runtime: mark TestTracebackArgs test functions nosplit

The argument liveness tests expect outputs where a dead stack slot
has a poisoned value. If the test function is preempted at the
prologue, it will go with the morestack code path which will spill
all the argument registers. Mark them nosplit to avoid that.

Should fix #49354.

Change-Id: I3b13e72e925748687a53c494bfaa70f07d9496fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/361211
Trust: Cherry Mui <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Austin Clements <[email protected]>

Author: cherrymui

src/runtime/traceback_test.go

@@ -353,6 +353,9 @@ func testTracebackArgs8d(a testArgsType8d) int {
 	return n
 }
 
+// nosplit to avoid preemption or morestack spilling registers.
+//
+//go:nosplit
 //go:noinline
 func testTracebackArgs9(a int64, b int32, c int16, d int8, x [2]int, y int) int {
 	if a < 0 {
@@ -366,15 +369,20 @@ func testTracebackArgs9(a int64, b int32, c int16, d int8, x [2]int, y int) int
 	return n
 }
 
+// nosplit to avoid preemption or morestack spilling registers.
+//
+//go:nosplit
 //go:noinline
 func testTracebackArgs10(a, b, c, d, e int32) int {
 	// no use of any args
 	return runtime.Stack(testTracebackArgsBuf[:], false)
 }
 
 // norace to avoid race instrumentation changing spill locations.
+// nosplit to avoid preemption or morestack spilling registers.
 //
 //go:norace
+//go:nosplit
 //go:noinline
 func testTracebackArgs11a(a, b, c int32) int {
 	if a < 0 {
@@ -387,8 +395,10 @@ func testTracebackArgs11a(a, b, c int32) int {
 }
 
 // norace to avoid race instrumentation changing spill locations.
+// nosplit to avoid preemption or morestack spilling registers.
 //
 //go:norace
+//go:nosplit
 //go:noinline
 func testTracebackArgs11b(a, b, c, d int32) int {
 	var x int32