[MiNT] Buggy blockcpy()

[Vincent Rivière <vincent.riviere@freesbee.fr>]

Hello.

Inside FreeMiNT's libkern, I have noticed a very subtle bug in blockcpy() 
for 68000. It had never been triggered because this function is not used.

gas for a.out has a nontrivial bug. It allows sources like:
	bra.s	next
next:
A zero offset is illegal and should be rejected (it is on ELF targets). 
Unfortunately, gas for a.out does not complain and produces invalid code :-(
And this happens in blockcpy() for 68000.

Also, it is obvious that the blockcpy() function has been quickly written 
from a memcpy() implementation. Some code for remaining bytes was still 
here, but obviously useless. I have removed it.

Now this file has been sanitized, I will patch it for ColdFire.

Alan, please commit !

- blockcopy.patch
Fixed 68000 variant and simplified. Contributed by Vincent Riviere.

--
Vincent Rivière

diff -x CVS -aurN freemint.orig/sys/libkern/asm/blockcopy.S freemint/sys/libkern/asm/blockcopy.S
--- freemint.orig/sys/libkern/asm/blockcopy.S	2005-05-07 10:58:16.000000000 +0200
+++ freemint/sys/libkern/asm/blockcopy.S	2011-03-25 00:07:26.812500000 +0100
@@ -16,7 +16,6 @@
 	move.l	_mcpu,d1
 	cmp.w	#40,d1
 	bcc.s	L_040			| for 68000-68030 do quickmove
-	clr.l	d1
 	bra	blkmv
 L_040:	dc.l	0xf6218000		| move16 (a1)+,(a0)+
 	dc.l	0xf6218000
@@ -53,12 +52,9 @@
 	subq.l	#1,d0
 	bne	L_040
 	rts
-#else
-	clr.l	d1
-	bra.s	blkmv
 #endif
 
-blkmv:	movem.l	d1-d7/a2-a6,-(sp)	| save regs
+blkmv:	movem.l	d2-d7/a2-a6,-(sp)	| save regs
 L1:
 	movem.l	(a1)+,d1-d7/a2-a6	| read 12*4 = 48 bytes
 	movem.l	d1-d7/a2-a6,(a0)	|
@@ -85,28 +81,8 @@
 
 	lea	512(a0),a0
 	subq.l	#1,d0
-	bgt.s	L1
+	bne.s	L1
 
-	movem.l	(sp)+,d1-d7/a2-a6	| pop registers
+	movem.l	(sp)+,d2-d7/a2-a6	| pop registers
 
-Leftover:				| do the remaining bytes
-	moveq.l	#3,d0
-	and.w	d1,d0
-	lsr.w	#2,d1
-	subq.w	#1,d1			| prepare for dbra loop
-	bmi.s	L4done
-	lsr.w	#1,d1
-	bcc.s	L23
-L2l:
-	move.l	(a1)+,(a0)+
-L23:
-	move.l	(a1)+,(a0)+
-	dbra	d1,L2l
-L4done:
-	subq.w	#1,d0			| prepare for dbra loop
-	bmi.s	Ldone
-L2:
-	move.b	(a1)+,(a0)+
-	dbra	d0,L2
-Ldone:
 	rts				| return