Subject: DWARF2 EH-frame based stack unwinding
From: jbeulich@novell.com
Patch-mainline: no

This includes reverting f1883f86dea84fe47a71a39fc1afccc005915ed8.

Update Jan 17 2009 jeffm:
- Something in 2.6.29-rc1 tweaked the frame pointer code somehow, so I fixed
  that up.

---
 Makefile                          |    5 
 arch/x86/Kconfig                  |    2 
 arch/x86/Makefile                 |    2 
 arch/x86/include/asm/system.h     |   10 
 arch/x86/include/asm/unwind.h     |  163 ++++
 arch/x86/kernel/dumpstack.c       |   89 ++
 arch/x86/kernel/dumpstack.h       |    4 
 arch/x86/kernel/dumpstack_32.c    |   18 
 arch/x86/kernel/dumpstack_64.c    |   20 
 arch/x86/kernel/entry_32.S        |   35 +
 arch/x86/kernel/entry_64.S        |   34 
 include/asm-generic/vmlinux.lds.h |   22 
 include/linux/module.h            |    3 
 include/linux/unwind.h            |  135 +++
 init/main.c                       |    3 
 kernel/Makefile                   |    1 
 kernel/module.c                   |   15 
 kernel/unwind.c                   | 1303 ++++++++++++++++++++++++++++++++++++++
 lib/Kconfig.debug                 |   18 
 19 files changed, 1866 insertions(+), 16 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -570,6 +570,11 @@ else
 KBUILD_CFLAGS	+= -fomit-frame-pointer
 endif
 
+ifdef CONFIG_UNWIND_INFO
+KBUILD_CFLAGS	+= -fasynchronous-unwind-tables
+LDFLAGS_vmlinux	+= --eh-frame-hdr
+endif
+
 ifdef CONFIG_DEBUG_INFO
 KBUILD_CFLAGS	+= -g
 KBUILD_AFLAGS	+= -gdwarf-2
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -487,7 +487,7 @@ config X86_ES7000
 config SCHED_OMIT_FRAME_POINTER
 	def_bool y
 	prompt "Single-depth WCHAN output"
-	depends on X86
+	depends on X86 && !STACK_UNWIND
 	---help---
 	  Calculate simpler /proc/<PID>/wchan values. If this option
 	  is disabled then wchan values will recurse back to the
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -105,7 +105,9 @@ KBUILD_CFLAGS += -pipe
 # Workaround for a gcc prelease that unfortunately was shipped in a suse release
 KBUILD_CFLAGS += -Wno-sign-compare
 #
+ifneq ($(CONFIG_UNWIND_INFO),y)
 KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
+endif
 # prevent gcc from generating any FP code by mistake
 KBUILD_CFLAGS += $(call cc-option,-mno-sse -mno-mmx -mno-sse2 -mno-3dnow,)
 
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -123,12 +123,22 @@ do {									\
 #define __switch_canary_iparam
 #endif	/* CC_STACKPROTECTOR */
 
+/* The stack unwind code needs this but it pollutes traces otherwise */
+#ifdef CONFIG_UNWIND_INFO
+#define THREAD_RETURN_SYM \
+	".globl thread_return\n" \
+	"thread_return:\n\t"
+#else
+#define THREAD_RETURN_SYM
+#endif
+
 /* Save restore flags to clear handle leaking NT */
 #define switch_to(prev, next, last) \
 	asm volatile(SAVE_CONTEXT					  \
 	     "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */	  \
 	     "movq %P[threadrsp](%[next]),%%rsp\n\t" /* restore RSP */	  \
 	     "call __switch_to\n\t"					  \
+	     THREAD_RETURN_SYM						  \
 	     "movq "__percpu_arg([current_task])",%%rsi\n\t"		  \
 	     __switch_canary						  \
 	     "movq %P[thread_info](%%rsi),%%r8\n\t"			  \
--- /dev/null
+++ b/arch/x86/include/asm/unwind.h
@@ -0,0 +1,163 @@
+#ifndef _ASM_X86_UNWIND_H
+#define _ASM_X86_UNWIND_H
+
+/*
+ * Copyright (C) 2002-2009 Novell, Inc.
+ *	Jan Beulich <jbeulich@novell.com>
+ * This code is released under version 2 of the GNU GPL.
+ */
+
+#ifdef CONFIG_STACK_UNWIND
+
+#include <linux/sched.h>
+#include <linux/uaccess.h>
+#include <asm/ptrace.h>
+
+struct unwind_frame_info
+{
+	struct pt_regs regs;
+	struct task_struct *task;
+	unsigned call_frame:1;
+};
+
+#define UNW_PC(frame)      (frame)->regs.ip
+#define UNW_SP(frame)      (frame)->regs.sp
+#ifdef CONFIG_FRAME_POINTER
+#define UNW_FP(frame)      (frame)->regs.bp
+#define FRAME_LINK_OFFSET  0
+#define STACK_BOTTOM(tsk)  STACK_LIMIT((tsk)->thread.sp0)
+#define TSK_STACK_TOP(tsk) ((tsk)->thread.sp0)
+#else
+#define UNW_FP(frame)      ((void)(frame), 0UL)
+#endif
+/* On x86-64, might need to account for the special exception and interrupt
+   handling stacks here, since normally
+	EXCEPTION_STACK_ORDER < THREAD_ORDER < IRQSTACK_ORDER,
+   but the construct is needed only for getting across the stack switch to
+   the interrupt stack - thus considering the IRQ stack itself is unnecessary,
+   and the overhead of comparing against all exception handling stacks seems
+   not desirable. */
+#define STACK_LIMIT(ptr)   (((ptr) - 1) & ~(THREAD_SIZE - 1))
+
+#ifdef CONFIG_X86_64
+
+#include <asm/vsyscall.h>
+
+#define FRAME_RETADDR_OFFSET 8
+
+#define UNW_REGISTER_INFO \
+	PTREGS_INFO(ax), \
+	PTREGS_INFO(dx), \
+	PTREGS_INFO(cx), \
+	PTREGS_INFO(bx), \
+	PTREGS_INFO(si), \
+	PTREGS_INFO(di), \
+	PTREGS_INFO(bp), \
+	PTREGS_INFO(sp), \
+	PTREGS_INFO(r8), \
+	PTREGS_INFO(r9), \
+	PTREGS_INFO(r10), \
+	PTREGS_INFO(r11), \
+	PTREGS_INFO(r12), \
+	PTREGS_INFO(r13), \
+	PTREGS_INFO(r14), \
+	PTREGS_INFO(r15), \
+	PTREGS_INFO(ip)
+
+#else /* X86_32 */
+
+#include <asm/fixmap.h>
+
+#define FRAME_RETADDR_OFFSET 4
+
+#define UNW_REGISTER_INFO \
+	PTREGS_INFO(ax), \
+	PTREGS_INFO(cx), \
+	PTREGS_INFO(dx), \
+	PTREGS_INFO(bx), \
+	PTREGS_INFO(sp), \
+	PTREGS_INFO(bp), \
+	PTREGS_INFO(si), \
+	PTREGS_INFO(di), \
+	PTREGS_INFO(ip)
+
+#endif
+
+#define UNW_DEFAULT_RA(raItem, dataAlign) \
+	((raItem).where == Memory && \
+	 !((raItem).value * (dataAlign) + sizeof(void *)))
+
+static inline void arch_unw_init_frame_info(struct unwind_frame_info *info,
+                                            /*const*/ struct pt_regs *regs)
+{
+#ifdef CONFIG_X86_64
+	info->regs = *regs;
+#else
+	if (user_mode_vm(regs))
+		info->regs = *regs;
+	else {
+		memcpy(&info->regs, regs, offsetof(struct pt_regs, sp));
+		info->regs.sp = (unsigned long)&regs->sp;
+		info->regs.ss = __KERNEL_DS;
+	}
+#endif
+}
+
+static inline void arch_unw_init_blocked(struct unwind_frame_info *info)
+{
+#ifdef CONFIG_X86_64
+	extern const char thread_return[];
+
+	memset(&info->regs, 0, sizeof(info->regs));
+	info->regs.ip = (unsigned long)thread_return;
+	info->regs.cs = __KERNEL_CS;
+	probe_kernel_address(info->task->thread.sp, info->regs.bp);
+	info->regs.sp = info->task->thread.sp;
+	info->regs.ss = __KERNEL_DS;
+#else
+	memset(&info->regs, 0, sizeof(info->regs));
+	info->regs.ip = info->task->thread.ip;
+	info->regs.cs = __KERNEL_CS;
+	probe_kernel_address(info->task->thread.sp, info->regs.bp);
+	info->regs.sp = info->task->thread.sp;
+	info->regs.ss = __KERNEL_DS;
+	info->regs.ds = __USER_DS;
+	info->regs.es = __USER_DS;
+#endif
+}
+
+extern asmlinkage int
+arch_unwind_init_running(struct unwind_frame_info *,
+			 unwind_callback_fn,
+			 const struct stacktrace_ops *, void *data);
+
+static inline int arch_unw_user_mode(/*const*/ struct unwind_frame_info *info)
+{
+#ifdef CONFIG_X86_64
+	return user_mode(&info->regs)
+	       || (long)info->regs.ip >= 0
+	       || (info->regs.ip >= VSYSCALL_START && info->regs.ip < VSYSCALL_END)
+	       || (long)info->regs.sp >= 0;
+#else
+	return user_mode_vm(&info->regs)
+	       || info->regs.ip < PAGE_OFFSET
+	       || (info->regs.ip >= __fix_to_virt(FIX_VDSO)
+	           && info->regs.ip < __fix_to_virt(FIX_VDSO) + PAGE_SIZE)
+	       || info->regs.sp < PAGE_OFFSET;
+#endif
+}
+
+#else
+
+#define UNW_PC(frame) ((void)(frame), 0UL)
+#define UNW_SP(frame) ((void)(frame), 0UL)
+#define UNW_FP(frame) ((void)(frame), 0UL)
+
+static inline int arch_unw_user_mode(const void *info)
+{
+	return 0;
+}
+
+#endif
+
+#endif /* _ASM_X86_UNWIND_H */
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -20,6 +20,7 @@
 #endif
 
