Patchwork ARM: fix unwinding for XIP kernels

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Submitter Uwe Kleine-König
Date Nov. 30, 2011, 7:07 p.m.
Message ID <1322680072-14269-1-git-send-email-u.kleine-koenig@pengutronix.de>
Download mbox | patch
Permalink /patch/128554/
State New
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Comments

Uwe Kleine-König - Nov. 30, 2011, 7:07 p.m.
The linker places the unwind tables in readonly sections. So when using
an XIP kernel these are located in ROM and cannot be modified.
For that reason the current approach to convert the relative offsets in
the unwind index to absolute addresses early in the boot process doesn't
work with XIP.

The offsets in the unwind index section are signed 31 bit numbers and
the structs are sorted by this offset. So it first has offsets between
0x40000000 and 0x7fffffff (i.e. the negative offsets) and then offsets
between 0x00000000 and 0x3fffffff. When seperating these two blocks the
numbers are sorted even when interpreting the offsets as unsigned longs.

So determine the first non-negative entry once and track that using the
new origin pointer. The actual bisection can then use a plain unsigned
long comparison. The only thing that makes the new bisection more
complicated is that the offsets are relative to their position in the
index section, so the key to search needs to be adapted accordingly in
each step.

Moreover several consts are added to catch future writes and rename the
member "addr" of struct unwind_idx to "addr_offset" to better match the
new semantic. (This has the additional benefit of breaking eventual
users at compile time to make them aware of the change.)

In my tests the new algorithm was a tad faster than the original and has
the additional upside of not needing the initial conversion and so saves
some boot time and it's possible to unwind even earlier.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
Hello,

the code is the same as the two previous patches combined, only some
whitespace changes.

There are a few checkpatch issues left, namely one line over 80 chars
(which was already there before and IMHO is ok) and two warnings about
externs in arch/arm/kernel/unwind.c (__start_unwind_idx and
__stop_unwind_idx) which are ok, too. These externs were there before
and only the unwinder should care about them.

Thanks to Catalin to take the time to review my work.

Best regards
Uwe

 arch/arm/include/asm/unwind.h |   16 +----
 arch/arm/kernel/setup.c       |    2 -
 arch/arm/kernel/unwind.c      |  129 ++++++++++++++++++++++++++--------------
 3 files changed, 88 insertions(+), 59 deletions(-)
Nicolas Pitre - Nov. 30, 2011, 7:37 p.m.
On Wed, 30 Nov 2011, Uwe Kleine-König wrote:

> The linker places the unwind tables in readonly sections. So when using
> an XIP kernel these are located in ROM and cannot be modified.
> For that reason the current approach to convert the relative offsets in
> the unwind index to absolute addresses early in the boot process doesn't
> work with XIP.
> 
> The offsets in the unwind index section are signed 31 bit numbers and
> the structs are sorted by this offset. So it first has offsets between
> 0x40000000 and 0x7fffffff (i.e. the negative offsets) and then offsets
> between 0x00000000 and 0x3fffffff. When seperating these two blocks the
> numbers are sorted even when interpreting the offsets as unsigned longs.
> 
> So determine the first non-negative entry once and track that using the
> new origin pointer. The actual bisection can then use a plain unsigned
> long comparison. The only thing that makes the new bisection more
> complicated is that the offsets are relative to their position in the
> index section, so the key to search needs to be adapted accordingly in
> each step.
> 
> Moreover several consts are added to catch future writes and rename the
> member "addr" of struct unwind_idx to "addr_offset" to better match the
> new semantic. (This has the additional benefit of breaking eventual
> users at compile time to make them aware of the change.)
> 
> In my tests the new algorithm was a tad faster than the original and has
> the additional upside of not needing the initial conversion and so saves
> some boot time and it's possible to unwind even earlier.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Nicolas Pitre <nico@fluxnic.net>

