[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/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__)
 

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;
 

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 */

init/main.c

@@ -47,6 +47,7 @@
 #include <linux/rmap.h>
 #include <linux/mempolicy.h>
 #include <linux/key.h>
+#include <linux/unwind.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -482,6 +483,7 @@ asmlinkage void __init start_kernel(void)
 		   __stop___param - __start___param,
 		   &unknown_bootoption);
 	sort_main_extable();
+	unwind_init();
 	trap_init();
 	rcu_init();
 	init_IRQ();

kernel/Makefile

@@ -21,6 +21,7 @@ obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
 obj-$(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-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_KEXEC) += kexec.o

kernel/module.c

@@ -40,6 +40,7 @@
 #include <linux/string.h>
 #include <linux/sched.h>
 #include <linux/mutex.h>
+#include <linux/unwind.h>
 #include <asm/uaccess.h>
 #include <asm/semaphore.h>
 #include <asm/cacheflush.h>
@@ -1051,6 +1052,8 @@ static void free_module(struct module *mod)
 	remove_sect_attrs(mod);
 	mod_kobject_remove(mod);
 
+	unwind_remove_table(mod->unwind_info, 0);
+
 	/* Arch-specific cleanup. */
 	module_arch_cleanup(mod);
 
@@ -1412,7 +1415,7 @@ static struct module *load_module(void __user *umod,
 	unsigned int i, symindex = 0, strindex = 0, setupindex, exindex,
 		exportindex, modindex, obsparmindex, infoindex, gplindex,
 		crcindex, gplcrcindex, versindex, pcpuindex, gplfutureindex,
-		gplfuturecrcindex;
+		gplfuturecrcindex, unwindex = 0;
 	struct module *mod;
 	long err = 0;
 	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
@@ -1502,6 +1505,9 @@ static struct module *load_module(void __user *umod,
 	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 section */
 	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
@@ -1510,6 +1516,8 @@ static struct module *load_module(void __user *umod,
 	sechdrs[symindex].sh_flags |= SHF_ALLOC;
 	sechdrs[strindex].sh_flags |= SHF_ALLOC;
 #endif
+	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)) {
@@ -1738,6 +1746,11 @@ static struct module *load_module(void __user *umod,
 		goto arch_cleanup;
 	add_sect_attrs(mod, hdr->e_shnum, secstrings, sechdrs);
 
+	/* 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);
 
@@ -1836,6 +1849,7 @@ sys_init_module(void __user *umod,
 	mod->state = MODULE_STATE_LIVE;
 	/* Drop initial reference. */
 	module_put(mod);
+	unwind_remove_table(mod->unwind_info, 1);
 	module_free(mod, mod->module_init);
 	mod->module_init = NULL;
 	mod->init_size = 0;