 #include <asm/stacktrace.h>
+#include <linux/unwind.h>
 
 #include "dumpstack.h"
 
@@ -27,6 +28,11 @@ int panic_on_unrecovered_nmi;
 int panic_on_io_nmi;
 unsigned int code_bytes = 64;
 int kstack_depth_to_print = 3 * STACKSLOTS_PER_LINE;
+#ifdef CONFIG_STACK_UNWIND
+static int call_trace = 1;
+#else
+#define call_trace (-1)
+#endif
 static int die_counter;
 
 void printk_address(unsigned long address, int reliable)
@@ -66,6 +72,71 @@ print_ftrace_graph_addr(unsigned long ad
 { }
 #endif
 
+int asmlinkage dump_trace_unwind(struct unwind_frame_info *info,
+		      const struct stacktrace_ops *ops, void *data)
+{
+	int n = 0;
+#ifdef CONFIG_UNWIND_INFO
+	unsigned long sp = UNW_SP(info);
+
+	if (arch_unw_user_mode(info))
+		return -1;
+	while (unwind(info) == 0 && UNW_PC(info)) {
+		n++;
+		ops->address(data, UNW_PC(info), 1);
+		if (arch_unw_user_mode(info))
+			break;
+		if ((sp & ~(PAGE_SIZE - 1)) == (UNW_SP(info) & ~(PAGE_SIZE - 1))
+		    && sp > UNW_SP(info))
+			break;
+		sp = UNW_SP(info);
+	}
+#endif
+	return n;
+}
+
+int try_stack_unwind(struct task_struct *task, struct pt_regs *regs,
+		     unsigned long **stack, unsigned long *bp,
+		     const struct stacktrace_ops *ops, void *data)
+{
+#ifdef CONFIG_UNWIND_INFO
+	int unw_ret = 0;
+	struct unwind_frame_info info;
+	if (call_trace < 0)
+		return 0;
+
+	if (regs) {
+		if (unwind_init_frame_info(&info, task, regs) == 0)
+			unw_ret = dump_trace_unwind(&info, ops, data);
+	} else if (task == current)
+		unw_ret = unwind_init_running(&info, dump_trace_unwind, ops, data);
+	else {
+		if (unwind_init_blocked(&info, task) == 0)
+			unw_ret = dump_trace_unwind(&info, ops, data);
+	}
+	if (unw_ret > 0) {
+		if (call_trace == 1 && !arch_unw_user_mode(&info)) {
+			ops->warning_symbol(data, "DWARF2 unwinder stuck at %s\n",
+				     UNW_PC(&info));
+			if ((long)UNW_SP(&info) < 0) {
+				ops->warning(data, "Leftover inexact backtrace:\n");
+				*stack = (unsigned long *)UNW_SP(&info);
+				if (!stack) {
+					*bp = UNW_FP(&info);
+					return -1;
+				}
+			} else
+				ops->warning(data, "Full inexact backtrace again:\n");
+		} else if (call_trace >= 1) {
+			return -1;
+		} else
+			ops->warning(data, "Full inexact backtrace again:\n");
+	} else
+		ops->warning(data, "Inexact backtrace:\n");
+#endif
+	return 0;
+}
+
 /*
  * x86-64 can have up to three kernel stacks:
  * process stack
@@ -396,3 +467,21 @@ static int __init code_bytes_setup(char
 	return 1;
 }
 __setup("code_bytes=", code_bytes_setup);
+
+#ifdef CONFIG_STACK_UNWIND
+static int __init call_trace_setup(char *s)
+{
+	if (!s)
+		return -EINVAL;
+	if (strcmp(s, "old") == 0)
+		call_trace = -1;
+	else if (strcmp(s, "both") == 0)
+		call_trace = 0;
+	else if (strcmp(s, "newfallback") == 0)
+		call_trace = 1;
+	else if (strcmp(s, "new") == 0)
+		call_trace = 2;
+	return 0;
+}
+early_param("call_trace", call_trace_setup);
+#endif
--- a/arch/x86/kernel/dumpstack.h
+++ b/arch/x86/kernel/dumpstack.h
@@ -22,6 +22,10 @@ extern void
 show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 		unsigned long *sp, unsigned long bp, char *log_lvl);
 
+int try_stack_unwind(struct task_struct *task, struct pt_regs *regs,
+                     unsigned long **stack, unsigned long *bp,
+                     const struct stacktrace_ops *ops, void *data);
+
 extern unsigned int code_bytes;
 
 /* The form of the top of the frame on the stack */
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -28,14 +28,6 @@ void dump_trace(struct task_struct *task
 	if (!task)
 		task = current;
 
-	if (!stack) {
-		unsigned long dummy;
-
-		stack = &dummy;
-		if (task && task != current)
-			stack = (unsigned long *)task->thread.sp;
-	}
-
 #ifdef CONFIG_FRAME_POINTER
 	if (!bp) {
 		if (task == current) {
@@ -48,6 +40,16 @@ void dump_trace(struct task_struct *task
 	}
 #endif
 
+	if (try_stack_unwind(task, regs, &stack, &bp, ops, data))
+		return;
+
+	if (!stack) {
+		unsigned long dummy;
+		stack = &dummy;
+		if (task && task != current)
+			stack = (unsigned long *)task->thread.sp;
+	}
+
 	for (;;) {
 		struct thread_info *context;
 
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -14,6 +14,7 @@
 #include <linux/bug.h>
 #include <linux/nmi.h>
 
+#include <linux/unwind.h>
 #include <asm/stacktrace.h>
 
 #include "dumpstack.h"
@@ -154,13 +155,6 @@ void dump_trace(struct task_struct *task
 	if (!task)
 		task = current;
 
-	if (!stack) {
-		unsigned long dummy;
-		stack = &dummy;
-		if (task && task != current)
-			stack = (unsigned long *)task->thread.sp;
-	}
-
 #ifdef CONFIG_FRAME_POINTER
 	if (!bp) {
 		if (task == current) {
@@ -173,6 +167,18 @@ void dump_trace(struct task_struct *task
 	}
 #endif
 
+	if (try_stack_unwind(task, regs, &stack, &bp, ops, data)) {
+		put_cpu();
+		return;
+	}
+
+	if (!stack) {
+		unsigned long dummy;
+		stack = &dummy;
+		if (task && task != current)
+			stack = (unsigned long *)task->thread.sp;
+	}
+
 	/*
 	 * Print function call entries in all stacks, starting at the
 	 * current stack address. If the stacks consist of nested
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1064,6 +1064,41 @@ END(spurious_interrupt_bug)
  */
 	.popsection
 
+#ifdef CONFIG_STACK_UNWIND
+ENTRY(arch_unwind_init_running)
+	CFI_STARTPROC
+	movl	4(%esp), %edx
+	movl	(%esp), %ecx
+	leal	4(%esp), %eax
+	movl	%ebx, PT_EBX(%edx)
+	xorl	%ebx, %ebx
+	movl	%ebx, PT_ECX(%edx)
+	movl	%ebx, PT_EDX(%edx)
+	movl	%esi, PT_ESI(%edx)
+	movl	%edi, PT_EDI(%edx)
+	movl	%ebp, PT_EBP(%edx)
+	movl	%ebx, PT_EAX(%edx)
+	movl	$__USER_DS, PT_DS(%edx)
+	movl	$__USER_DS, PT_ES(%edx)
+	movl	$__KERNEL_PERCPU, PT_FS(%edx)
+	movl	$__KERNEL_STACK_CANARY, PT_GS(%edx)
+	movl	%eax, PT_OLDESP(%edx)
+	movl	16(%esp), %eax
+	movl	%ebx, PT_ORIG_EAX(%edx)
+	movl	%ecx, PT_EIP(%edx)
+	movl	12(%esp), %ecx
+	movl	$__KERNEL_CS, PT_CS(%edx)
+	movl	%eax, 12(%esp)
+	movl	8(%esp), %eax
+	movl	%ecx, 8(%esp)
+	movl	%ebx, PT_EFLAGS(%edx)
+	movl	PT_EBX(%edx), %ebx
+	movl	$__KERNEL_DS, PT_OLDSS(%edx)
+	jmpl	*%eax
+	CFI_ENDPROC
+ENDPROC(arch_unwind_init_running)
+#endif
+
 ENTRY(kernel_thread_helper)
 	pushl $0		# fake return address for unwinder
 	CFI_STARTPROC
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1232,6 +1232,40 @@ ENTRY(call_softirq)
 	CFI_ENDPROC
 END(call_softirq)
 