Acked-by: Nicolas Pitre <nico@linaro.org>

> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
> Hello,
> 
> the code is the same as the two previous patches combined, only some
> whitespace changes.
> 
> There are a few checkpatch issues left, namely one line over 80 chars
> (which was already there before and IMHO is ok) and two warnings about
> externs in arch/arm/kernel/unwind.c (__start_unwind_idx and
> __stop_unwind_idx) which are ok, too. These externs were there before
> and only the unwinder should care about them.
> 
> Thanks to Catalin to take the time to review my work.
> 
> Best regards
> Uwe
> 
>  arch/arm/include/asm/unwind.h |   16 +----
>  arch/arm/kernel/setup.c       |    2 -
>  arch/arm/kernel/unwind.c      |  129 ++++++++++++++++++++++++++--------------
>  3 files changed, 88 insertions(+), 59 deletions(-)
> 
> diff --git a/arch/arm/include/asm/unwind.h b/arch/arm/include/asm/unwind.h
> index a5edf42..d1c3f3a 100644
> --- a/arch/arm/include/asm/unwind.h
> +++ b/arch/arm/include/asm/unwind.h
> @@ -30,14 +30,15 @@ enum unwind_reason_code {
>  };
>  
>  struct unwind_idx {
> -	unsigned long addr;
> +	unsigned long addr_offset;
>  	unsigned long insn;
>  };
>  
>  struct unwind_table {
>  	struct list_head list;
> -	struct unwind_idx *start;
> -	struct unwind_idx *stop;
> +	const struct unwind_idx *start;
> +	const struct unwind_idx *origin;
> +	const struct unwind_idx *stop;
>  	unsigned long begin_addr;
>  	unsigned long end_addr;
>  };
> @@ -49,15 +50,6 @@ extern struct unwind_table *unwind_table_add(unsigned long start,
>  extern void unwind_table_del(struct unwind_table *tab);
>  extern void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk);
>  
> -#ifdef CONFIG_ARM_UNWIND
> -extern int __init unwind_init(void);
> -#else
> -static inline int __init unwind_init(void)
> -{
> -	return 0;
> -}
> -#endif
> -
>  #endif	/* !__ASSEMBLY__ */
>  
>  #ifdef CONFIG_ARM_UNWIND
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 7e7977a..cf9d71a 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -893,8 +893,6 @@ void __init setup_arch(char **cmdline_p)
>  {
>  	struct machine_desc *mdesc;
>  
> -	unwind_init();
> -
>  	setup_processor();
>  	mdesc = setup_machine_fdt(__atags_pointer);
>  	if (!mdesc)
> diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
> index e7e8365..3f03fe0 100644
> --- a/arch/arm/kernel/unwind.c
> +++ b/arch/arm/kernel/unwind.c
> @@ -67,7 +67,7 @@ EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
>  
>  struct unwind_ctrl_block {
>  	unsigned long vrs[16];		/* virtual register set */
> -	unsigned long *insn;		/* pointer to the current instructions word */
> +	const unsigned long *insn;	/* pointer to the current instructions word */
>  	int entries;			/* number of entries left to interpret */
>  	int byte;			/* current byte number in the instructions word */
>  };
> @@ -83,8 +83,9 @@ enum regs {
>  	PC = 15
>  };
>  
> -extern struct unwind_idx __start_unwind_idx[];
> -extern struct unwind_idx __stop_unwind_idx[];
> +extern const struct unwind_idx __start_unwind_idx[];
> +static const struct unwind_idx *__origin_unwind_idx;
> +extern const struct unwind_idx __stop_unwind_idx[];
>  
>  static DEFINE_SPINLOCK(unwind_lock);
>  static LIST_HEAD(unwind_tables);
> @@ -98,45 +99,99 @@ static LIST_HEAD(unwind_tables);
>  })
>  
>  /*
> - * Binary search in the unwind index. The entries entries are
> + * Binary search in the unwind index. The entries are
>   * guaranteed to be sorted in ascending order by the linker.
> + *
> + * start = first entry
> + * origin = first entry with positive offset (or stop if there is no such entry)
