--- /sys/src/9/vt4/fns.h	Thu May 29 00:00:00 2014
+++ /sys/src/9/vt4/fns.h	Thu May 29 00:00:00 2014
@@ -44,7 +44,6 @@
 void	dump(void *, int);
 void	eieio(void);
 void	etherclock(void);
-void	evenaddr(uintptr);
 void	fifoinit(Ether *);
 void	firmware(int);
 int	fpipower(Ureg*);
@@ -169,6 +168,7 @@
 void	uncinit(void);
 void	uncinitwait(void);
 #define	userureg(ur)	(((ur)->status & MSR_PR) != 0)
+void	validalign(uintptr, unsigned);
 void	verifyproc(Proc *);
 void	verifymach(Mach *);
 #define	waserror()	(up->nerrlab++, setlabel(&up->errlab[up->nerrlab-1]))
--- /sys/src/9/vt4/syscall.c	Thu May 29 00:00:00 2014
+++ /sys/src/9/vt4/syscall.c	Thu May 29 00:00:00 2014
@@ -275,15 +275,32 @@
 }
 
 /*
- * called in sysfile.c
+ * called in syscallfmt.c, sysfile.c, sysproc.c
  */
 void
-evenaddr(uintptr addr)
+validalign(uintptr addr, unsigned align)
 {
-	if(addr & (sizeof(uintptr)-1)){
-		postnote(up, 1, "sys: misaligned address", NDebug);
-		error(Ebadarg);
-	}
+	/*
+	 * Plan 9 is a 32-bit O/S, and the hardware it runs on
+	 * does not usually have instructions which move 64-bit
+	 * quantities directly, synthesizing the operations
+	 * with 32-bit move instructions. Therefore, the compiler
+	 * (and hardware) usually only enforce 32-bit alignment,
+	 * if at all.
+	 *
+	 * Take this out if the architecture warrants it.
+	 */
+	if(align == sizeof(vlong))
+		align = sizeof(long);
+
+	/*
+	 * Check align is a power of 2, then addr alignment.
+	 */
+	if((align != 0 && !(align & (align-1))) && !(addr & (align-1)))
+		return;
+	postnote(up, 1, "sys: odd address", NDebug);
+	error(Ebadarg);
+	/*NOTREACHED*/
 }
 
 uintptr
--- /sys/src/9/vt5/fns.h	Thu May 29 00:00:00 2014
+++ /sys/src/9/vt5/fns.h	Thu May 29 00:00:00 2014
@@ -47,7 +47,6 @@
 void	dump(void *, int);
 void	eieio(void);
 void	etherclock(void);
-void	evenaddr(uintptr);
 void	fifoinit(Ether *);
 void	firmware(int);
 int	fpipower(Ureg*);
@@ -184,6 +183,7 @@
 void	uncinit(void);
 void	uncinitwait(void);
 #define	userureg(ur)	(((ur)->status & MSR_PR) != 0)
+void	validalign(uintptr, unsigned);
 void	verifyproc(Proc *);
 void	verifymach(Mach *);
 #define	waserror()	(up->nerrlab++, setlabel(&up->errlab[up->nerrlab-1]))