[PATCH] x86_64: reliable stack trace support

These are the generic bits needed to enable reliable stack traces based
on Dwarf2-like (.eh_frame) unwind information. Subsequent patches will
enable x86-64 and i386 to make use of this.

Thanks to Andi Kleen and Ingo Molnar, who pointed out several possibilities
for improvement.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/unwind.h

@@ -0,0 +1,119 @@
+#ifndef _LINUX_UNWIND_H
+#define _LINUX_UNWIND_H
+
+/*
+ * Copyright (C) 2002-2006 Novell, Inc.
+ *	Jan Beulich <jbeulich@novell.com>
+ * This code is released under version 2 of the GNU GPL.
+ *
+ * A simple API for unwinding kernel stacks.  This is used for
+ * debugging and error reporting purposes.  The kernel doesn't need
+ * full-blown stack unwinding with all the bells and whistles, so there
+ * is not much point in implementing the full Dwarf2 unwind API.
+ */
+
+#include <linux/config.h>
+
+struct module;
+
+#ifdef CONFIG_STACK_UNWIND
+
+#include <asm/unwind.h>
+
+#ifndef ARCH_UNWIND_SECTION_NAME
+#define ARCH_UNWIND_SECTION_NAME ".eh_frame"
+#endif
+
+/*
+ * Initialize unwind support.
+ */
+extern void unwind_init(void);
+
+extern void *unwind_add_table(struct module *,
+                              const void *table_start,
+                              unsigned long table_size);
+
+extern void unwind_remove_table(void *handle, int init_only);
+
+extern int unwind_init_frame_info(struct unwind_frame_info *,
+                                  struct task_struct *,
+                                  /*const*/ struct pt_regs *);
+
+/*
+ * Prepare to unwind a blocked task.
+ */
+extern int unwind_init_blocked(struct unwind_frame_info *,
+                               struct task_struct *);
+
+/*
+ * Prepare to unwind the currently running thread.
+ */
+extern int unwind_init_running(struct unwind_frame_info *,
+                               asmlinkage void (*callback)(struct unwind_frame_info *,
+                                                           void *arg),
+                               void *arg);
+
+/*
+ * Unwind to previous to frame.  Returns 0 if successful, negative
+ * number in case of an error.
+ */
+extern int unwind(struct unwind_frame_info *);
+
+/*
+ * Unwind until the return pointer is in user-land (or until an error
+ * occurs).  Returns 0 if successful, negative number in case of
+ * error.
+ */
+extern int unwind_to_user(struct unwind_frame_info *);
+
+#else
+
+struct unwind_frame_info {};
+
+static inline void unwind_init(void) {}
+
+static inline void *unwind_add_table(struct module *mod,
+                                     const void *table_start,
+                                     unsigned long table_size)
+{
+	return NULL;
+}
+
+static inline void unwind_remove_table(void *handle, int init_only)
+{
+}
+
+static inline int unwind_init_frame_info(struct unwind_frame_info *info,
+                                         struct task_struct *tsk,
+                                         const struct pt_regs *regs)
+{
+	return -ENOSYS;
+}
+
+static inline int unwind_init_blocked(struct unwind_frame_info *info,
+                                      struct task_struct *tsk)
+{
+	return -ENOSYS;
+}
+
+static inline int unwind_init_running(struct unwind_frame_info *info,
+                                      asmlinkage void (*cb)(struct unwind_frame_info *,
+                                                            void *arg),
+                                      void *arg)
+{
+	return -ENOSYS;
+}
+
+static inline int unwind(struct unwind_frame_info *info)
+{
+	return -ENOSYS;
+}
+
+static inline int unwind_to_user(struct unwind_frame_info *info)
+{
+	return -ENOSYS;
+}
+
+#endif
+
+#endif /* _LINUX_UNWIND_H */