4 files changed, 190 insertions, 3 deletions

diff --git a/arch/sh/include/asm/unwinder.h b/arch/sh/include/asm/unwinder.h
new file mode 100644
index 00000000000..3dc551453e2
--- /dev/null
+++ b/arch/sh/include/asm/unwinder.h
@@ -0,0 +1,25 @@
+#ifndef _LINUX_UNWINDER_H
+#define _LINUX_UNWINDER_H
+
+#include <asm/stacktrace.h>
+
+struct unwinder {
+	const char *name;
+	struct list_head list;
+	int rating;
+	void (*dump)(struct task_struct *, struct pt_regs *,
+		     unsigned long *, const struct stacktrace_ops *, void *);
+};
+
+extern int unwinder_init(void);
+extern int unwinder_register(struct unwinder *);
+
+extern void unwind_stack(struct task_struct *, struct pt_regs *,
+			 unsigned long *, const struct stacktrace_ops *,
+			 void *);
+
+extern void stack_reader_dump(struct task_struct *, struct pt_regs *,
+			      unsigned long *, const struct stacktrace_ops *,
+			      void *);
+
+#endif /* _LINUX_UNWINDER_H */
diff --git a/arch/sh/kernel/Makefile_32 b/arch/sh/kernel/Makefile_32
index 6b32de701a7..37a3b7704fc 100644
--- a/arch/sh/kernel/Makefile_32
+++ b/arch/sh/kernel/Makefile_32
@@ -11,8 +11,8 @@ endif
 
 obj-y	:= debugtraps.o dumpstack.o idle.o io.o io_generic.o irq.o	\
 	   machvec.o process_32.o ptrace_32.o setup.o signal_32.o	\
-	   sys_sh.o sys_sh32.o syscalls_32.o time.o topology.o	\
-	   traps.o traps_32.o
+	   sys_sh.o sys_sh32.o syscalls_32.o time.o topology.o		\
+	   traps.o traps_32.o unwinder.o
 
 obj-y				+= cpu/
 obj-$(CONFIG_VSYSCALL)		+= vsyscall/
diff --git a/arch/sh/kernel/Makefile_64 b/arch/sh/kernel/Makefile_64
index 67b9f6c6326..00b73e7598c 100644
--- a/arch/sh/kernel/Makefile_64
+++ b/arch/sh/kernel/Makefile_64
@@ -2,7 +2,7 @@ extra-y	:= head_64.o init_task.o vmlinux.lds
 
 obj-y	:= debugtraps.o idle.o io.o io_generic.o irq.o machvec.o process_64.o \
 	   ptrace_64.o setup.o signal_64.o sys_sh.o sys_sh64.o \
-	   syscalls_64.o time.o topology.o traps.o traps_64.o
+	   syscalls_64.o time.o topology.o traps.o traps_64.o unwinder.o
 