+#ifdef CONFIG_STACK_UNWIND
+ENTRY(arch_unwind_init_running)
+	CFI_STARTPROC
+	movq	%r15, R15(%rdi)
+	movq	%r14, R14(%rdi)
+	xchgq	%rsi, %rdx
+	movq	%r13, R13(%rdi)
+	movq	%r12, R12(%rdi)
+	xorl	%eax, %eax
+	movq	%rbp, RBP(%rdi)
+	movq	%rbx, RBX(%rdi)
+	movq	(%rsp), %r9
+	xchgq	%rdx, %rcx
+	movq	%rax, R11(%rdi)
+	movq	%rax, R10(%rdi)
+	movq	%rax, R9(%rdi)
+	movq	%rax, R8(%rdi)
+	movq	%rax, RAX(%rdi)
+	movq	%rax, RCX(%rdi)
+	movq	%rax, RDX(%rdi)
+	movq	%rax, RSI(%rdi)
+	movq	%rax, RDI(%rdi)
+	movq	%rax, ORIG_RAX(%rdi)
+	movq	%r9, RIP(%rdi)
+	leaq	8(%rsp), %r9
+	movq	$__KERNEL_CS, CS(%rdi)
+	movq	%rax, EFLAGS(%rdi)
+	movq	%r9, RSP(%rdi)
+	movq	$__KERNEL_DS, SS(%rdi)
+	jmpq	*%rcx
+	CFI_ENDPROC
+END(arch_unwind_init_running)
+#endif
+
 #ifdef CONFIG_XEN
 zeroentry xen_hypervisor_callback xen_do_hypervisor_callback
 
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -341,6 +341,8 @@
 		MEM_KEEP(exit.rodata)					\
 	}								\
 									\
+	EH_FRAME							\
+									\
 	/* Built-in module parameters. */				\
 	__param : AT(ADDR(__param) - LOAD_OFFSET) {			\
 		VMLINUX_SYMBOL(__start___param) = .;			\
@@ -758,3 +760,23 @@
 	BSS(bss_align)							\
 	. = ALIGN(stop_align);						\
 	VMLINUX_SYMBOL(__bss_stop) = .;
+
+#ifdef CONFIG_STACK_UNWIND
+#define EH_FRAME							\
+		/* Unwind data binary search table */			\
+		. = ALIGN(8);						\
+		.eh_frame_hdr : AT(ADDR(.eh_frame_hdr) - LOAD_OFFSET) {	\
+			VMLINUX_SYMBOL(__start_unwind_hdr) = .;		\
+			*(.eh_frame_hdr)				\
+			VMLINUX_SYMBOL(__end_unwind_hdr) = .;		\
+		}							\
+		/* Unwind data */					\
+		. = ALIGN(8);						\
+		.eh_frame : AT(ADDR(.eh_frame) - LOAD_OFFSET) {		\
+			VMLINUX_SYMBOL(__start_unwind) = .;		\
+			*(.eh_frame)					\
+			VMLINUX_SYMBOL(__end_unwind) = .;		\
+		}
+#else
+#define EH_FRAME
+#endif
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -301,6 +301,9 @@ struct module
 	/* The size of the executable code in each section.  */
 	unsigned int 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;
 
--- /dev/null
+++ b/include/linux/unwind.h
@@ -0,0 +1,135 @@
+#ifndef _LINUX_UNWIND_H
+#define _LINUX_UNWIND_H
+
+/*
+ * Copyright (C) 2002-2009 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/linkage.h>
+
+struct module;
+struct stacktrace_ops;
+struct unwind_frame_info;
+
+typedef asmlinkage int (*unwind_callback_fn)(struct unwind_frame_info *,
+					     const struct stacktrace_ops *,
+					     void *);
+
+#ifdef CONFIG_STACK_UNWIND
+
+#include <asm/unwind.h>
+#include <asm/stacktrace.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_setup(void);
+
+#ifdef CONFIG_MODULES
+
+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);
+
+#endif
+
+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 *,
+			       unwind_callback_fn,
+			       const struct stacktrace_ops *,
+                               void *data);
+
+/*
+ * 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 /* CONFIG_STACK_UNWIND */
+
+struct unwind_frame_info {};
+
+static inline void unwind_init(void) {}
+static inline void unwind_setup(void) {}
+
+#ifdef CONFIG_MODULES
+
+static inline void *unwind_add_table(struct module *mod,
+                                     const void *table_start,
+                                     unsigned long table_size)
+{
+	return NULL;
+}
+
+#endif
+
+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,
+			       unwind_callback_fn cb,
+			       const struct stacktrace_ops *ops,
+                                      void *data)
+{
+	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 /* CONFIG_STACK_UNWIND */
+#endif /* _LINUX_UNWIND_H */
--- a/init/main.c
+++ b/init/main.c
@@ -50,6 +50,7 @@
 #include <linux/rmap.h>
 #include <linux/mempolicy.h>
 #include <linux/key.h>
+#include <linux/unwind.h>
 #include <linux/buffer_head.h>
 #include <linux/page_cgroup.h>
 #include <linux/debug_locks.h>
@@ -560,6 +561,7 @@ asmlinkage void __init start_kernel(void
 	 * Need to run as early as possible, to initialize the
 	 * lockdep hash:
 	 */
+	unwind_init();
 	lockdep_init();
 	debug_objects_early_init();
 
@@ -586,6 +588,7 @@ asmlinkage void __init start_kernel(void
 	setup_arch(&command_line);
 	mm_init_owner(&init_mm, &init_task);
 	setup_command_line(command_line);
+	unwind_setup();
 	setup_nr_cpu_ids();
 	setup_per_cpu_areas();
 	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -53,6 +53,7 @@ obj-$(CONFIG_PROVE_LOCKING) += spinlock.
 obj-$(CONFIG_UID16) += uid16.o
 obj-$(CONFIG_MODULES) += module.o
 obj-$(CONFIG_KALLSYMS) += kallsyms.o
+obj-$(CONFIG_STACK_UNWIND) += unwind.o
 obj-$(CONFIG_PM) += power/
 obj-$(CONFIG_FREEZER) += power/
 obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -44,6 +44,7 @@
 #include <linux/device.h>
 #include <linux/string.h>
 #include <linux/mutex.h>
+#include <linux/unwind.h>
 #include <linux/rculist.h>
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -1501,6 +1502,8 @@ static void free_module(struct module *m
 	remove_sect_attrs(mod);
 	mod_kobject_remove(mod);
 
+	unwind_remove_table(mod->unwind_info, 0);
+
 	/* Arch-specific cleanup. */
 	module_arch_cleanup(mod);
 
@@ -2064,6 +2067,7 @@ static noinline struct module *load_modu
 	unsigned int symindex = 0;
 	unsigned int strindex = 0;
 	unsigned int modindex, versindex, infoindex, pcpuindex;
+	unsigned int unwindex = 0;
 	struct module *mod;
 	long err = 0;
 	void *ptr = NULL; /* Stops spurious gcc warning */
@@ -2146,10 +2150,15 @@ static noinline struct module *load_modu
 	versindex = find_sec(hdr, sechdrs, secstrings, "__versions");
 	infoindex = find_sec(hdr, sechdrs, secstrings, ".modinfo");
 	pcpuindex = find_pcpusec(hdr, sechdrs, secstrings);
+#ifdef ARCH_UNWIND_SECTION_NAME
+	unwindex = find_sec(hdr, sechdrs, secstrings, ARCH_UNWIND_SECTION_NAME);
+#endif
 
 	/* Don't keep modinfo and version sections. */
 	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
 	sechdrs[versindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
+	if (unwindex)
+		sechdrs[unwindex].sh_flags |= SHF_ALLOC;
 
 	/* Check module struct version now, before we try to use module. */
 	if (!check_modstruct_version(sechdrs, versindex, mod)) {
@@ -2511,6 +2520,11 @@ static noinline struct module *load_modu
 	}
 #endif
 
+	/* Size of section 0 is 0, so this works well if no unwind info. */
+	mod->unwind_info = unwind_add_table(mod,
+					    (void *)sechdrs[unwindex].sh_addr,
+					    sechdrs[unwindex].sh_size);
+
 	/* Get rid of temporary copy */
 	vfree(hdr);
 
