RE: [Linux-ia64] Re: memcpy failure

["Chen, Kenneth W" <kenneth.w.chen@intel.com>]

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Here is the patch that I promised.

Bjorn, would you please apply it to the 2.4 tree? and
David, would you please apply it to the 2.5 tree?

Thanks.

- Ken


-----Original Message-----
From: Chen, Kenneth W 
Sent: Thursday, November 14, 2002 7:53 AM
To: Matthew Wilcox; Christian Cotte-Barrot
Cc: linux-ia64@linuxia64.org
Subject: RE: [Linux-ia64] Re: memcpy failure



> >On Thu, Nov 14, 2002 at 10:01:44AM +0100, Christian Cotte-Barrot wrote:
> > But memcpy from memcpy.S is returning a pointer to dest area.
> > That would lead to quasi non-portable code when the return from memcopy
> > is correctly checked depending on which memcopy function is addressed.
> > But BTW, is it meaningful to take into account a return code
> > that is always the same and which value is known in advance ?
> > Does memcpy suppose to failed in some cases ?

> no, memcpy cannot fail (you get a SIGSEGV in userspace or an MCA in
> kernel space).  checking the return value is meaningless.

That's what I feel as well that it is kind of silly to return something that the caller already has. BUt then, I'm not here to judge the specification ;-)

Anyhow, the fix is fairly easy and won't affect the code size as well as the copy throughput, I should have a patch ready shortly to make everyone happy!

- Ken

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[-- Attachment #2: memcpy_mck.fix.patch --]
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--- linux/arch/ia64/lib/memcpy_mck.S.orig	Fri Nov  8 18:05:05 2002
+++ linux/arch/ia64/lib/memcpy_mck.S	Thu Nov 14 11:33:53 2002
@@ -6,7 +6,10 @@
  *	in1:	source address
  *	in2:	number of bytes to copy
  * Output:
- * 	0 if success, or number of byte NOT copied if error occurred.
+ *	for bcopy:     return nothing
+ *	for memcpy:    retrun dest
+ * 	for copy_user: return 0 if success,
+ *		       or number of byte NOT copied if error occurred.
  *
  * Copyright (C) 2002 Intel Corp.
  * Copyright (C) 2002 Ken Chen <kenneth.w.chen@intel.com>
@@ -86,6 +89,7 @@
 	and	r28=0x7,in0
 	and	r29=0x7,in1
 	mov	f6=f0
+	mov	retval=in0
 	br.cond.sptk .common_code
 	;;
 END(memcpy)
@@ -97,7 +101,7 @@
 	mov	f6=f1
 	mov	saved_in0=in0	// save dest pointer
 	mov	saved_in1=in1	// save src pointer
-	mov	saved_in2=in2	// save len
+	mov	retval=r0	// initialize return value
 	;;
 .common_code:
 	cmp.gt	p15,p0=8,in2	// check for small size
@@ -105,7 +109,7 @@
 	cmp.ne	p14,p0=0,r29	// check src alignment
 	add	src0=0,in1
 	sub	r30=8,r28	// for .align_dest
-	mov	retval=r0	// initialize return value
+	mov	saved_in2=in2	// save len
 	;;
 	add	dst0=0,in0
 	add	dst1=1,in0	// dest odd index