 obj-y				+= cpu/
 obj-$(CONFIG_SMP)		+= smp.o
diff --git a/arch/sh/kernel/unwinder.c b/arch/sh/kernel/unwinder.c
new file mode 100644
index 00000000000..2b30fa28b44
--- /dev/null
+++ b/arch/sh/kernel/unwinder.c
@@ -0,0 +1,162 @@
+/*
+ * Copyright (C) 2009  Matt Fleming
+ *
+ * Based, in part, on kernel/time/clocksource.c.
+ *
+ * This file provides arbitration code for stack unwinders.
+ *
+ * Multiple stack unwinders can be available on a system, usually with
+ * the most accurate unwinder being the currently active one.
+ */
+#include <linux/errno.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <asm/unwinder.h>
+#include <asm/atomic.h>
+
+/*
+ * This is the most basic stack unwinder an architecture can
+ * provide. For architectures without reliable frame pointers, e.g.
+ * RISC CPUs, it can be implemented by looking through the stack for
+ * addresses that lie within the kernel text section.
+ *
+ * Other CPUs, e.g. x86, can use their frame pointer register to
+ * construct more accurate stack traces.
+ */
+static struct list_head unwinder_list;
+static struct unwinder stack_reader = {
+	.name = "stack-reader",
+	.dump = stack_reader_dump,
+	.rating = 50,
+	.list = {
+		.next = &unwinder_list,
+		.prev = &unwinder_list,
+	},
+};
+
+/*
+ * "curr_unwinder" points to the stack unwinder currently in use. This
+ * is the unwinder with the highest rating.
+ *
+ * "unwinder_list" is a linked-list of all available unwinders, sorted
+ * by rating.
+ *
+ * All modifications of "curr_unwinder" and "unwinder_list" must be
+ * performed whilst holding "unwinder_lock".
+ */
+static struct unwinder *curr_unwinder = &stack_reader;
+
+static struct list_head unwinder_list = {
+	.next = &stack_reader.list,
+	.prev = &stack_reader.list,
+};
+
+static DEFINE_SPINLOCK(unwinder_lock);
+
+static atomic_t unwinder_running = ATOMIC_INIT(0);
+
+/**
+ * select_unwinder - Select the best registered stack unwinder.
+ *
+ * Private function. Must hold unwinder_lock when called.
+ *
+ * Select the stack unwinder with the best rating. This is useful for
+ * setting up curr_unwinder.
+ */
+static struct unwinder *select_unwinder(void)
+{
+	struct unwinder *best;
+
+	if (list_empty(&unwinder_list))
+		return NULL;
+
+	best = list_entry(unwinder_list.next, struct unwinder, list);
+	if (best == curr_unwinder)
+		return NULL;
+
+	return best;
+}
+
+/*
+ * Enqueue the stack unwinder sorted by rating.
+ */
+static int unwinder_enqueue(struct unwinder *ops)
+{
+	struct list_head *tmp, *entry = &unwinder_list;
+
+	list_for_each(tmp, &unwinder_list) {
+		struct unwinder *o;
+
+		o = list_entry(tmp, struct unwinder, list);
+		if (o == ops)
+			return -EBUSY;
+		/* Keep track of the place, where to insert */
+		if (o->rating >= ops->rating)
+			entry = tmp;
+	}
+	list_add(&ops->list, entry);
+
+	return 0;
+}
+
+/**
+ * unwinder_register - Used to install new stack unwinder
+ * @u: unwinder to be registered
+ *
+ * Install the new stack unwinder on the unwinder list, which is sorted
+ * by rating.
+ *
+ * Returns -EBUSY if registration fails, zero otherwise.
+ */
+int unwinder_register(struct unwinder *u)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&unwinder_lock, flags);
+	ret = unwinder_enqueue(u);
+	if (!ret)
+		curr_unwinder = select_unwinder();
+	spin_unlock_irqrestore(&unwinder_lock, flags);
+
+	return ret;
+}
+
+/*
+ * Unwind the call stack and pass information to the stacktrace_ops
+ * functions. Also handle the case where we need to switch to a new
+ * stack dumper because the current one faulted unexpectedly.
+ */
+void unwind_stack(struct task_struct *task, struct pt_regs *regs,
+		  unsigned long *sp, const struct stacktrace_ops *ops,
+		  void *data)
+{
+	unsigned long flags;
+
+	/*
+	 * The problem with unwinders with high ratings is that they are
+	 * inherently more complicated than the simple ones with lower
+	 * ratings. We are therefore more likely to fault in the
+	 * complicated ones, e.g. hitting BUG()s. If we fault in the
+	 * code for the current stack unwinder we try to downgrade to
+	 * one with a lower rating.
+	 *
+	 * Hopefully this will give us a semi-reliable stacktrace so we
+	 * can diagnose why curr_unwinder->dump() faulted.
+	 */
+	if (atomic_inc_return(&unwinder_running) != 1) {
+		spin_lock_irqsave(&unwinder_lock, flags);
+
+		if (!list_is_singular(&unwinder_list)) {
+			list_del(&curr_unwinder->list);
+			curr_unwinder = select_unwinder();
+		}
+
+		spin_unlock_irqrestore(&unwinder_lock, flags);
+		atomic_dec(&unwinder_running);
+	}
+
+	curr_unwinder->dump(task, regs, sp, ops, data);
+
+	atomic_dec(&unwinder_running);
+}