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...

1 files changed, 4 insertions, 3 deletions

diff --git a/sys/ia64/ia64/syscall.S b/sys/ia64/ia64/syscall.S
index b35523a..ef559e8 100644
--- a/sys/ia64/ia64/syscall.S
+++ b/sys/ia64/ia64/syscall.S
@@ -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
 	;;
 }