Revert "runtime: set stackguard1 on extra M g0"

This reverts CL 527056.

CL 525455 breaks darwin, alpine, and android. This CL must be reverted
in order to revert that CL.

For #62440.

Change-Id: I4e1b16e384b475a605e0214ca36c918d50faa22c
Reviewed-on: https://go-review.googlesource.com/c/go/+/527316
Reviewed-by: Cherry Mui <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: prattmic

src/runtime/cgocall.go

@@ -233,7 +233,6 @@ func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) {
 		g0.stack.hi = sp + 1024
 		g0.stack.lo = sp - 32*1024
 		g0.stackguard0 = g0.stack.lo + stackGuard
-		g0.stackguard1 = g0.stackguard0
 
 		print("M ", mp.id, " procid ", mp.procid, " runtime: cgocallback with sp=", hex(sp), " out of bounds [", hex(lo), ", ", hex(hi), "]")
 		print("\n")
@@ -272,7 +271,6 @@ func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) {
 		}
 	}
 	g0.stackguard0 = g0.stack.lo + stackGuard
-	g0.stackguard1 = g0.stackguard0
 }
 
 // Call from C back to Go. fn must point to an ABIInternal Go entry-point.

src/runtime/runtime2.go

@@ -423,7 +423,7 @@ type g struct {
 	// stack describes the actual stack memory: [stack.lo, stack.hi).
 	// stackguard0 is the stack pointer compared in the Go stack growth prologue.
 	// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
-	// stackguard1 is the stack pointer compared in the //go:systemstack stack growth prologue.
+	// stackguard1 is the stack pointer compared in the C stack growth prologue.
 	// It is stack.lo+StackGuard on g0 and gsignal stacks.
 	// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
 	stack       stack   // offset known to runtime/cgo