Re: [PATCH] don't do pointless NULL checks and casts before kfree() in security/

["YOSHIFUJI Hideaki / 吉藤英明" <yoshfuji@linux-ipv6.org>]

In article <200503201331.j2KDVhm12383@blake.inputplus.co.uk> (at Sun, 20 Mar 2005 13:31:43 +0000), Ralph Corderoy <ralph@inputplus.co.uk> says:

> > the short version also have the real bennefits of generating shorter
> > and faster code as well as being shorter "on-screen".
> 
> Faster code?  I'd have thought avoiding the function call outweighed the
> overhead of checking before calling.

Modern CPU can run nicely (expecially with register parameters).
Even if even matters, we can check inline like this:

Signed-off-by: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>

===== include/linux/slab.h 1.40 vs edited =====
--- 1.40/include/linux/slab.h	2005-03-12 05:32:31 +09:00
+++ edited/include/linux/slab.h	2005-03-20 22:47:57 +09:00
@@ -106,8 +106,17 @@
 }
 
 extern void *kcalloc(size_t, size_t, int);
-extern void kfree(const void *);
+extern void __kfree(const void *);
 extern unsigned int ksize(const void *);
+
+static inline void kfree(const void *p)
+{
+#ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE
+	if (!p)
+		return;
+#endif
+	__kfree(p);
+}
 
 extern int FASTCALL(kmem_cache_reap(int));
 extern int FASTCALL(kmem_ptr_validate(kmem_cache_t *cachep, void *ptr));
===== mm/slab.c 1.156 vs edited =====
--- 1.156/mm/slab.c	2005-03-10 17:38:21 +09:00
+++ edited/mm/slab.c	2005-03-20 22:42:45 +09:00
@@ -2561,7 +2561,7 @@
 EXPORT_SYMBOL(kcalloc);
 
 /**
- * kfree - free previously allocated memory
+ * __kfree - free previously allocated memory
  * @objp: pointer returned by kmalloc.
  *
  * Don't free memory not originally allocated by kmalloc()
@@ -2572,8 +2572,10 @@
 	kmem_cache_t *c;
 	unsigned long flags;
 
+#ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
 	if (!objp)
 		return;
+#endif
 	local_irq_save(flags);
 	kfree_debugcheck(objp);
 	c = GET_PAGE_CACHE(virt_to_page(objp));
@@ -2581,7 +2583,7 @@
 	local_irq_restore(flags);
 }
 
-EXPORT_SYMBOL(kfree);
+EXPORT_SYMBOL(__kfree);
 
 #ifdef CONFIG_SMP
 /**