svn commit: r221894 - head/sys/ia64/ia64

[Marcel Moolenaar]

Author: marcel
Date: Sat May 14 14:55:15 2011
New Revision: 221894
URL: http://svn.freebsd.org/changeset/base/221894

Log:
  Prefer switching the memory stack from user to kernel *before* switching
  the register stack. While the ordering doesn't matter, it creates an
  invariant not previously there: the memory stack pointer will always be
  larger than the register stack pointer. With this invariant in place,
  it's easier to add instrumentation code that detects a stack overflow
  because in such a scenario the memory stack pointer and register stack
  pointers have crossed each other.
  
  Aside: basic kernel operation needs about half the stack size (~16K)
  at most. We have plenty of head room on the kernel stack...

Modified:
  head/sys/ia64/ia64/syscall.S

Modified: head/sys/ia64/ia64/syscall.S
==============================================================================
--- head/sys/ia64/ia64/syscall.S	Sat May 14 14:47:19 2011	(r221893)
+++ head/sys/ia64/ia64/syscall.S	Sat May 14 14:55:15 2011	(r221894)
@@ -239,21 +239,22 @@ ENTRY_NOPROFILE(epc_syscall, 8)
 	;;
 }
 {	.mmi
-	mov		ar.bspstore=r15
+	mov		r13=ar.k4
 	add		r30=-SIZEOF_TRAPFRAME,r14
 	mov		r20=sp
 	;;
 }
 {	.mii
-	mov		r13=ar.k4
+	mov		r21=ar.unat
 	dep		r30=0,r30,0,10
 	;;
 	add		sp=-16,r30
 	;;
 }
 {	.mmi
+	mov		ar.bspstore=r15
+	;;
 	mov		ar.rnat=r19
-	mov		r21=ar.unat
 	add		r31=8,r30
 	;;
 }