kernel/unwind.c

@@ -0,0 +1,915 @@
+/*
+ * 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/delay.h>
+#include <linux/stop_machine.h>
+#include <asm/sections.h>
+#include <asm/uaccess.h>
+#include <asm/unaligned.h>
+
+extern char __start_unwind[], __end_unwind[];
+
+#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;
+
+static struct unwind_table {
+	struct {
+		unsigned long pc;
+		unsigned long range;
+	} core, init;
+	const void *address;
+	unsigned long size;
+	struct unwind_table *link;
+	const char *name;
+} root_table, *last_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 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 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)
+{
+	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;
+	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);
+}
+
+/* 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);
+
+	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_run(unlink_table, &info, NR_CPUS);
+
+	if (info.table)
+		kfree(table);
+}
+
+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 unsigned long read_pointer(const u8 **pLoc,
+                                  const void *end,
+                                  signed ptrType)
+{
+	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)
+		return 0;
+	ptr.p8 = *pLoc;
+	switch(ptrType & DW_EH_PE_FORM) {
+	case DW_EH_PE_data2:
+		if (end < (const void *)(ptr.p16u + 1))
+			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))
+			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))
+			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)
+			return 0;
+		break;
+	default:
+		return 0;
+	}
+	switch(ptrType & DW_EH_PE_ADJUST) {
+	case DW_EH_PE_abs:
+		break;
+	case DW_EH_PE_pcrel:
+		value += (unsigned long)*pLoc;
+		break;
+	default:
+		return 0;
+	}
+	if ((ptrType & DW_EH_PE_indirect)
+	    && __get_user(value, (unsigned long *)value))
+		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) || 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:
+				if ((state->loc = read_pointer(&ptr.p8, end, ptrType)) == 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)
+					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
+					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:
+				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)
+			result = 0;
+		if (result && targetLoc != 0 && targetLoc < state->loc)
+			return 1;
+	}
+
+	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 startLoc = 0, endLoc = 0, cfa;
+	unsigned i;
+	signed ptrType = -1;
+	uleb128_t retAddrReg = 0;
+	struct unwind_table *table;
+	struct unwind_state state;
+
+	if (UNW_PC(frame) == 0)
+		return -EINVAL;
+	if ((table = find_table(UNW_PC(frame))) != NULL
+	    && !(table->size & (sizeof(*fde) - 1))) {
+		unsigned long tableSize = table->size;
+
+		for (fde = table->address;
+		     tableSize > sizeof(*fde) && tableSize - sizeof(*fde) >= *fde;
+		     tableSize -= sizeof(*fde) + *fde,
+		     fde += 1 + *fde / sizeof(*fde)) {
+			if (!*fde || (*fde & (sizeof(*fde) - 1)))
+				break;
+			if (!fde[1])
+				continue; /* this is a CIE */
+			if ((fde[1] & (sizeof(*fde) - 1))
+			    || fde[1] > (unsigned long)(fde + 1)
+			                - (unsigned long)table->address)
+				continue; /* 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]
+			    || (ptrType = fde_pointer_type(cie)) < 0) {
+				cie = NULL; /* this is not a (valid) CIE */
+				continue;
+			}
+			ptr = (const u8 *)(fde + 2);
+			startLoc = read_pointer(&ptr,
+			                        (const u8 *)(fde + 1) + *fde,
+			                        ptrType);
+			endLoc = startLoc
+			         + read_pointer(&ptr,
+			                        (const u8 *)(fde + 1) + *fde,
+			                        ptrType & DW_EH_PE_indirect
+			                        ? ptrType
+			                        : ptrType & (DW_EH_PE_FORM|DW_EH_PE_signed));
+			if (UNW_PC(frame) >= startLoc && UNW_PC(frame) < endLoc)
+				break;
+			cie = NULL;
+		}
+	}
+	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;
+		if ((state.version = *ptr) != 1)
+			cie = NULL; /* unsupported version */
+		else if (*++ptr) {
+			/* check if augmentation size is first (and thus present) */
+			if (*ptr == 'z') {
+				/* check for ignorable (or already handled)
+				 * nul-terminated augmentation string */
+				while (++ptr < end && *ptr)
+					if (strchr("LPR", *ptr) == NULL)
+						break;
