runtime: remove g.stackAlloc

Since we're no longer stealing space for the stack barrier array from
the stack allocation, the stack allocation is simply
g.stack.hi-g.stack.lo.

Updates #17503.

Change-Id: Id9b450ae12c3df9ec59cfc4365481a0a16b7c601
Reviewed-on: https://go-review.googlesource.com/36621
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

4 files changed, 13 insertions, 21 deletions

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index c960d81408..5fc7d25390 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -2812,7 +2812,6 @@ func malg(stacksize int32) *g {
 		})
 		newg.stackguard0 = newg.stack.lo + _StackGuard
 		newg.stackguard1 = ^uintptr(0)
-		newg.stackAlloc = uintptr(stacksize)
 	}
 	return newg
 }
@@ -2949,11 +2948,11 @@ func gfput(_p_ *p, gp *g) {
 		throw("gfput: bad status (not Gdead)")
 	}
 
-	stksize := gp.stackAlloc
+	stksize := gp.stack.hi - gp.stack.lo
 
 	if stksize != _FixedStack {
 		// non-standard stack size - free it.
-		stackfree(gp.stack, gp.stackAlloc)
+		stackfree(gp.stack)
 		gp.stack.lo = 0
 		gp.stack.hi = 0
 		gp.stackguard0 = 0
@@ -3016,13 +3015,12 @@ retry:
 				gp.stack = stackalloc(_FixedStack)
 			})
 			gp.stackguard0 = gp.stack.lo + _StackGuard
-			gp.stackAlloc = _FixedStack
 		} else {
 			if raceenabled {
-				racemalloc(unsafe.Pointer(gp.stack.lo), gp.stackAlloc)
+				racemalloc(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo)
 			}
 			if msanenabled {
-				msanmalloc(unsafe.Pointer(gp.stack.lo), gp.stackAlloc)
+				msanmalloc(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo)
 			}
 		}
 	}
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 4812268a19..f0b919453a 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -341,7 +341,6 @@ type g struct {
 	_panic         *_panic // innermost panic - offset known to liblink
 	_defer         *_defer // innermost defer
 	m              *m      // current m; offset known to arm liblink
-	stackAlloc     uintptr // stack allocation is [stack.lo,stack.lo+stackAlloc)
 	sched          gobuf
 	syscallsp      uintptr        // if status==Gsyscall, syscallsp = sched.sp to use during gc
 	syscallpc      uintptr        // if status==Gsyscall, syscallpc = sched.pc to use during gc
diff --git a/src/runtime/signal_unix.go b/src/runtime/signal_unix.go
index 9a33269367..e0ea724f97 100644
--- a/src/runtime/signal_unix.go
+++ b/src/runtime/signal_unix.go
@@ -712,7 +712,6 @@ type gsignalStack struct {
 	stack       stack
 	stackguard0 uintptr
 	stackguard1 uintptr
-	stackAlloc  uintptr
 	stktopsp    uintptr
 }
 
@@ -729,7 +728,6 @@ func setGsignalStack(st *stackt, old *gsignalStack) {
 		old.stack = g.m.gsignal.stack
 		old.stackguard0 = g.m.gsignal.stackguard0
 		old.stackguard1 = g.m.gsignal.stackguard1
-		old.stackAlloc = g.m.gsignal.stackAlloc
 		old.stktopsp = g.m.gsignal.stktopsp
 	}
 	stsp := uintptr(unsafe.Pointer(st.ss_sp))
@@ -737,7 +735,6 @@ func setGsignalStack(st *stackt, old *gsignalStack) {
 	g.m.gsignal.stack.hi = stsp + st.ss_size
 	g.m.gsignal.stackguard0 = stsp + _StackGuard
 	g.m.gsignal.stackguard1 = stsp + _StackGuard
-	g.m.gsignal.stackAlloc = st.ss_size
 }
 
 // restoreGsignalStack restores the gsignal stack to the value it had
@@ -749,7 +746,6 @@ func restoreGsignalStack(st *gsignalStack) {
 	gp.stack = st.stack
 	gp.stackguard0 = st.stackguard0
 	gp.stackguard1 = st.stackguard1
-	gp.stackAlloc = st.stackAlloc
 	gp.stktopsp = st.stktopsp
 }
 
diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index 1bd7e87b2e..d6a4e4ea80 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -415,9 +415,10 @@ func stackalloc(n uint32) stack {
 // resources and must not split the stack.
 //
 //go:systemstack
-func stackfree(stk stack, n uintptr) {
+func stackfree(stk stack) {
 	gp := getg()
 	v := unsafe.Pointer(stk.lo)
+	n := stk.hi - stk.lo
 	if n&(n-1) != 0 {
 		throw("stack not a power of 2")
 	}
@@ -852,7 +853,7 @@ func copystack(gp *g, newsize uintptr, sync bool) {
 		fillstack(new, 0xfd)
 	}
 	if stackDebug >= 1 {
-		print("copystack gp=", gp, " [", hex(old.lo), " ", hex(old.hi-used), " ", hex(old.hi), "]/", gp.stackAlloc, " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n")
+		print("copystack gp=", gp, " [", hex(old.lo), " ", hex(old.hi-used), " ", hex(old.hi), "]", " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n")
 	}
 
 	// Compute adjustment.
@@ -895,8 +896,6 @@ func copystack(gp *g, newsize uintptr, sync bool) {
 	gp.stack = new
 	gp.stackguard0 = new.lo + _StackGuard // NOTE: might clobber a preempt request
 	gp.sched.sp = new.hi - used
-	oldsize := gp.stackAlloc
-	gp.stackAlloc = newsize
 	gp.stktopsp += adjinfo.delta
 
 	// Adjust pointers in the new stack.
@@ -906,7 +905,7 @@ func copystack(gp *g, newsize uintptr, sync bool) {
 	if stackPoisonCopy != 0 {
 		fillstack(old, 0xfc)
 	}
-	stackfree(old, oldsize)
+	stackfree(old)
 }
 
 // round x up to a power of 2.
@@ -1051,9 +1050,9 @@ func newstack(ctxt unsafe.Pointer) {
 	}
 
 	// Allocate a bigger segment and move the stack.
-	oldsize := int(gp.stackAlloc)
+	oldsize := gp.stack.hi - gp.stack.lo
 	newsize := oldsize * 2
-	if uintptr(newsize) > maxstacksize {
+	if newsize > maxstacksize {
 		print("runtime: goroutine stack exceeds ", maxstacksize, "-byte limit\n")
 		throw("stack overflow")
 	}
@@ -1064,7 +1063,7 @@ func newstack(ctxt unsafe.Pointer) {
 
 	// The concurrent GC will not scan the stack while we are doing the copy since
 	// the gp is in a Gcopystack status.
-	copystack(gp, uintptr(newsize), true)
+	copystack(gp, newsize, true)
 	if stackDebug >= 1 {
 		print("stack grow done\n")
 	}
@@ -1098,7 +1097,7 @@ func shrinkstack(gp *g) {
 		if gp.stack.lo != 0 {
 			// Free whole stack - it will get reallocated
 			// if G is used again.
-			stackfree(gp.stack, gp.stackAlloc)
+			stackfree(gp.stack)
 			gp.stack.lo = 0
 			gp.stack.hi = 0
 		}
@@ -1120,7 +1119,7 @@ func shrinkstack(gp *g) {
 		return
 	}
 
-	oldsize := gp.stackAlloc
+	oldsize := gp.stack.hi - gp.stack.lo
 	newsize := oldsize / 2
 	// Don't shrink the allocation below the minimum-sized stack
 	// allocation.