linux-kernel - [PATCH v2] lib/extable.c: use bsearch() library function in search

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Message-ID: <1496529521.2534.4.camel@m3y3r.de>
Date:   Sun, 04 Jun 2017 00:38:41 +0200
From:   Thomas Meyer <thomas@...3r.de>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] lib/extable.c: use bsearch() library function in
 search_extable()

Signed-off-by: Thomas Meyer <thomas@...3r.de>
---
 include/linux/extable.h |  3 ++-
 kernel/extable.c        |  2 +-
 kernel/module.c         |  2 +-
 lib/extable.c           | 38 +++++++++++++++++++-------------------
 4 files changed, 23 insertions(+), 22 deletions(-)

diff --git a/include/linux/extable.h b/include/linux/extable.h
index 7effea4..b575bb9 100644
--- a/include/linux/extable.h
+++ b/include/linux/extable.h
@@ -2,13 +2,14 @@
 #define _LINUX_EXTABLE_H
 
 #include <linux/stddef.h>	/* for NULL */
+#include <linux/types.h>
 
 struct module;
 struct exception_table_entry;
 
 const struct exception_table_entry *
 search_extable(const struct exception_table_entry *first,
-	       const struct exception_table_entry *last,
+	       const size_t num,
 	       unsigned long value);
 void sort_extable(struct exception_table_entry *start,
 		  struct exception_table_entry *finish);
diff --git a/kernel/extable.c b/kernel/extable.c
index 2676d7f..0c25b75 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -55,7 +55,7 @@ const struct exception_table_entry *search_exception_tables(unsigned long addr)
 {
 	const struct exception_table_entry *e;
 
-	e = search_extable(__start___ex_table, __stop___ex_table-1, addr);
+	e = search_extable(__start___ex_table, __stop___ex_table - __start___ex_table, addr);
 	if (!e)
 		e = search_module_extables(addr);
 	return e;
diff --git a/kernel/module.c b/kernel/module.c
index 4a3665f..22faf11 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4201,7 +4201,7 @@ const struct exception_table_entry *search_module_extables(unsigned long addr)
 		goto out;
 
 	e = search_extable(mod->extable,
-			   mod->extable + mod->num_exentries - 1,
+			   mod->num_exentries,
 			   addr);
 out:
 	preempt_enable();
diff --git a/lib/extable.c b/lib/extable.c
index 62968da..d4d3929 100644
--- a/lib/extable.c
+++ b/lib/extable.c
@@ -9,6 +9,7 @@
  * 2 of the License, or (at your option) any later version.
  */
 
+#include <linux/bsearch.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/sort.h>
@@ -51,7 +52,7 @@ static void swap_ex(void *a, void *b, int size)
  * This is used both for the kernel exception table and for
  * the exception tables of modules that get loaded.
  */
-static int cmp_ex(const void *a, const void *b)
+static int cmp_ex_sort(const void *a, const void *b)
 {
 	const struct exception_table_entry *x = a, *y = b;
 
@@ -67,7 +68,7 @@ void sort_extable(struct exception_table_entry *start,
 		  struct exception_table_entry *finish)
 {
 	sort(start, finish - start, sizeof(struct exception_table_entry),
-	     cmp_ex, swap_ex);
+	     cmp_ex_sort, swap_ex);
 }
 
 #ifdef CONFIG_MODULES
@@ -93,6 +94,20 @@ void trim_init_extable(struct module *m)
 #endif /* !ARCH_HAS_SORT_EXTABLE */
 
 #ifndef ARCH_HAS_SEARCH_EXTABLE
+
+static int cmp_ex_search(const void *key, const void *elt)
+{
+	const struct exception_table_entry * _elt = elt;
+	unsigned long k = *(unsigned long*) key;
+
+	/* avoid overflow */
+	if (k > ex_to_insn(_elt))
+		return 1;
+	if (k < ex_to_insn(_elt))
+		return -1;
+	return 0;
+}
+
 /*
  * Search one exception table for an entry corresponding to the
  * given instruction address, and return the address of the entry,
@@ -102,24 +117,9 @@ void trim_init_extable(struct module *m)
  */
 const struct exception_table_entry *
 search_extable(const struct exception_table_entry *first,
-	       const struct exception_table_entry *last,
+	       const size_t num, 
 	       unsigned long value)
 {
-	while (first <= last) {
-		const struct exception_table_entry *mid;
-
-		mid = ((last - first) >> 1) + first;
-		/*
-		 * careful, the distance between value and insn
-		 * can be larger than MAX_LONG:
-		 */
-		if (ex_to_insn(mid) < value)
-			first = mid + 1;
-		else if (ex_to_insn(mid) > value)
-			last = mid - 1;
-		else
-			return mid;
-	}
-	return NULL;
+	return bsearch(&value, first, num, sizeof(struct exception_table_entry), cmp_ex_search);
 }
 #endif