> + * stop - 1 = last entry
>   */
> -static struct unwind_idx *search_index(unsigned long addr,
> -				       struct unwind_idx *first,
> -				       struct unwind_idx *last)
> +static const struct unwind_idx *search_index(unsigned long addr,
> +				       const struct unwind_idx *start,
> +				       const struct unwind_idx *origin,
> +				       const struct unwind_idx *stop)
>  {
> -	pr_debug("%s(%08lx, %p, %p)\n", __func__, addr, first, last);
> +	unsigned long addr_prel31;
> +
> +	pr_debug("%s(%08lx, %p, %p, %p)\n",
> +			__func__, addr, start, origin, stop);
> +
> +	/*
> +	 * only search in the section with the matching sign. This way the
> +	 * prel31 numbers can be compared as unsigned longs.
> +	 */
> +	if (addr < (unsigned long)start)
> +		/* negative offsets: [start; origin) */
> +		stop = origin;
> +	else
> +		/* positive offsets: [origin; stop) */
> +		start = origin;
> +
> +	/* prel31 for address relavive to start */
> +	addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;
>  
> -	if (addr < first->addr) {
> +	while (start < stop - 1) {
> +		const struct unwind_idx *mid = start + ((stop - start) >> 1);
> +
> +		/*
> +		 * As addr_prel31 is relative to start an offset is needed to
> +		 * make it relative to mid.
> +		 */
> +		if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
> +				mid->addr_offset)
> +			stop = mid;
> +		else {
> +			/* keep addr_prel31 relative to start */
> +			addr_prel31 -= ((unsigned long)mid -
> +					(unsigned long)start);
> +			start = mid;
> +		}
> +	}
> +
> +	if (likely(start->addr_offset <= addr_prel31))
> +		return start;
> +	else {
>  		pr_warning("unwind: Unknown symbol address %08lx\n", addr);
>  		return NULL;
> -	} else if (addr >= last->addr)
> -		return last;
> +	}
> +}
>  
> -	while (first < last - 1) {
> -		struct unwind_idx *mid = first + ((last - first + 1) >> 1);
> +static const struct unwind_idx *unwind_find_origin(
> +		const struct unwind_idx *start, const struct unwind_idx *stop)
> +{
> +	pr_debug("%s(%p, %p)\n", __func__, start, stop);
> +	while (start < stop - 1) {
> +		const struct unwind_idx *mid = start + ((stop - start) >> 1);
>  
> -		if (addr < mid->addr)
> -			last = mid;
> +		if (mid->addr_offset >= 0x40000000)
> +			/* negative offset */
> +			start = mid;
>  		else
> -			first = mid;
> +			/* positive offset */
> +			stop = mid;
>  	}
> -
> -	return first;
> +	pr_debug("%s -> %p\n", __func__, stop);
> +	return stop;
>  }
>  
> -static struct unwind_idx *unwind_find_idx(unsigned long addr)
> +static const struct unwind_idx *unwind_find_idx(unsigned long addr)
>  {
> -	struct unwind_idx *idx = NULL;
> +	const struct unwind_idx *idx = NULL;
>  	unsigned long flags;
>  
>  	pr_debug("%s(%08lx)\n", __func__, addr);
>  
> -	if (core_kernel_text(addr))
> +	if (core_kernel_text(addr)) {
> +		if (unlikely(!__origin_unwind_idx))
> +			__origin_unwind_idx =
> +				unwind_find_origin(__start_unwind_idx,
> +						__stop_unwind_idx);
> +
>  		/* main unwind table */
>  		idx = search_index(addr, __start_unwind_idx,
> -				   __stop_unwind_idx - 1);
> -	else {
> +				   __origin_unwind_idx,
> +				   __stop_unwind_idx);
> +	} else {
>  		/* module unwind tables */
>  		struct unwind_table *table;
>  
> @@ -145,7 +200,8 @@ static struct unwind_idx *unwind_find_idx(unsigned long addr)
>  			if (addr >= table->begin_addr &&
>  			    addr < table->end_addr) {
>  				idx = search_index(addr, table->start,
> -						   table->stop - 1);
> +						   table->origin,
> +						   table->stop);
>  				/* Move-to-front to exploit common traces */
>  				list_move(&table->list, &unwind_tables);