@@ -2632,6 +2646,7 @@ SYSCALL_DEFINE3(init_module, void __user
 	/* Drop initial reference. */
 	module_put(mod);
 	trim_init_extable(mod);
+	unwind_remove_table(mod->unwind_info, 1);
 #ifdef CONFIG_KALLSYMS
 	mod->num_symtab = mod->core_num_syms;
 	mod->symtab = mod->core_symtab;
--- /dev/null
+++ b/kernel/unwind.c
@@ -0,0 +1,1303 @@
+/*
+ * 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/unwind.h>
+#include <linux/module.h>
+#include <linux/bootmem.h>
+#include <linux/sort.h>
+#include <linux/stop_machine.h>
+#include <linux/uaccess.h>
+#include <asm/sections.h>
+#include <asm/unaligned.h>
+#include <linux/slab.h>
+
+extern const char __start_unwind[], __end_unwind[];
+extern const u8 __start_unwind_hdr[], __end_unwind_hdr[];
+
+#define MAX_STACK_DEPTH 8
+
+#define EXTRA_INFO(f) { \
+		BUILD_BUG_ON_ZERO(offsetof(struct unwind_frame_info, f) \
+		                  % FIELD_SIZEOF(struct unwind_frame_info, f)) \
+		+ offsetof(struct unwind_frame_info, f) \
+		  / FIELD_SIZEOF(struct unwind_frame_info, f), \
+		FIELD_SIZEOF(struct unwind_frame_info, f) \
+	}
+#define PTREGS_INFO(f) EXTRA_INFO(regs.f)
+
+static const struct {
+	unsigned offs:BITS_PER_LONG / 2;
+	unsigned width:BITS_PER_LONG / 2;
+} reg_info[] = {
+	UNW_REGISTER_INFO
+};
+
+#undef PTREGS_INFO
+#undef EXTRA_INFO
+
+#ifndef REG_INVALID
+#define REG_INVALID(r) (reg_info[r].width == 0)
+#endif
+
+#define DW_CFA_nop                          0x00
+#define DW_CFA_set_loc                      0x01
+#define DW_CFA_advance_loc1                 0x02
+#define DW_CFA_advance_loc2                 0x03
+#define DW_CFA_advance_loc4                 0x04
+#define DW_CFA_offset_extended              0x05
+#define DW_CFA_restore_extended             0x06
+#define DW_CFA_undefined                    0x07
+#define DW_CFA_same_value                   0x08
+#define DW_CFA_register                     0x09
+#define DW_CFA_remember_state               0x0a
+#define DW_CFA_restore_state                0x0b
+#define DW_CFA_def_cfa                      0x0c
+#define DW_CFA_def_cfa_register             0x0d
+#define DW_CFA_def_cfa_offset               0x0e
+#define DW_CFA_def_cfa_expression           0x0f
+#define DW_CFA_expression                   0x10
+#define DW_CFA_offset_extended_sf           0x11
+#define DW_CFA_def_cfa_sf                   0x12
+#define DW_CFA_def_cfa_offset_sf            0x13
+#define DW_CFA_val_offset                   0x14
+#define DW_CFA_val_offset_sf                0x15
+#define DW_CFA_val_expression               0x16
+#define DW_CFA_lo_user                      0x1c
+#define DW_CFA_GNU_window_save              0x2d
+#define DW_CFA_GNU_args_size                0x2e
+#define DW_CFA_GNU_negative_offset_extended 0x2f
+#define DW_CFA_hi_user                      0x3f
+
+#define DW_EH_PE_FORM     0x07
+#define DW_EH_PE_native   0x00
+#define DW_EH_PE_leb128   0x01
+#define DW_EH_PE_data2    0x02
+#define DW_EH_PE_data4    0x03
+#define DW_EH_PE_data8    0x04
+#define DW_EH_PE_signed   0x08
+#define DW_EH_PE_ADJUST   0x70
+#define DW_EH_PE_abs      0x00
+#define DW_EH_PE_pcrel    0x10
+#define DW_EH_PE_textrel  0x20
+#define DW_EH_PE_datarel  0x30
+#define DW_EH_PE_funcrel  0x40
+#define DW_EH_PE_aligned  0x50
+#define DW_EH_PE_indirect 0x80
+#define DW_EH_PE_omit     0xff
+
+typedef unsigned long uleb128_t;
+typedef   signed long sleb128_t;
+#define sleb128abs __builtin_labs
+
+static struct unwind_table {
+	struct {
+		unsigned long pc;
+		unsigned long range;
+	} core, init;
+	const void *address;
+	unsigned long size;
+	const unsigned char *header;
+	unsigned long hdrsz;
+	struct unwind_table *link;
+	const char *name;
+} root_table;
+
+struct unwind_item {
+	enum item_location {
+		Nowhere,
+		Memory,
+		Register,
+		Value
+	} where;
+	uleb128_t value;
+};
+
+struct unwind_state {
+	uleb128_t loc, org;
+	const u8 *cieStart, *cieEnd;
+	uleb128_t codeAlign;
+	sleb128_t dataAlign;
+	struct cfa {
+		uleb128_t reg, offs;
+	} cfa;
+	struct unwind_item regs[ARRAY_SIZE(reg_info)];
+	unsigned stackDepth:8;
+	unsigned version:8;
+	const u8 *label;
+	const u8 *stack[MAX_STACK_DEPTH];
+};
+
+static const struct cfa badCFA = { ARRAY_SIZE(reg_info), 1 };
+
+static unsigned unwind_debug;
+static int __init unwind_debug_setup(char *s)
+{
+	unwind_debug = simple_strtoul(s, NULL, 0);
+	return 1;
+}
+__setup("unwind_debug=", unwind_debug_setup);
+#define dprintk(lvl, fmt, args...) \
+	((void)(lvl > unwind_debug \
+	 || printk(KERN_DEBUG "unwind: " fmt "\n", ##args)))
+
+static struct unwind_table *find_table(unsigned long pc)
+{
+	struct unwind_table *table;
+
+	for (table = &root_table; table; table = table->link)
+		if ((pc >= table->core.pc
+		     && pc < table->core.pc + table->core.range)
+		    || (pc >= table->init.pc
+		        && pc < table->init.pc + table->init.range))
+			break;
+
+	return table;
+}
+
+static unsigned long read_pointer(const u8 **pLoc,
+                                  const void *end,
+                                  signed ptrType,
+                                  unsigned long text_base,
+                                  unsigned long data_base);
+
+static void init_unwind_table(struct unwind_table *table,
+                              const char *name,
+                              const void *core_start,
+                              unsigned long core_size,
+                              const void *init_start,
+                              unsigned long init_size,
+                              const void *table_start,
+                              unsigned long table_size,
+                              const u8 *header_start,
+                              unsigned long header_size)
+{
+	const u8 *ptr = header_start + 4;
+	const u8 *end = header_start + header_size;
+
+	table->core.pc = (unsigned long)core_start;
+	table->core.range = core_size;
+	table->init.pc = (unsigned long)init_start;
+	table->init.range = init_size;
+	table->address = table_start;
+	table->size = table_size;
+	/* See if the linker provided table looks valid. */
+	if (header_size <= 4
+	    || header_start[0] != 1
+	    || (void *)read_pointer(&ptr, end, header_start[1], 0, 0)
+	       != table_start
+	    || !read_pointer(&ptr, end, header_start[2], 0, 0)
+	    || !read_pointer(&ptr, end, header_start[3], 0,
+	                     (unsigned long)header_start)
+	    || !read_pointer(&ptr, end, header_start[3], 0,
+	                     (unsigned long)header_start))
+		header_start = NULL;
+	table->hdrsz = header_size;
+	smp_wmb();
+	table->header = header_start;
+	table->link = NULL;
+	table->name = name;
+}
+
+void __init unwind_init(void)
+{
+	init_unwind_table(&root_table, "kernel",
+	                  _text, _end - _text,
+	                  NULL, 0,
+	                  __start_unwind, __end_unwind - __start_unwind,
+	                  __start_unwind_hdr, __end_unwind_hdr - __start_unwind_hdr);
+}
+
+static const u32 bad_cie, not_fde;
+static const u32 *cie_for_fde(const u32 *fde, const struct unwind_table *);
+static signed fde_pointer_type(const u32 *cie);
+
+struct eh_frame_hdr_table_entry {
+	unsigned long start, fde;
+};
+
+static int cmp_eh_frame_hdr_table_entries(const void *p1, const void *p2)
+{
+	const struct eh_frame_hdr_table_entry *e1 = p1;
+	const struct eh_frame_hdr_table_entry *e2 = p2;
+
+	return (e1->start > e2->start) - (e1->start < e2->start);
+}
+
+static void swap_eh_frame_hdr_table_entries(void *p1, void *p2, int size)
+{
+	struct eh_frame_hdr_table_entry *e1 = p1;
+	struct eh_frame_hdr_table_entry *e2 = p2;
+	unsigned long v;
+
+	v = e1->start;
+	e1->start = e2->start;
