[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>

3 files changed, 129 insertions, 0 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3c5e4c2e517d..5c1ec1f84eab 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -32,6 +32,7 @@ extern const char linux_banner[];
 
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
 #define ALIGN(x,a) (((x)+(a)-1)&~((a)-1))
+#define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
 
 #define	KERN_EMERG	"<0>"	/* system is unusable			*/
 #define	KERN_ALERT	"<1>"	/* action must be taken immediately	*/
@@ -336,6 +337,12 @@ struct sysinfo {
 /* Force a compilation error if condition is true */
 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
 
+/* Force a compilation error if condition is true, but also produce a
+   result (of value 0 and type size_t), so the expression can be used
+   e.g. in a structure initializer (or where-ever else comma expressions
+   aren't permitted). */
+#define BUILD_BUG_ON_ZERO(e) (sizeof(char[1 - 2 * !!(e)]) - 1)
+
 /* Trap pasters of __FUNCTION__ at compile-time */
 #define __FUNCTION__ (__func__)
 
diff --git a/include/linux/module.h b/include/linux/module.h
index 2d366098eab5..9ebbb74b7b72 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -285,6 +285,9 @@ struct module
 	/* The size of the executable code in each section.  */
 	unsigned long init_text_size, core_text_size;
 
+	/* The handle returned from unwind_add_table. */
+	void *unwind_info;
+
 	/* Arch-specific module values */
 	struct mod_arch_specific arch;
 
diff --git a/include/linux/unwind.h b/include/linux/unwind.h
new file mode 100644
index 000000000000..0295aa789ab4
--- /dev/null
+++ b/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 */