>  				break;
> @@ -274,7 +330,7 @@ static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
>  int unwind_frame(struct stackframe *frame)
>  {
>  	unsigned long high, low;
> -	struct unwind_idx *idx;
> +	const struct unwind_idx *idx;
>  	struct unwind_ctrl_block ctrl;
>  
>  	/* only go to a higher address on the stack */
> @@ -399,7 +455,6 @@ struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
>  				      unsigned long text_size)
>  {
>  	unsigned long flags;
> -	struct unwind_idx *idx;
>  	struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
>  
>  	pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
> @@ -408,15 +463,12 @@ struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
>  	if (!tab)
>  		return tab;
>  
> -	tab->start = (struct unwind_idx *)start;
> -	tab->stop = (struct unwind_idx *)(start + size);
> +	tab->start = (const struct unwind_idx *)start;
> +	tab->stop = (const struct unwind_idx *)(start + size);
> +	tab->origin = unwind_find_origin(tab->start, tab->stop);
>  	tab->begin_addr = text_addr;
>  	tab->end_addr = text_addr + text_size;
>  
> -	/* Convert the symbol addresses to absolute values */
> -	for (idx = tab->start; idx < tab->stop; idx++)
> -		idx->addr = prel31_to_addr(&idx->addr);
> -
>  	spin_lock_irqsave(&unwind_lock, flags);
>  	list_add_tail(&tab->list, &unwind_tables);
>  	spin_unlock_irqrestore(&unwind_lock, flags);
> @@ -437,16 +489,3 @@ void unwind_table_del(struct unwind_table *tab)
>  
>  	kfree(tab);
>  }
> -
> -int __init unwind_init(void)
> -{
> -	struct unwind_idx *idx;
> -
> -	/* Convert the symbol addresses to absolute values */
> -	for (idx = __start_unwind_idx; idx < __stop_unwind_idx; idx++)
> -		idx->addr = prel31_to_addr(&idx->addr);
> -
> -	pr_debug("unwind: ARM stack unwinding initialised\n");
> -
> -	return 0;
> -}
> -- 
> 1.7.7.2
>
Catalin Marinas - Nov. 30, 2011, 7:52 p.m.
2011/11/30 Uwe Kleine-König <u.kleine-koenig@pengutronix.de>:
> The linker places the unwind tables in readonly sections. So when using
> an XIP kernel these are located in ROM and cannot be modified.
> For that reason the current approach to convert the relative offsets in
> the unwind index to absolute addresses early in the boot process doesn't
> work with XIP.
>
> The offsets in the unwind index section are signed 31 bit numbers and
> the structs are sorted by this offset. So it first has offsets between
> 0x40000000 and 0x7fffffff (i.e. the negative offsets) and then offsets
> between 0x00000000 and 0x3fffffff. When seperating these two blocks the
> numbers are sorted even when interpreting the offsets as unsigned longs.
>
> So determine the first non-negative entry once and track that using the
> new origin pointer. The actual bisection can then use a plain unsigned
> long comparison. The only thing that makes the new bisection more
> complicated is that the offsets are relative to their position in the
> index section, so the key to search needs to be adapted accordingly in
> each step.
>
> Moreover several consts are added to catch future writes and rename the
> member "addr" of struct unwind_idx to "addr_offset" to better match the
> new semantic. (This has the additional benefit of breaking eventual
> users at compile time to make them aware of the change.)
>
> In my tests the new algorithm was a tad faster than the original and has
> the additional upside of not needing the initial conversion and so saves
> some boot time and it's possible to unwind even earlier.
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Nicolas Pitre <nico@fluxnic.net>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Patch

