runtime, runtime/debug: access unexported runtime functions with //go:linkname, not assembly stubs

Change-Id: I88f80f5914d6e4c179f3d28aa59fc29b7ef0cc66
Reviewed-on: https://go-review.googlesource.com/15960Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/debug/stubs.go

@@ -8,12 +8,10 @@ import (
 	"time"
 )
 
-// Uses assembly to call corresponding runtime-internal functions.
+// Implemented in package runtime.
+func readGCStats(*[]time.Duration)
+func freeOSMemory()
 func setMaxStack(int) int
 func setGCPercent(int32) int32
 func setPanicOnFault(bool) bool
 func setMaxThreads(int) int
-
-// Implemented in package runtime.
-func readGCStats(*[]time.Duration)
-func freeOSMemory()

src/runtime/debug/stubs.s

-// Copyright 2014 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include "textflag.h"
-
-#ifdef GOARCH_arm
-#define JMP B
-#endif
-#ifdef GOARCH_arm64
-#define JMP B
-#endif
-#ifdef GOARCH_ppc64
-#define JMP BR
-#endif
-#ifdef GOARCH_ppc64le
-#define JMP BR
-#endif
-
-TEXT ·setMaxStack(SB),NOSPLIT,$0-0
-  JMP runtime·setMaxStack(SB)
-
-TEXT ·setGCPercent(SB),NOSPLIT,$0-0
-  JMP runtime·setGCPercent(SB)
-
-TEXT ·setPanicOnFault(SB),NOSPLIT,$0-0
-  JMP runtime·setPanicOnFault(SB)
-
-TEXT ·setMaxThreads(SB),NOSPLIT,$0-0
-  JMP runtime·setMaxThreads(SB)

src/runtime/mgc.go

@@ -196,6 +196,7 @@ func gcenable() {
 	memstats.enablegc = true // now that runtime is initialized, GC is okay
 }
 
+//go:linkname setGCPercent runtime/debug.setGCPercent
 func setGCPercent(in int32) (out int32) {
 	lock(&mheap_.lock)
 	out = gcpercent

src/runtime/proc1.go

@@ -3645,6 +3645,7 @@ func testSchedLocalQueueSteal() {
 	}
 }
 
+//go:linkname setMaxThreads runtime/debug.setMaxThreads
 func setMaxThreads(in int) (out int) {
 	lock(&sched.lock)
 	out = int(sched.maxmcount)

src/runtime/rdebug.go

@@ -4,12 +4,16 @@
 
 package runtime
 
+import _ "unsafe" // for go:linkname
+
+//go:linkname setMaxStack runtime/debug.setMaxStack
 func setMaxStack(in int) (out int) {
 	out = int(maxstacksize)
 	maxstacksize = uintptr(in)
 	return out
 }
 
+//go:linkname setPanicOnFault runtime/debug.setPanicOnFault
 func setPanicOnFault(new bool) (old bool) {
 	mp := acquirem()
 	old = mp.curg.paniconfault