+	e2->start = v;
+	v = e1->fde;
+	e1->fde = e2->fde;
+	e2->fde = v;
+}
+
+static void __init setup_unwind_table(struct unwind_table *table,
+					void *(*alloc)(unsigned long))
+{
+	const u8 *ptr;
+	unsigned long tableSize = table->size, hdrSize;
+	unsigned n;
+	const u32 *fde;
+	struct {
+		u8 version;
+		u8 eh_frame_ptr_enc;
+		u8 fde_count_enc;
+		u8 table_enc;
+		unsigned long eh_frame_ptr;
+		unsigned int fde_count;
+		struct eh_frame_hdr_table_entry table[];
+	} __attribute__((__packed__)) *header;
+
+	if (table->header)
+		return;
+
+	if (table->hdrsz)
+		printk(KERN_WARNING ".eh_frame_hdr for '%s' present but unusable\n",
+		       table->name);
+
+	if (tableSize & (sizeof(*fde) - 1))
+		return;
+
+	for (fde = table->address, n = 0;
+	     tableSize > sizeof(*fde) && tableSize - sizeof(*fde) >= *fde;
+	     tableSize -= sizeof(*fde) + *fde, fde += 1 + *fde / sizeof(*fde)) {
+		const u32 *cie = cie_for_fde(fde, table);
+		signed ptrType;
+
+		if (cie == &not_fde)
+			continue;
+		if (cie == NULL
+		    || cie == &bad_cie
+		    || (ptrType = fde_pointer_type(cie)) < 0)
+			return;
+		ptr = (const u8 *)(fde + 2);
+		if (!read_pointer(&ptr,
+		                  (const u8 *)(fde + 1) + *fde,
+		                  ptrType, 0, 0))
+			return;
+		++n;
+	}
+
+	if (tableSize || !n)
+		return;
+
+	hdrSize = 4 + sizeof(unsigned long) + sizeof(unsigned int)
+	        + 2 * n * sizeof(unsigned long);
+	dprintk(2, "Binary lookup table size for %s: %lu bytes", table->name, hdrSize);
+	header = alloc(hdrSize);
+	if (!header)
+		return;
+	header->version          = 1;
+	header->eh_frame_ptr_enc = DW_EH_PE_abs|DW_EH_PE_native;
+	header->fde_count_enc    = DW_EH_PE_abs|DW_EH_PE_data4;
+	header->table_enc        = DW_EH_PE_abs|DW_EH_PE_native;
+	put_unaligned((unsigned long)table->address, &header->eh_frame_ptr);
+	BUILD_BUG_ON(offsetof(typeof(*header), fde_count)
+	             % __alignof(typeof(header->fde_count)));
+	header->fde_count        = n;
+
+	BUILD_BUG_ON(offsetof(typeof(*header), table)
+	             % __alignof(typeof(*header->table)));
+	for (fde = table->address, tableSize = table->size, n = 0;
+	     tableSize;
+	     tableSize -= sizeof(*fde) + *fde, fde += 1 + *fde / sizeof(*fde)) {
+		const u32 *cie = fde + 1 - fde[1] / sizeof(*fde);
+
+		if (!fde[1])
+			continue; /* this is a CIE */
+		ptr = (const u8 *)(fde + 2);
+		header->table[n].start = read_pointer(&ptr,
+		                                      (const u8 *)(fde + 1) + *fde,
+		                                      fde_pointer_type(cie), 0, 0);
+		header->table[n].fde = (unsigned long)fde;
+		++n;
+	}
+	WARN_ON(n != header->fde_count);
+
+	sort(header->table,
+	     n,
+	     sizeof(*header->table),
+	     cmp_eh_frame_hdr_table_entries,
+	     swap_eh_frame_hdr_table_entries);
+
+	table->hdrsz = hdrSize;
+	smp_wmb();
+	table->header = (const void *)header;
+}
+
+static void *__init balloc(unsigned long sz)
+{
+	return __alloc_bootmem_nopanic(sz,
+	                               sizeof(unsigned int),
+	                               __pa(MAX_DMA_ADDRESS));
+}
+
+void __init unwind_setup(void)
+{
+	setup_unwind_table(&root_table, balloc);
+}
+
+#ifdef CONFIG_MODULES
+
+static struct unwind_table *last_table;
+
+/* Must be called with module_mutex held. */
+void *unwind_add_table(struct module *module,
+                       const void *table_start,
+                       unsigned long table_size)
+{
+	struct unwind_table *table;
+
+	if (table_size <= 0)
+		return NULL;
+
+	table = kmalloc(sizeof(*table), GFP_KERNEL);
+	if (!table)
+		return NULL;
+
+	init_unwind_table(table, module->name,
+	                  module->module_core, module->core_size,
+	                  module->module_init, module->init_size,
+	                  table_start, table_size,
+	                  NULL, 0);
+
+	if (last_table)
+		last_table->link = table;
+	else
+		root_table.link = table;
+	last_table = table;
+
+	return table;
+}
+
+struct unlink_table_info
+{
+	struct unwind_table *table;
+	int init_only;
+};
+
+static int unlink_table(void *arg)
+{
+	struct unlink_table_info *info = arg;
+	struct unwind_table *table = info->table, *prev;
+
+	for (prev = &root_table; prev->link && prev->link != table; prev = prev->link)
+		;
+
+	if (prev->link) {
+		if (info->init_only) {
+			table->init.pc = 0;
+			table->init.range = 0;
+			info->table = NULL;
+		} else {
+			prev->link = table->link;
+			if (!prev->link)
+				last_table = prev;
+		}
+	} else
+		info->table = NULL;
+
+	return 0;
+}
+
+/* Must be called with module_mutex held. */
+void unwind_remove_table(void *handle, int init_only)
+{
+	struct unwind_table *table = handle;
+	struct unlink_table_info info;
+
+	if (!table || table == &root_table)
+		return;
+
+	if (init_only && table == last_table) {
+		table->init.pc = 0;
+		table->init.range = 0;
+		return;
+	}
+
+	info.table = table;
+	info.init_only = init_only;
+	stop_machine(unlink_table, &info, NULL);
+
+	if (info.table)
+		kfree(table);
+}
+
+#endif /* CONFIG_MODULES */
+
+static uleb128_t get_uleb128(const u8 **pcur, const u8 *end)
+{
+	const u8 *cur = *pcur;
+	uleb128_t value;
+	unsigned shift;
+
+	for (shift = 0, value = 0; cur < end; shift += 7) {
+		if (shift + 7 > 8 * sizeof(value)
+		    && (*cur & 0x7fU) >= (1U << (8 * sizeof(value) - shift))) {
+			cur = end + 1;
+			break;
+		}
+		value |= (uleb128_t)(*cur & 0x7f) << shift;
+		if (!(*cur++ & 0x80))
+			break;
+	}
+	*pcur = cur;
+
+	return value;
+}
+
+static sleb128_t get_sleb128(const u8 **pcur, const u8 *end)
+{
+	const u8 *cur = *pcur;
+	sleb128_t value;
+	unsigned shift;
+
+	for (shift = 0, value = 0; cur < end; shift += 7) {
+		if (shift + 7 > 8 * sizeof(value)
+		    && (*cur & 0x7fU) >= (1U << (8 * sizeof(value) - shift))) {
+			cur = end + 1;
+			break;
+		}
+		value |= (sleb128_t)(*cur & 0x7f) << shift;
+		if (!(*cur & 0x80)) {
+			value |= -(*cur++ & 0x40) << shift;
+			break;
+		}
+	}
+	*pcur = cur;
+
+	return value;
+}
+
+static const u32 *cie_for_fde(const u32 *fde, const struct unwind_table *table)
+{
+	const u32 *cie;
+
+	if (!*fde || (*fde & (sizeof(*fde) - 1)))
+		return &bad_cie;
+	if (!fde[1])
+		return &not_fde; /* this is a CIE */
+	if ((fde[1] & (sizeof(*fde) - 1))
+	    || fde[1] > (unsigned long)(fde + 1) - (unsigned long)table->address)
+		return NULL; /* this is not a valid FDE */
+	cie = fde + 1 - fde[1] / sizeof(*fde);
+	if (*cie <= sizeof(*cie) + 4
+	    || *cie >= fde[1] - sizeof(*fde)
+	    || (*cie & (sizeof(*cie) - 1))
+	    || cie[1])
+		return NULL; /* this is not a (valid) CIE */
+	return cie;
+}
+
+static unsigned long read_pointer(const u8 **pLoc,
+                                  const void *end,
+                                  signed ptrType,
+                                  unsigned long text_base,
+                                  unsigned long data_base)
+{
+	unsigned long value = 0;
+	union {
+		const u8 *p8;
+		const u16 *p16u;
+		const s16 *p16s;
+		const u32 *p32u;
+		const s32 *p32s;
+		const unsigned long *pul;
+	} ptr;
+
+	if (ptrType < 0 || ptrType == DW_EH_PE_omit) {
+		dprintk(1, "Invalid pointer encoding %02X (%p,%p).", ptrType, *pLoc, end);
+		return 0;
+	}
+	ptr.p8 = *pLoc;
+	switch (ptrType & DW_EH_PE_FORM) {
+	case DW_EH_PE_data2:
+		if (end < (const void *)(ptr.p16u + 1)) {
+			dprintk(1, "Data16 overrun (%p,%p).", ptr.p8, end);
+			return 0;
+		}
+		if (ptrType & DW_EH_PE_signed)
+			value = get_unaligned(ptr.p16s++);
+		else
+			value = get_unaligned(ptr.p16u++);
+		break;
+	case DW_EH_PE_data4:
+#ifdef CONFIG_64BIT
+		if (end < (const void *)(ptr.p32u + 1)) {
+			dprintk(1, "Data32 overrun (%p,%p).", ptr.p8, end);