diff --git a/arch/arm/include/asm/unwind.h b/arch/arm/include/asm/unwind.h
index a5edf42..d1c3f3a 100644
--- a/arch/arm/include/asm/unwind.h
+++ b/arch/arm/include/asm/unwind.h
@@ -30,14 +30,15 @@  enum unwind_reason_code {
 };
 
 struct unwind_idx {
-	unsigned long addr;
+	unsigned long addr_offset;
 	unsigned long insn;
 };
 
 struct unwind_table {
 	struct list_head list;
-	struct unwind_idx *start;
-	struct unwind_idx *stop;
+	const struct unwind_idx *start;
+	const struct unwind_idx *origin;
+	const struct unwind_idx *stop;
 	unsigned long begin_addr;
 	unsigned long end_addr;
 };
@@ -49,15 +50,6 @@  extern struct unwind_table *unwind_table_add(unsigned long start,
 extern void unwind_table_del(struct unwind_table *tab);
 extern void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk);
 
-#ifdef CONFIG_ARM_UNWIND
-extern int __init unwind_init(void);
-#else
-static inline int __init unwind_init(void)
-{
-	return 0;
-}
-#endif
-
 #endif	/* !__ASSEMBLY__ */
 
 #ifdef CONFIG_ARM_UNWIND
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 7e7977a..cf9d71a 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -893,8 +893,6 @@  void __init setup_arch(char **cmdline_p)
 {
 	struct machine_desc *mdesc;
 
-	unwind_init();
-
 	setup_processor();
 	mdesc = setup_machine_fdt(__atags_pointer);
 	if (!mdesc)
diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index e7e8365..3f03fe0 100644
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -67,7 +67,7 @@  EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
 
 struct unwind_ctrl_block {
 	unsigned long vrs[16];		/* virtual register set */
-	unsigned long *insn;		/* pointer to the current instructions word */
+	const unsigned long *insn;	/* pointer to the current instructions word */
 	int entries;			/* number of entries left to interpret */
 	int byte;			/* current byte number in the instructions word */
 };
@@ -83,8 +83,9 @@  enum regs {
 	PC = 15
 };
 
-extern struct unwind_idx __start_unwind_idx[];
-extern struct unwind_idx __stop_unwind_idx[];
+extern const struct unwind_idx __start_unwind_idx[];
+static const struct unwind_idx *__origin_unwind_idx;
+extern const struct unwind_idx __stop_unwind_idx[];
 
 static DEFINE_SPINLOCK(unwind_lock);
 static LIST_HEAD(unwind_tables);
@@ -98,45 +99,99 @@  static LIST_HEAD(unwind_tables);
 })
 
 /*
- * Binary search in the unwind index. The entries entries are
+ * Binary search in the unwind index. The entries are
  * guaranteed to be sorted in ascending order by the linker.
+ *
+ * start = first entry
+ * origin = first entry with positive offset (or stop if there is no such entry)
+ * stop - 1 = last entry
  */
-static struct unwind_idx *search_index(unsigned long addr,
-				       struct unwind_idx *first,
-				       struct unwind_idx *last)
+static const struct unwind_idx *search_index(unsigned long addr,
+				       const struct unwind_idx *start,
+				       const struct unwind_idx *origin,
+				       const struct unwind_idx *stop)
 {
-	pr_debug("%s(%08lx, %p, %p)\n", __func__, addr, first, last);
+	unsigned long addr_prel31;
+
+	pr_debug("%s(%08lx, %p, %p, %p)\n",
+			__func__, addr, start, origin, stop);
+
+	/*
+	 * only search in the section with the matching sign. This way the
+	 * prel31 numbers can be compared as unsigned longs.
+	 */
+	if (addr < (unsigned long)start)
+		/* negative offsets: [start; origin) */
+		stop = origin;
+	else
+		/* positive offsets: [origin; stop) */
+		start = origin;
+
+	/* prel31 for address relavive to start */
+	addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;
 
-	if (addr < first->addr) {
+	while (start < stop - 1) {
+		const struct unwind_idx *mid = start + ((stop - start) >> 1);
+
+		/*
+		 * As addr_prel31 is relative to start an offset is needed to
+		 * make it relative to mid.
+		 */
+		if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
+				mid->addr_offset)
+			stop = mid;
+		else {
+			/* keep addr_prel31 relative to start */
+			addr_prel31 -= ((unsigned long)mid -
+					(unsigned long)start);
+			start = mid;
+		}
+	}
+
+	if (likely(start->addr_offset <= addr_prel31))
+		return start;
+	else {
 		pr_warning("unwind: Unknown symbol address %08lx\n", addr);
 		return NULL;
-	} else if (addr >= last->addr)
-		return last;
+	}
+}
 