+			}
+			if (ptr >= end || *ptr)
+				cie = NULL;
+		}
+		++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 {
+			retAddrReg = state.version <= 1 ? *ptr++ : get_uleb128(&ptr, end);
+			/* skip augmentation */
+			if (((const char *)(cie + 2))[1] == 'z')
+				ptr += get_uleb128(&ptr, end);
+			if (ptr > end
+			   || retAddrReg >= ARRAY_SIZE(reg_info)
+			   || REG_INVALID(retAddrReg)
+			   || reg_info[retAddrReg].width != sizeof(unsigned long))
+				cie = NULL;
+		}
+	}
+	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 (cie == NULL || fde == NULL) {
+#ifdef CONFIG_FRAME_POINTER
+		unsigned long top, bottom;
+#endif
+
+#ifdef CONFIG_FRAME_POINTER
+		top = STACK_TOP(frame->task);
+		bottom = STACK_BOTTOM(frame->task);
+# if FRAME_RETADDR_OFFSET < 0
+		if (UNW_SP(frame) < top
+		    && UNW_FP(frame) <= UNW_SP(frame)
+		    && bottom < UNW_FP(frame)
+# else
+		if (UNW_SP(frame) > top
+		    && UNW_FP(frame) >= UNW_SP(frame)
+		    && bottom > UNW_FP(frame)
+# endif
+		   && !((UNW_SP(frame) | UNW_FP(frame))
+		        & (sizeof(unsigned long) - 1))) {
+			unsigned long link;
+
+			if (!__get_user(link,
+			                (unsigned long *)(UNW_FP(frame)
+			                                  + FRAME_LINK_OFFSET))
+# if FRAME_RETADDR_OFFSET < 0
+			   && link > bottom && link < UNW_FP(frame)
+# else
+			   && link > UNW_FP(frame) && link < bottom
+# endif
+			   && !(link & (sizeof(link) - 1))
+			   && !__get_user(UNW_PC(frame),
+			                  (unsigned long *)(UNW_FP(frame)
+			                                    + FRAME_RETADDR_OFFSET))) {
+				UNW_SP(frame) = UNW_FP(frame) + FRAME_RETADDR_OFFSET
+# if FRAME_RETADDR_OFFSET < 0
+					-
+# else
+					+
+# endif
+					  sizeof(UNW_PC(frame));
+				UNW_FP(frame) = link;
+				return 0;
+			}
+		}
+#endif
+		return -ENXIO;
+	}
+	state.org = startLoc;
+	memcpy(&state.cfa, &badCFA, sizeof(state.cfa));
+	/* process instructions */
+	if (!processCFI(ptr, end, UNW_PC(frame), 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)
+	   || state.cfa.offs % sizeof(unsigned long))
+		return -EIO;
+	/* update frame */
+	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
+	for (i = 0; i < ARRAY_SIZE(state.regs); ++i) {
+		if (REG_INVALID(i)) {
+			if (state.regs[i].where == Nowhere)
+				continue;
+			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)
+				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:
+				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:
+				return -EIO;
+			}
+			break;
+		case Value:
+			if (reg_info[i].width != sizeof(unsigned long))
+				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)
+					return -EIO;
+				switch(reg_info[i].width) {
+#define CASE(n)     case sizeof(u##n): \
+					__get_user(FRAME_REG(i, u##n), (u##n *)addr); \
+					break
+				CASES;
+#undef CASE
+				default:
+					return -EIO;
+				}
+			}
+			break;
+		}
+	}
+
+	return 0;
+#undef CASES
+#undef FRAME_REG
+}
+EXPORT_SYMBOL(unwind);
+
+int unwind_init_frame_info(struct unwind_frame_info *info,
+                           struct task_struct *tsk,
+                           /*const*/ struct pt_regs *regs)
+{
+	info->task = tsk;
+	arch_unw_init_frame_info(info, regs);
+
+	return 0;
+}
+EXPORT_SYMBOL(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;
+	arch_unw_init_blocked(info);
+
+	return 0;
+}
+EXPORT_SYMBOL(unwind_init_blocked);
+
+/*
+ * Prepare to unwind the currently running thread.
+ */
+int unwind_init_running(struct unwind_frame_info *info,
+                        asmlinkage void (*callback)(struct unwind_frame_info *,
+                                                    void *arg),
+                        void *arg)
+{
+	info->task = current;
+	arch_unwind_init_running(info, callback, arg);
+
+	return 0;
+}
+EXPORT_SYMBOL(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(unwind_to_user);

lib/Kconfig.debug

@@ -188,14 +188,22 @@ config FRAME_POINTER
 
 config UNWIND_INFO
 	bool "Compile the kernel with frame unwind information"
-	depends on !IA64
-	depends on !MODULES || !(MIPS || PARISC || PPC || SUPERH || V850)
+	depends on !IA64 && !PARISC
+	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 n
+	help
+	  This enables more precise stack traces, omitting all unrelated
+	  occurrences of pointers into kernel code from the dump.
+
 config FORCED_INLINING
 	bool "Force gcc to inline functions marked 'inline'"
 	depends on DEBUG_KERNEL