if we have
+ * frame pointers */
+struct frame_head {
+	unsigned long lr;
+	struct frame_head *fp;
+};
+
+/* copied from arch/avr32/kernel/process.c */
+static inline int valid_stack_ptr(struct thread_info *tinfo, unsigned long p)
+{
+	return (p > (unsigned long)tinfo)
+		&& (p < (unsigned long)tinfo + THREAD_SIZE - 3);
+}
+
+/* copied from arch/x86/oprofile/backtrace.c */
+static struct frame_head *dump_user_backtrace(struct frame_head *head)
+{
+	struct frame_head bufhead[2];
+
+	/* Also check accessibility of one struct frame_head beyond */
+	if (!access_ok(VERIFY_READ, head, sizeof(bufhead)))
+		return NULL;
+	if (__copy_from_user_inatomic(bufhead, head, sizeof(bufhead)))
+		return NULL;
+
+	oprofile_add_trace(bufhead[0].lr);
+
+	/* frame pointers should strictly progress back up the stack
+	 * (towards higher addresses) */
+	if (bufhead[0].fp <= head)
+		return NULL;
+
+	return bufhead[0].fp;
+}
+
+void avr32_backtrace(struct pt_regs * const regs, unsigned int depth)
+{
+	/* Get first frame pointer */
+	struct frame_head *head = (struct frame_head *)(regs->r7);
+
+	if (!user_mode(regs)) {
+#ifdef CONFIG_FRAME_POINTER
+		/*
+		 * Traverse the kernel stack from frame to frame up to
+		 * "depth" steps.
+		 */
+		while (depth-- && valid_stack_ptr(task_thread_info(current),
+						  (unsigned long)head)) {
+			oprofile_add_trace(head->lr);
+			if (head->fp <= head)
+				break;
+			head = head->fp;
+		}
+#endif
+	} else {
+		/* Assume we have frame pointers in user mode process */
+		while (depth-- && head)
+			head = dump_user_backtrace(head);
+	}
+}
+
+

arch/avr32/oprofile/op_model_avr32.c

@@ -22,6 +22,8 @@
 #define AVR32_PERFCTR_IRQ_GROUP	0
 #define AVR32_PERFCTR_IRQ_LINE	1
 
+void avr32_backtrace(struct pt_regs * const regs, unsigned int depth);
+
 enum { PCCNT, PCNT0, PCNT1, NR_counter };
 
 struct avr32_perf_counter {
@@ -223,6 +225,8 @@ int __init oprofile_arch_init(struct oprofile_operations *ops)
 	memcpy(ops, &avr32_perf_counter_ops,
 			sizeof(struct oprofile_operations));
 
+	ops->backtrace = avr32_backtrace;
+
 	printk(KERN_INFO "oprofile: using AVR32 performance monitoring.\n");
 
 	return 0;