+			return 0;
+		}
+		if (ptrType & DW_EH_PE_signed)
+			value = get_unaligned(ptr.p32s++);
+		else
+			value = get_unaligned(ptr.p32u++);
+		break;
+	case DW_EH_PE_data8:
+		BUILD_BUG_ON(sizeof(u64) != sizeof(value));
+#else
+		BUILD_BUG_ON(sizeof(u32) != sizeof(value));
+#endif
+	case DW_EH_PE_native:
+		if (end < (const void *)(ptr.pul + 1)) {
+			dprintk(1, "DataUL overrun (%p,%p).", ptr.p8, end);
+			return 0;
+		}
+		value = get_unaligned(ptr.pul++);
+		break;
+	case DW_EH_PE_leb128:
+		BUILD_BUG_ON(sizeof(uleb128_t) > sizeof(value));
+		value = ptrType & DW_EH_PE_signed
+		        ? get_sleb128(&ptr.p8, end)
+		        : get_uleb128(&ptr.p8, end);
+		if ((const void *)ptr.p8 > end) {
+			dprintk(1, "DataLEB overrun (%p,%p).", ptr.p8, end);
+			return 0;
+		}
+		break;
+	default:
+		dprintk(2, "Cannot decode pointer type %02X (%p,%p).",
+		        ptrType, ptr.p8, end);
+		return 0;
+	}
+	switch (ptrType & DW_EH_PE_ADJUST) {
+	case DW_EH_PE_abs:
+		break;
+	case DW_EH_PE_pcrel:
+		value += (unsigned long)*pLoc;
+		break;
+	case DW_EH_PE_textrel:
+		if (likely(text_base)) {
+			value += text_base;
+			break;
+		}
+		dprintk(2, "Text-relative encoding %02X (%p,%p), but zero text base.",
+		        ptrType, *pLoc, end);
+		return 0;
+	case DW_EH_PE_datarel:
+		if (likely(data_base)) {
+			value += data_base;
+			break;
+		}
+		dprintk(2, "Data-relative encoding %02X (%p,%p), but zero data base.",
+		        ptrType, *pLoc, end);
+		return 0;
+	default:
+		dprintk(2, "Cannot adjust pointer type %02X (%p,%p).",
+		        ptrType, *pLoc, end);
+		return 0;
+	}
+	if ((ptrType & DW_EH_PE_indirect)
+	    && probe_kernel_address(value, value)) {
+		dprintk(1, "Cannot read indirect value %lx (%p,%p).",
+		        value, *pLoc, end);
+		return 0;
+	}
+	*pLoc = ptr.p8;
+
+	return value;
+}
+
+static signed fde_pointer_type(const u32 *cie)
+{
+	const u8 *ptr = (const u8 *)(cie + 2);
+	unsigned version = *ptr;
+
+	if (version != 1)
+		return -1; /* unsupported */
+	if (*++ptr) {
+		const char *aug;
+		const u8 *end = (const u8 *)(cie + 1) + *cie;
+		uleb128_t len;
+
+		/* check if augmentation size is first (and thus present) */
+		if (*ptr != 'z')
+			return -1;
+		/* check if augmentation string is nul-terminated */
+		if ((ptr = memchr(aug = (const void *)ptr, 0, end - ptr)) == NULL)
+			return -1;
+		++ptr; /* skip terminator */
+		get_uleb128(&ptr, end); /* skip code alignment */
+		get_sleb128(&ptr, end); /* skip data alignment */
+		/* skip return address column */
+		version <= 1 ? (void)++ptr : (void)get_uleb128(&ptr, end);
+		len = get_uleb128(&ptr, end); /* augmentation length */
+		if (ptr + len < ptr || ptr + len > end)
+			return -1;
+		end = ptr + len;
+		while (*++aug) {
+			if (ptr >= end)
+				return -1;
+			switch (*aug) {
+			case 'L':
+				++ptr;
+				break;
+			case 'P': {
+					signed ptrType = *ptr++;
+
+					if (!read_pointer(&ptr, end, ptrType, 0, 0)
+					    || ptr > end)
+						return -1;
+				}
+				break;
+			case 'R':
+				return *ptr;
+			default:
+				return -1;
+			}
+		}
+	}
+	return DW_EH_PE_native|DW_EH_PE_abs;
+}
+
+static int advance_loc(unsigned long delta, struct unwind_state *state)
+{
+	state->loc += delta * state->codeAlign;
+
+	return delta > 0;
+}
+
+static void set_rule(uleb128_t reg,
+                     enum item_location where,
+                     uleb128_t value,
+                     struct unwind_state *state)
+{
+	if (reg < ARRAY_SIZE(state->regs)) {
+		state->regs[reg].where = where;
+		state->regs[reg].value = value;
+	}
+}
+
+static int processCFI(const u8 *start,
+                      const u8 *end,
+                      unsigned long targetLoc,
+                      signed ptrType,
+                      struct unwind_state *state)
+{
+	union {
+		const u8 *p8;
+		const u16 *p16;
+		const u32 *p32;
+	} ptr;
+	int result = 1;
+
+	if (start != state->cieStart) {
+		state->loc = state->org;
+		result = processCFI(state->cieStart, state->cieEnd, 0, ptrType, state);
+		if (targetLoc == 0 && state->label == NULL)
+			return result;
+	}
+	for (ptr.p8 = start; result && ptr.p8 < end; ) {
+		switch (*ptr.p8 >> 6) {
+			uleb128_t value;
+
+		case 0:
+			switch (*ptr.p8++) {
+			case DW_CFA_nop:
+				break;
+			case DW_CFA_set_loc:
+				state->loc = read_pointer(&ptr.p8, end, ptrType, 0, 0);
+				if (state->loc == 0)
+					result = 0;
+				break;
+			case DW_CFA_advance_loc1:
+				result = ptr.p8 < end && advance_loc(*ptr.p8++, state);
+				break;
+			case DW_CFA_advance_loc2:
+				result = ptr.p8 <= end + 2
+				         && advance_loc(*ptr.p16++, state);
+				break;
+			case DW_CFA_advance_loc4:
+				result = ptr.p8 <= end + 4
+				         && advance_loc(*ptr.p32++, state);
+				break;
+			case DW_CFA_offset_extended:
+				value = get_uleb128(&ptr.p8, end);
+				set_rule(value, Memory, get_uleb128(&ptr.p8, end), state);
+				break;
+			case DW_CFA_val_offset:
+				value = get_uleb128(&ptr.p8, end);
+				set_rule(value, Value, get_uleb128(&ptr.p8, end), state);
+				break;
+			case DW_CFA_offset_extended_sf:
+				value = get_uleb128(&ptr.p8, end);
+				set_rule(value, Memory, get_sleb128(&ptr.p8, end), state);
+				break;
+			case DW_CFA_val_offset_sf:
+				value = get_uleb128(&ptr.p8, end);
+				set_rule(value, Value, get_sleb128(&ptr.p8, end), state);
+				break;
+			case DW_CFA_restore_extended:
+			case DW_CFA_undefined:
+			case DW_CFA_same_value:
+				set_rule(get_uleb128(&ptr.p8, end), Nowhere, 0, state);
+				break;
+			case DW_CFA_register:
+				value = get_uleb128(&ptr.p8, end);
+				set_rule(value,
+				         Register,
+				         get_uleb128(&ptr.p8, end), state);
+				break;
+			case DW_CFA_remember_state:
+				if (ptr.p8 == state->label) {
+					state->label = NULL;
+					return 1;
+				}
+				if (state->stackDepth >= MAX_STACK_DEPTH) {
+					dprintk(1, "State stack overflow (%p,%p).", ptr.p8, end);
+					return 0;
+				}
+				state->stack[state->stackDepth++] = ptr.p8;
+				break;
+			case DW_CFA_restore_state:
+				if (state->stackDepth) {
+					const uleb128_t loc = state->loc;
+					const u8 *label = state->label;
+
+					state->label = state->stack[state->stackDepth - 1];
+					memcpy(&state->cfa, &badCFA, sizeof(state->cfa));
+					memset(state->regs, 0, sizeof(state->regs));
+					state->stackDepth = 0;
+					result = processCFI(start, end, 0, ptrType, state);
+					state->loc = loc;
+					state->label = label;
+				} else {
+					dprintk(1, "State stack underflow (%p,%p).", ptr.p8, end);
+					return 0;
+				}
+				break;
+			case DW_CFA_def_cfa:
+				state->cfa.reg = get_uleb128(&ptr.p8, end);
+				/*nobreak*/
+			case DW_CFA_def_cfa_offset:
+				state->cfa.offs = get_uleb128(&ptr.p8, end);
+				break;
+			case DW_CFA_def_cfa_sf:
+				state->cfa.reg = get_uleb128(&ptr.p8, end);
+				/*nobreak*/
+			case DW_CFA_def_cfa_offset_sf:
+				state->cfa.offs = get_sleb128(&ptr.p8, end)
+				                  * state->dataAlign;
+				break;
+			case DW_CFA_def_cfa_register:
+				state->cfa.reg = get_uleb128(&ptr.p8, end);
+				break;
+			/*todo case DW_CFA_def_cfa_expression: */
+			/*todo case DW_CFA_expression: */
+			/*todo case DW_CFA_val_expression: */
+			case DW_CFA_GNU_args_size:
+				get_uleb128(&ptr.p8, end);
+				break;
+			case DW_CFA_GNU_negative_offset_extended:
+				value = get_uleb128(&ptr.p8, end);
+				set_rule(value,
+				         Memory,
+				         (uleb128_t)0 - get_uleb128(&ptr.p8, end), state);
+				break;
+			case DW_CFA_GNU_window_save:
+			default:
+				dprintk(1, "Unrecognized CFI op %02X (%p,%p).", ptr.p8[-1], ptr.p8 - 1, end);
+				result = 0;
+				break;
