sh: oprofile: Backtrace support.

This patch improves the oprofile support on sh and adds backtrace
support.
Signed-off-by: Dave Peverley <dpeverley@mpc-data.co.uk>
Signed-off-by: Chris Smith <chris.smith@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/oprofile/backtrace.c

+/*
+ * SH specific backtracing code for oprofile
+ *
+ * Copyright 2007 STMicroelectronics Ltd.
+ *
+ * Author: Dave Peverley <dpeverley@mpc-data.co.uk>
+ *
+ * Based on ARM oprofile backtrace code by Richard Purdie and in turn, i386
+ * oprofile backtrace code by John Levon, 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/kallsyms.h>
+#include <linux/mm.h>
+#include <asm/ptrace.h>
+#include <asm/uaccess.h>
+#include <asm/sections.h>
+
+/* Limit to stop backtracing too far. */
+static int backtrace_limit = 20;
+
+static unsigned long *
+user_backtrace(unsigned long *stackaddr, struct pt_regs *regs)
+{
+	unsigned long buf_stack;
+
+	/* Also check accessibility of address */
+	if (!access_ok(VERIFY_READ, stackaddr, sizeof(unsigned long)))
+		return NULL;
+
+	if (__copy_from_user_inatomic(&buf_stack, stackaddr, sizeof(unsigned long)))
+		return NULL;
+
+	/* Quick paranoia check */
+	if (buf_stack & 3)
+		return NULL;
+
+	oprofile_add_trace(buf_stack);
+
+	stackaddr++;
+
+	return stackaddr;
+}
+
+/*
+ * |             | /\ Higher addresses
+ * |             |
+ * --------------- stack base (address of current_thread_info)
+ * | thread info |
+ * .             .
+ * |    stack    |
+ * --------------- saved regs->regs[15] value if valid
+ * .             .
+ * --------------- struct pt_regs stored on stack (struct pt_regs *)
+ * |             |
+ * .             .
+ * |             |
+ * --------------- ???
+ * |             |
+ * |             | \/ Lower addresses
+ *
+ * Thus, &pt_regs <-> stack base restricts the valid(ish) fp values
+ */
+static int valid_kernel_stack(unsigned long *stackaddr, struct pt_regs *regs)
+{
+	unsigned long stack = (unsigned long)regs;
+	unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
+
+	return ((unsigned long)stackaddr > stack) && ((unsigned long)stackaddr < stack_base);
+}
+
+static unsigned long *
+kernel_backtrace(unsigned long *stackaddr, struct pt_regs *regs)
+{
+	unsigned long addr;
+
+	/*
+	 * If not a valid kernel address, keep going till we find one
+	 * or the SP stops being a valid address.
+	 */
+	do {
+		addr = *stackaddr++;
+
+		if (__kernel_text_address(addr)) {
+			oprofile_add_trace(addr);
+			break;
+		}
+	} while (valid_kernel_stack(stackaddr, regs));
+
+	return stackaddr;
+}
+
+void sh_backtrace(struct pt_regs * const regs, unsigned int depth)
+{
+	unsigned long *stackaddr;
+
+	/*
+	 * Paranoia - clip max depth as we could get lost in the weeds.
+	 */
+	if (depth > backtrace_limit)
+		depth = backtrace_limit;
+
+	stackaddr = (unsigned long *)regs->regs[15];
+	if (!user_mode(regs)) {
+		while (depth-- && valid_kernel_stack(stackaddr, regs))
+			stackaddr = kernel_backtrace(stackaddr, regs);
+
+		return;
+	}
+
+	while (depth-- && (stackaddr != NULL))
+		stackaddr = user_backtrace(stackaddr, regs);
+}

arch/sh/oprofile/common.c

@@ -27,6 +27,8 @@ static struct op_sh_model *model;
 
 static struct op_counter_config ctr[20];
 
+extern void sh_backtrace(struct pt_regs * const regs, unsigned int depth);
+
 static int op_sh_setup(void)
 {
 	/* Pre-compute the values to stuff in the hardware registers.  */
@@ -85,6 +87,13 @@ int __init oprofile_arch_init(struct oprofile_operations *ops)
 	struct op_sh_model *lmodel = NULL;
 	int ret;
 
+	/*
+	 * Always assign the backtrace op. If the counter initialization
+	 * fails, we fall back to the timer which will still make use of
+	 * this.
+	 */
+	ops->backtrace = sh_backtrace;
+
 	switch (current_cpu_data.type) {
 	/* SH-4 types */
 	case CPU_SH7750: