proc/native: disable Go 1.14 async preemption on Windows

See golang/go#36494

pkg/proc/core/core.go

@@ -223,7 +223,7 @@ func OpenCore(corePath, exePath string, debugInfoDirs []string) (*Process, error
 // initialize for core files doesn't do much
 // aside from call the post initialization setup.
 func (p *Process) initialize(path string, debugInfoDirs []string) error {
-	return proc.PostInitializationSetup(p, path, debugInfoDirs, p.writeBreakpoint)
+	return proc.PostInitializationSetup(p, path, debugInfoDirs, p.writeBreakpoint, false)
 }
 
 // BinInfo will return the binary info.

pkg/proc/gdbserial/gdbserver.go

@@ -529,7 +529,7 @@ func (p *Process) initialize(path string, debugInfoDirs []string) error {
 			return err
 		}
 	}
-	if err = proc.PostInitializationSetup(p, path, debugInfoDirs, p.writeBreakpoint); err != nil {
+	if err = proc.PostInitializationSetup(p, path, debugInfoDirs, p.writeBreakpoint, false); err != nil {
 		p.conn.conn.Close()
 		return err
 	}

pkg/proc/interface.go

@@ -117,8 +117,9 @@ type CommonProcess struct {
 	goroutineCache
 
 	fncallEnabled bool
+	fncallForG    map[int]*callInjection
 
-	fncallForG map[int]*callInjection
+	asyncPreemptOff int64 // cached value of runtime/debug.asyncpreemptoff
 }
 
 type goroutineCache struct {

pkg/proc/native/proc.go

@@ -360,7 +360,7 @@ func (dbp *Process) initialize(path string, debugInfoDirs []string) error {
 	if err := dbp.updateThreadList(); err != nil {
 		return err
 	}
-	return proc.PostInitializationSetup(dbp, path, debugInfoDirs, dbp.writeBreakpoint)
+	return proc.PostInitializationSetup(dbp, path, debugInfoDirs, dbp.writeBreakpoint, runtime.GOOS == "windows")
 }
 
 // SetSelectedGoroutine will set internally the goroutine that should be

pkg/proc/native/proc_windows.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 	"syscall"
 	"unsafe"
 
@@ -55,6 +56,15 @@ func Launch(cmd []string, wd string, foreground bool, _ []string) (*Process, err
 	}
 	closer.Close()
 
+	env := os.Environ()
+	for i := range env {
+		if strings.HasPrefix(env[i], "GODEBUG=") {
+			// Go 1.14 asynchronous preemption mechanism is incompatible with
+			// debuggers, see: https://github.com/golang/go/issues/36494
+			env[i] += ",asyncpreemptoff=1"
+		}
+	}
+
 	var p *os.Process
 	dbp := New(0)
 	dbp.common = proc.NewCommonProcess(true)
@@ -65,6 +75,7 @@ func Launch(cmd []string, wd string, foreground bool, _ []string) (*Process, err
 			Sys: &syscall.SysProcAttr{
 				CreationFlags: _DEBUG_ONLY_THIS_PROCESS,
 			},
+			Env: env,
 		}
 		p, err = os.StartProcess(argv0Go, cmd, attr)
 	})
@@ -473,6 +484,9 @@ func (dbp *Process) stop(trapthread *Thread) (err error) {
 
 func (dbp *Process) detach(kill bool) error {
 	if !kill {
+		//TODO(aarzilli): when debug.Target exist Detach should be moved to
+		// debug.Target and the call to RestoreAsyncPreempt should be moved there.
+		proc.RestoreAsyncPreempt(dbp)
 		for _, thread := range dbp.threads {
 			_, err := _ResumeThread(thread.os.hThread)
 			if err != nil {

pkg/proc/proc.go

@@ -5,9 +5,12 @@ import (
 	"errors"
 	"fmt"
 	"go/ast"
+	"go/constant"
 	"go/token"
 	"path/filepath"
 	"strconv"
+
+	"github.com/go-delve/delve/pkg/goversion"
 )
 
 // ErrNotExecutable is returned after attempting to execute a non-executable file
@@ -52,7 +55,7 @@ func (pe ProcessDetachedError) Error() string {
 
 // PostInitializationSetup handles all of the initialization procedures
 // that must happen after Delve creates or attaches to a process.
-func PostInitializationSetup(p Process, path string, debugInfoDirs []string, writeBreakpoint WriteBreakpointFn) error {
+func PostInitializationSetup(p Process, path string, debugInfoDirs []string, writeBreakpoint WriteBreakpointFn, disableAsyncPreempt bool) error {
 	entryPoint, err := p.EntryPoint()
 	if err != nil {
 		return err
@@ -76,6 +79,10 @@ func PostInitializationSetup(p Process, path string, debugInfoDirs []string, wri
 
 	p.Common().goroutineCache.init(p.BinInfo())
 
+	if disableAsyncPreempt {
+		setAsyncPreemptOff(p, 1)
+	}
+
 	return nil
 }
 
@@ -819,3 +826,34 @@ func FirstPCAfterPrologue(p Process, fn *Function, sameline bool) (uint64, error
 
 	return pc, nil
 }
+
+func setAsyncPreemptOff(p Process, v int64) {
+	logger := p.BinInfo().logger
+	if producer := p.BinInfo().Producer(); producer == "" || !goversion.ProducerAfterOrEqual(producer, 1, 14) {
+		return
+	}
+	scope := globalScope(p.BinInfo(), p.BinInfo().Images[0], p.CurrentThread())
+	debugv, err := scope.findGlobal("runtime", "debug")
+	if err != nil || debugv.Unreadable != nil {
+		logger.Warnf("could not find runtime/debug variable (or unreadable): %v %v", err, debugv.Unreadable)
+		return
+	}
+	asyncpreemptoffv, err := debugv.structMember("asyncpreemptoff")
+	if err != nil {
+		logger.Warnf("could not find asyncpreemptoff field: %v", err)
+		return
+	}
+	asyncpreemptoffv.loadValue(loadFullValue)
+	if asyncpreemptoffv.Unreadable != nil {
+		logger.Warnf("asyncpreemptoff field unreadable: %v", asyncpreemptoffv.Unreadable)
+		return
+	}
+	p.Common().asyncPreemptOff, _ = constant.Int64Val(asyncpreemptoffv.Value)
+
+	err = scope.setValue(asyncpreemptoffv, newConstant(constant.MakeInt64(v), scope.Mem), "")
+	logger.Warnf("could not set asyncpreemptoff %v", err)
+}
+
+func RestoreAsyncPreempt(p Process) {
+	setAsyncPreemptOff(p, p.Common().asyncPreemptOff)
+}