+			}
+			break;
+		case 1:
+			result = advance_loc(*ptr.p8++ & 0x3f, state);
+			break;
+		case 2:
+			value = *ptr.p8++ & 0x3f;
+			set_rule(value, Memory, get_uleb128(&ptr.p8, end), state);
+			break;
+		case 3:
+			set_rule(*ptr.p8++ & 0x3f, Nowhere, 0, state);
+			break;
+		}
+		if (ptr.p8 > end) {
+			dprintk(1, "Data overrun (%p,%p).", ptr.p8, end);
+			result = 0;
+		}
+		if (result && targetLoc != 0 && targetLoc < state->loc)
+			return 1;
+	}
+
+	if (result && ptr.p8 < end)
+		dprintk(1, "Data underrun (%p,%p).", ptr.p8, end);
+
+	return result
+	       && ptr.p8 == end
+	       && (targetLoc == 0
+	           || (/*todo While in theory this should apply, gcc in practice omits
+	                 everything past the function prolog, and hence the location
+	                 never reaches the end of the function.
+	               targetLoc < state->loc &&*/ state->label == NULL));
+}
+
+/* Unwind to previous to frame.  Returns 0 if successful, negative
+ * number in case of an error. */
+int unwind(struct unwind_frame_info *frame)
+{
+#define FRAME_REG(r, t) (((t *)frame)[reg_info[r].offs])
+	const u32 *fde = NULL, *cie = NULL;
+	const u8 *ptr = NULL, *end = NULL;
+	unsigned long pc = UNW_PC(frame) - frame->call_frame, sp;
+	unsigned long startLoc = 0, endLoc = 0, cfa;
+	unsigned i;
+	signed ptrType = -1;
+	uleb128_t retAddrReg = 0;
+	const struct unwind_table *table;
+	struct unwind_state state;
+
+	if (UNW_PC(frame) == 0)
+		return -EINVAL;
+	if ((table = find_table(pc)) != NULL
+	    && !(table->size & (sizeof(*fde) - 1))) {
+		const u8 *hdr = table->header;
+		unsigned long tableSize;
+
+		smp_rmb();
+		if (hdr && hdr[0] == 1) {
+			switch (hdr[3] & DW_EH_PE_FORM) {
+			case DW_EH_PE_native: tableSize = sizeof(unsigned long); break;
+			case DW_EH_PE_data2: tableSize = 2; break;
+			case DW_EH_PE_data4: tableSize = 4; break;
+			case DW_EH_PE_data8: tableSize = 8; break;
+			default: tableSize = 0; break;
+			}
+			ptr = hdr + 4;
+			end = hdr + table->hdrsz;
+			if (tableSize
+			    && read_pointer(&ptr, end, hdr[1], 0, 0)
+			       == (unsigned long)table->address
+			    && (i = read_pointer(&ptr, end, hdr[2], 0, 0)) > 0
+			    && i == (end - ptr) / (2 * tableSize)
+			    && !((end - ptr) % (2 * tableSize))) {
+				do {
+					const u8 *cur = ptr + (i / 2) * (2 * tableSize);
+
+					startLoc = read_pointer(&cur,
+					                        cur + tableSize,
+					                        hdr[3], 0,
+					                        (unsigned long)hdr);
+					if (pc < startLoc)
+						i /= 2;
+					else {
+						ptr = cur - tableSize;
+						i = (i + 1) / 2;
+					}
+				} while (startLoc && i > 1);
+				if (i == 1
+				    && (startLoc = read_pointer(&ptr,
+				                                ptr + tableSize,
+				                                hdr[3], 0,
+				                                (unsigned long)hdr)) != 0
+				    && pc >= startLoc)
+					fde = (void *)read_pointer(&ptr,
+					                           ptr + tableSize,
+					                           hdr[3], 0,
+					                           (unsigned long)hdr);
+			}
+		}
+		if (hdr && !fde)
+			dprintk(3, "Binary lookup for %lx failed.", pc);
+
+		if (fde != NULL) {
+			cie = cie_for_fde(fde, table);
+			ptr = (const u8 *)(fde + 2);
+			if (cie != NULL
+			    && cie != &bad_cie
+			    && cie != &not_fde
+			    && (ptrType = fde_pointer_type(cie)) >= 0
+			    && read_pointer(&ptr,
+			                    (const u8 *)(fde + 1) + *fde,
+			                    ptrType, 0, 0) == startLoc) {
+				if (!(ptrType & DW_EH_PE_indirect))
+					ptrType &= DW_EH_PE_FORM|DW_EH_PE_signed;
+				endLoc = startLoc
+				         + read_pointer(&ptr,
+				                        (const u8 *)(fde + 1) + *fde,
+				                        ptrType, 0, 0);
+				if (pc >= endLoc)
+					fde = NULL;
+			} else
+				fde = NULL;
+			if (!fde)
+				dprintk(1, "Binary lookup result for %lx discarded.", pc);
+		}
+		if (fde == NULL) {
+			for (fde = table->address, tableSize = table->size;
+			     cie = NULL, tableSize > sizeof(*fde)
+			     && tableSize - sizeof(*fde) >= *fde;
+			     tableSize -= sizeof(*fde) + *fde,
+			     fde += 1 + *fde / sizeof(*fde)) {
+				cie = cie_for_fde(fde, table);
+				if (cie == &bad_cie) {
+					cie = NULL;
+					break;
+				}
+				if (cie == NULL
+				    || cie == &not_fde
+				    || (ptrType = fde_pointer_type(cie)) < 0)
+					continue;
+				ptr = (const u8 *)(fde + 2);
+				startLoc = read_pointer(&ptr,
+				                        (const u8 *)(fde + 1) + *fde,
+				                        ptrType, 0, 0);
+				if (!startLoc)
+					continue;
+				if (!(ptrType & DW_EH_PE_indirect))
+					ptrType &= DW_EH_PE_FORM|DW_EH_PE_signed;
+				endLoc = startLoc
+				         + read_pointer(&ptr,
+				                        (const u8 *)(fde + 1) + *fde,
+				                        ptrType, 0, 0);
+				if (pc >= startLoc && pc < endLoc)
+					break;
+			}
+			if (!fde)
+				dprintk(3, "Linear lookup for %lx failed.", pc);
+		}
+	}
+	if (cie != NULL) {
+		memset(&state, 0, sizeof(state));
+		state.cieEnd = ptr; /* keep here temporarily */
+		ptr = (const u8 *)(cie + 2);
+		end = (const u8 *)(cie + 1) + *cie;
+		frame->call_frame = 1;
+		if ((state.version = *ptr) != 1)
+			cie = NULL; /* unsupported version */
+		else if (*++ptr) {
+			/* check if augmentation size is first (and thus present) */
+			if (*ptr == 'z') {
+				while (++ptr < end && *ptr) {
+					switch (*ptr) {
+					/* check for ignorable (or already handled)
+					 * nul-terminated augmentation string */
+					case 'L':
+					case 'P':
+					case 'R':
+						continue;
+					case 'S':
+						frame->call_frame = 0;
+						continue;
+					default:
+						break;
+					}
+					break;
+				}
+			}
+			if (ptr >= end || *ptr)
+				cie = NULL;
+		}
+		if (!cie)
+			dprintk(1, "CIE unusable (%p,%p).", ptr, end);
+		++ptr;
+	}
+	if (cie != NULL) {
+		/* get code aligment factor */
+		state.codeAlign = get_uleb128(&ptr, end);
+		/* get data aligment factor */
+		state.dataAlign = get_sleb128(&ptr, end);
+		if (state.codeAlign == 0 || state.dataAlign == 0 || ptr >= end)
+			cie = NULL;
+		else if (UNW_PC(frame) % state.codeAlign
+		         || UNW_SP(frame) % sleb128abs(state.dataAlign)) {
+			dprintk(1, "Input pointer(s) misaligned (%lx,%lx).",
+			        UNW_PC(frame), UNW_SP(frame));
+			return -EPERM;
+		} else {
+			retAddrReg = state.version <= 1 ? *ptr++ : get_uleb128(&ptr, end);
+			/* skip augmentation */
+			if (((const char *)(cie + 2))[1] == 'z') {
+				uleb128_t augSize = get_uleb128(&ptr, end);
+
+				ptr += augSize;
+			}
+			if (ptr > end
+			    || retAddrReg >= ARRAY_SIZE(reg_info)
+			    || REG_INVALID(retAddrReg)
+			    || reg_info[retAddrReg].width != sizeof(unsigned long))
+				cie = NULL;
+		}
+		if (!cie)
+			dprintk(1, "CIE validation failed (%p,%p).", ptr, end);
+	}
+	if (cie != NULL) {
+		state.cieStart = ptr;
+		ptr = state.cieEnd;
+		state.cieEnd = end;
+		end = (const u8 *)(fde + 1) + *fde;
+		/* skip augmentation */
+		if (((const char *)(cie + 2))[1] == 'z') {
+			uleb128_t augSize = get_uleb128(&ptr, end);
+
+			if ((ptr += augSize) > end)
+				fde = NULL;
+		}
+		if (!fde)
+			dprintk(1, "FDE validation failed (%p,%p).", ptr, end);
+	}
+#ifdef CONFIG_FRAME_POINTER
+	if (cie == NULL || fde == NULL) {
+		unsigned long top = TSK_STACK_TOP(frame->task);
+		unsigned long bottom = STACK_BOTTOM(frame->task);
+		unsigned long fp = UNW_FP(frame);
+		unsigned long sp = UNW_SP(frame);
+		unsigned long link;
+
+		if ((sp | fp) & sizeof(unsigned long))
+			return -EPERM;
+
+# if FRAME_RETADDR_OFFSET < 0