-	while (first < last - 1) {
-		struct unwind_idx *mid = first + ((last - first + 1) >> 1);
+static const struct unwind_idx *unwind_find_origin(
+		const struct unwind_idx *start, const struct unwind_idx *stop)
+{
+	pr_debug("%s(%p, %p)\n", __func__, start, stop);
+	while (start < stop - 1) {
+		const struct unwind_idx *mid = start + ((stop - start) >> 1);
 
-		if (addr < mid->addr)
-			last = mid;
+		if (mid->addr_offset >= 0x40000000)
+			/* negative offset */
+			start = mid;
 		else
-			first = mid;
+			/* positive offset */
+			stop = mid;
 	}
-
-	return first;
+	pr_debug("%s -> %p\n", __func__, stop);
+	return stop;
 }
 
-static struct unwind_idx *unwind_find_idx(unsigned long addr)
+static const struct unwind_idx *unwind_find_idx(unsigned long addr)
 {
-	struct unwind_idx *idx = NULL;
+	const struct unwind_idx *idx = NULL;
 	unsigned long flags;
 
 	pr_debug("%s(%08lx)\n", __func__, addr);
 
-	if (core_kernel_text(addr))
+	if (core_kernel_text(addr)) {
+		if (unlikely(!__origin_unwind_idx))
+			__origin_unwind_idx =
+				unwind_find_origin(__start_unwind_idx,
+						__stop_unwind_idx);
+
 		/* main unwind table */
 		idx = search_index(addr, __start_unwind_idx,
-				   __stop_unwind_idx - 1);
-	else {
+				   __origin_unwind_idx,
+				   __stop_unwind_idx);
+	} else {
 		/* module unwind tables */
 		struct unwind_table *table;
 
@@ -145,7 +200,8 @@  static struct unwind_idx *unwind_find_idx(unsigned long addr)
 			if (addr >= table->begin_addr &&
 			    addr < table->end_addr) {
 				idx = search_index(addr, table->start,
-						   table->stop - 1);
+						   table->origin,
+						   table->stop);
 				/* Move-to-front to exploit common traces */
 				list_move(&table->list, &unwind_tables);
 				break;
@@ -274,7 +330,7 @@  static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
 int unwind_frame(struct stackframe *frame)
 {
 	unsigned long high, low;
-	struct unwind_idx *idx;
+	const struct unwind_idx *idx;
 	struct unwind_ctrl_block ctrl;
 
 	/* only go to a higher address on the stack */
@@ -399,7 +455,6 @@  struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
 				      unsigned long text_size)
 {
 	unsigned long flags;
-	struct unwind_idx *idx;
 	struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
 
 	pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
@@ -408,15 +463,12 @@  struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
 	if (!tab)
 		return tab;
 
-	tab->start = (struct unwind_idx *)start;
-	tab->stop = (struct unwind_idx *)(start + size);
+	tab->start = (const struct unwind_idx *)start;
+	tab->stop = (const struct unwind_idx *)(start + size);
+	tab->origin = unwind_find_origin(tab->start, tab->stop);
 	tab->begin_addr = text_addr;
 	tab->end_addr = text_addr + text_size;
 
-	/* Convert the symbol addresses to absolute values */
-	for (idx = tab->start; idx < tab->stop; idx++)
-		idx->addr = prel31_to_addr(&idx->addr);
-
 	spin_lock_irqsave(&unwind_lock, flags);
 	list_add_tail(&tab->list, &unwind_tables);
 	spin_unlock_irqrestore(&unwind_lock, flags);
@@ -437,16 +489,3 @@  void unwind_table_del(struct unwind_table *tab)
 
 	kfree(tab);
 }
-
-int __init unwind_init(void)
-{
-	struct unwind_idx *idx;
-
-	/* Convert the symbol addresses to absolute values */
-	for (idx = __start_unwind_idx; idx < __stop_unwind_idx; idx++)
-		idx->addr = prel31_to_addr(&idx->addr);
-
-	pr_debug("unwind: ARM stack unwinding initialised\n");
-
-	return 0;
-}