Subject: [PATCH 1/6] extable: add support for relative extables to search and sort routines

From: [email-masked] (Helge Deller)
Date: Mon, 4 Jan 2016 22:05:07 +0100

On 03.01.2016 17:05, Ard Biesheuvel wrote:
> This adds support to the generic search_extable() and sort_extable()
> implementations for dealing with exception table entries whose fields
> contain relative offsets rather than absolute addresses.
> 
> Signed-off-by: Ard Biesheuvel <[email-masked]>

I tested the generic parts with an upcoming patch which handles relative
exception tables on the parisc platform.
Everything worked as expected.
So for the non arch-relevant changes:
Acked-by: Helge Deller <[email-masked]>

Helge

> ---
>  lib/extable.c | 50 ++++++++++++++++----
>  1 file changed, 41 insertions(+), 9 deletions(-)
> 
> diff --git a/lib/extable.c b/lib/extable.c
> index 4cac81ec225e..0be02ad561e9 100644
> --- a/lib/extable.c
> +++ b/lib/extable.c
> @@ -14,7 +14,37 @@
>  #include <linux/sort.h>
>  #include <asm/uaccess.h>
>  
> +#ifndef ARCH_HAS_RELATIVE_EXTABLE
> +#define ex_to_insn(x)	((x)->insn)
> +#else
> +static inline unsigned long ex_to_insn(const struct exception_table_entry *x)
> +{
> +	return (unsigned long)&x->insn + x->insn;
> +}
> +#endif
> +
>  #ifndef ARCH_HAS_SORT_EXTABLE
> +#ifndef ARCH_HAS_RELATIVE_EXTABLE
> +#define swap_ex		NULL
> +#else
> +static void swap_ex(void *a, void *b, int size)
> +{
> +	struct exception_table_entry *x = a, *y = b, tmp;
> +	int delta = b - a;
> +
> +	tmp = *x;
> +	x->insn = y->insn + delta;
> +	y->insn = tmp.insn - delta;
> +
> +#ifdef swap_ex_entry_fixup
> +	swap_ex_entry_fixup(x, y, tmp, delta);
> +#else
> +	x->fixup = y->fixup + delta;
> +	y->fixup = tmp.fixup - delta;
> +#endif
> +}
> +#endif /* ARCH_HAS_RELATIVE_EXTABLE */
> +
>  /*
>   * The exception table needs to be sorted so that the binary
>   * search that we use to find entries in it works properly.
> @@ -26,9 +56,9 @@ static int cmp_ex(const void *a, const void *b)
>  	const struct exception_table_entry *x = a, *y = b;
>  
>  	/* avoid overflow */
> -	if (x->insn > y->insn)
> +	if (ex_to_insn(x) > ex_to_insn(y))
>  		return 1;
> -	if (x->insn < y->insn)
> +	if (ex_to_insn(x) < ex_to_insn(y))
>  		return -1;
>  	return 0;
>  }
> @@ -37,7 +67,7 @@ void sort_extable(struct exception_table_entry *start,
>  		  struct exception_table_entry *finish)
>  {
>  	sort(start, finish - start, sizeof(struct exception_table_entry),
> -	     cmp_ex, NULL);
> +	     cmp_ex, swap_ex);
>  }
>  
>  #ifdef CONFIG_MODULES
> @@ -48,13 +78,15 @@ void sort_extable(struct exception_table_entry *start,
>  void trim_init_extable(struct module *m)
>  {
>  	/*trim the beginning*/
> -	while (m->num_exentries && within_module_init(m->extable[0].insn, m)) {
> +	while (m->num_exentries &&
> +	       within_module_init(ex_to_insn(&m->extable[0]), m)) {
>  		m->extable++;
>  		m->num_exentries--;
>  	}
>  	/*trim the end*/
>  	while (m->num_exentries &&
> -		within_module_init(m->extable[m->num_exentries-1].insn, m))
> +	       within_module_init(ex_to_insn(&m->extable[m->num_exentries - 1]),
> +				  m))
>  		m->num_exentries--;
>  }
>  #endif /* CONFIG_MODULES */
> @@ -81,13 +113,13 @@ search_extable(const struct exception_table_entry *first,
>  		 * careful, the distance between value and insn
>  		 * can be larger than MAX_LONG:
>  		 */
> -		if (mid->insn < value)
> +		if (ex_to_insn(mid) < value)
>  			first = mid + 1;
> -		else if (mid->insn > value)
> +		else if (ex_to_insn(mid) > value)
>  			last = mid - 1;
>  		else
>  			return mid;
> -        }
> -        return NULL;
> +	}
> +	return NULL;
>  }
>  #endif
>