+		if (!(sp < top && fp <= sp && bottom < fp))
+# else
+		if (!(sp < top && fp >= sp && bottom < fp))
+# endif
+			return -ENXIO;
+
+		if (probe_kernel_address(fp + FRAME_LINK_OFFSET, link))
+			return -ENXIO;
+
+# if FRAME_RETADDR_OFFSET < 0
+		if (!(link > bottom && link < fp))
+# else
+		if (!(link > bottom && link > fp))
+# endif
+			return -ENXIO;
+
+		if (link & (sizeof(unsigned long) - 1))
+			return -ENXIO;
+
+		fp += FRAME_RETADDR_OFFSET;
+		if (probe_kernel_address(fp, UNW_PC(frame)))
+			return -ENXIO;
+
+		/* Ok, we can use it */
+# if FRAME_RETADDR_OFFSET < 0
+		UNW_SP(frame) = fp - sizeof(UNW_PC(frame));
+# else
+		UNW_SP(frame) = fp + sizeof(UNW_PC(frame));
+# endif
+		UNW_FP(frame) = link;
+		return 0;
+	}
+#endif
+	state.org = startLoc;
+	memcpy(&state.cfa, &badCFA, sizeof(state.cfa));
+	/* process instructions */
+	if (!processCFI(ptr, end, pc, ptrType, &state)
+	    || state.loc > endLoc
+	    || state.regs[retAddrReg].where == Nowhere
+	    || state.cfa.reg >= ARRAY_SIZE(reg_info)
+	    || reg_info[state.cfa.reg].width != sizeof(unsigned long)
+	    || FRAME_REG(state.cfa.reg, unsigned long) % sizeof(unsigned long)
+	    || state.cfa.offs % sizeof(unsigned long)) {
+		dprintk(1, "Unusable unwind info (%p,%p).", ptr, end);
+		return -EIO;
+	}
+	/* update frame */
+#ifndef CONFIG_AS_CFI_SIGNAL_FRAME
+	if (frame->call_frame
+	    && !UNW_DEFAULT_RA(state.regs[retAddrReg], state.dataAlign))
+		frame->call_frame = 0;
+#endif
+	cfa = FRAME_REG(state.cfa.reg, unsigned long) + state.cfa.offs;
+	startLoc = min((unsigned long)UNW_SP(frame), cfa);
+	endLoc = max((unsigned long)UNW_SP(frame), cfa);
+	if (STACK_LIMIT(startLoc) != STACK_LIMIT(endLoc)) {
+		startLoc = min(STACK_LIMIT(cfa), cfa);
+		endLoc = max(STACK_LIMIT(cfa), cfa);
+	}
+#ifndef CONFIG_64BIT
+# define CASES CASE(8); CASE(16); CASE(32)
+#else
+# define CASES CASE(8); CASE(16); CASE(32); CASE(64)
+#endif
+	pc = UNW_PC(frame);
+	sp = UNW_SP(frame);
+	for (i = 0; i < ARRAY_SIZE(state.regs); ++i) {
+		if (REG_INVALID(i)) {
+			if (state.regs[i].where == Nowhere)
+				continue;
+			dprintk(1, "Cannot restore register %u (%d).",
+			        i, state.regs[i].where);
+			return -EIO;
+		}
+		switch (state.regs[i].where) {
+		default:
+			break;
+		case Register:
+			if (state.regs[i].value >= ARRAY_SIZE(reg_info)
+			    || REG_INVALID(state.regs[i].value)
+			    || reg_info[i].width > reg_info[state.regs[i].value].width) {
+				dprintk(1, "Cannot restore register %u from register %lu.",
+				        i, state.regs[i].value);
+				return -EIO;
+			}
+			switch (reg_info[state.regs[i].value].width) {
+#define CASE(n) \
+			case sizeof(u##n): \
+				state.regs[i].value = FRAME_REG(state.regs[i].value, \
+				                                const u##n); \
+				break
+			CASES;
+#undef CASE
+			default:
+				dprintk(1, "Unsupported register size %u (%lu).",
+				        reg_info[state.regs[i].value].width,
+				        state.regs[i].value);
+				return -EIO;
+			}
+			break;
+		}
+	}
+	for (i = 0; i < ARRAY_SIZE(state.regs); ++i) {
+		if (REG_INVALID(i))
+			continue;
+		switch (state.regs[i].where) {
+		case Nowhere:
+			if (reg_info[i].width != sizeof(UNW_SP(frame))
+			    || &FRAME_REG(i, __typeof__(UNW_SP(frame)))
+			       != &UNW_SP(frame))
+				continue;
+			UNW_SP(frame) = cfa;
+			break;
+		case Register:
+			switch (reg_info[i].width) {
+#define CASE(n) case sizeof(u##n): \
+				FRAME_REG(i, u##n) = state.regs[i].value; \
+				break
+			CASES;
+#undef CASE
+			default:
+				dprintk(1, "Unsupported register size %u (%u).",
+				        reg_info[i].width, i);
+				return -EIO;
+			}
+			break;
+		case Value:
+			if (reg_info[i].width != sizeof(unsigned long)) {
+				dprintk(1, "Unsupported value size %u (%u).",
+				        reg_info[i].width, i);
+				return -EIO;
+			}
+			FRAME_REG(i, unsigned long) = cfa + state.regs[i].value
+			                                    * state.dataAlign;
+			break;
+		case Memory: {
+				unsigned long addr = cfa + state.regs[i].value
+				                           * state.dataAlign;
+
+				if ((state.regs[i].value * state.dataAlign)
+				    % sizeof(unsigned long)
+				    || addr < startLoc
+				    || addr + sizeof(unsigned long) < addr
+				    || addr + sizeof(unsigned long) > endLoc) {
+					dprintk(1, "Bad memory location %lx (%lx).",
+					        addr, state.regs[i].value);
+					return -EIO;
+				}
+				switch (reg_info[i].width) {
+#define CASE(n)			case sizeof(u##n): \
+					if (probe_kernel_address(addr, \
+								 FRAME_REG(i, u##n))) \
+						return -EFAULT; \
+					break
+				CASES;
+#undef CASE
+				default:
+					dprintk(1, "Unsupported memory size %u (%u).",
+					        reg_info[i].width, i);
+					return -EIO;
+				}
+			}
+			break;
+		}
+	}
+
+	if (UNW_PC(frame) % state.codeAlign
+	    || UNW_SP(frame) % sleb128abs(state.dataAlign)) {
+		dprintk(1, "Output pointer(s) misaligned (%lx,%lx).",
+		        UNW_PC(frame), UNW_SP(frame));
+		return -EIO;
+	}
+	if (pc == UNW_PC(frame) && sp == UNW_SP(frame)) {
+		dprintk(1, "No progress (%lx,%lx).", pc, sp);
+		return -EIO;
+	}
+
+	return 0;
+#undef CASES
+#undef FRAME_REG
+}
+EXPORT_SYMBOL_GPL(unwind);
+
+int unwind_init_frame_info(struct unwind_frame_info *info,
+                           struct task_struct *tsk,
+                           /*const*/ struct pt_regs *regs)
+{
+	info->task = tsk;
+	info->call_frame = 0;
+	arch_unw_init_frame_info(info, regs);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(unwind_init_frame_info);
+
+/*
+ * Prepare to unwind a blocked task.
+ */
+int unwind_init_blocked(struct unwind_frame_info *info,
+                        struct task_struct *tsk)
+{
+	info->task = tsk;
+	info->call_frame = 0;
+	arch_unw_init_blocked(info);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(unwind_init_blocked);
+
+/*
+ * Prepare to unwind the currently running thread.
+ */
+int unwind_init_running(struct unwind_frame_info *info,
+			asmlinkage unwind_callback_fn callback,
+			const struct stacktrace_ops *ops, void *data)
+{
+	info->task = current;
+	info->call_frame = 0;
+
+	return arch_unwind_init_running(info, callback, ops, data);
+}
+EXPORT_SYMBOL_GPL(unwind_init_running);
+
+/*
+ * Unwind until the return pointer is in user-land (or until an error
+ * occurs).  Returns 0 if successful, negative number in case of
+ * error.
+ */
+int unwind_to_user(struct unwind_frame_info *info)
+{
+	while (!arch_unw_user_mode(info)) {
+		int err = unwind(info);
+
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(unwind_to_user);
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -742,6 +742,24 @@ config FRAME_POINTER
 	  larger and slower, but it gives very useful debugging information
 	  in case of kernel bugs. (precise oopses/stacktraces/warnings)
 
+config UNWIND_INFO
+	bool "Compile the kernel with frame unwind information"
+	depends on !IA64 && !PARISC && !ARM
+	depends on !MODULES || !(MIPS || PPC || SUPERH || V850)
+	help
+	  If you say Y here the resulting kernel image will be slightly larger
+	  but not slower, and it will give very useful debugging information.
+	  If you don't debug the kernel, you can say N, but we may not be able
+	  to solve problems without frame unwind information or frame pointers.
+
+config STACK_UNWIND
+	bool "Stack unwind support"
+	depends on UNWIND_INFO
+	depends on X86
+	help
+	  This enables more precise stack traces, omitting all unrelated
+	  occurrences of pointers into kernel code from the dump.
+
 config BOOT_PRINTK_DELAY
 	bool "Delay each boot printk message by N milliseconds"
 	depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY
