proc/native, proc/gdbserial: StepInstruction without goroutine

proc.Process.StepInstruction should work even if there is no goroutine
selected.

pkg/proc/gdbserial/gdbserver.go

@@ -623,25 +623,26 @@ continueLoop:
 }
 
 func (p *Process) StepInstruction() error {
-	if p.selectedGoroutine == nil {
-		return errors.New("cannot single step: no selected goroutine")
-	}
-	if p.selectedGoroutine.Thread == nil {
-		if _, err := p.SetBreakpoint(p.selectedGoroutine.PC, proc.NextBreakpoint, proc.SameGoroutineCondition(p.selectedGoroutine)); err != nil {
-			return err
+	thread := p.currentThread
+	if p.selectedGoroutine != nil {
+		if p.selectedGoroutine.Thread == nil {
+			if _, err := p.SetBreakpoint(p.selectedGoroutine.PC, proc.NextBreakpoint, proc.SameGoroutineCondition(p.selectedGoroutine)); err != nil {
+				return err
+			}
+			return proc.Continue(p)
 		}
-		return proc.Continue(p)
+		thread = p.selectedGoroutine.Thread.(*Thread)
 	}
 	p.allGCache = nil
 	if p.exited {
 		return &proc.ProcessExitedError{Pid: p.conn.pid}
 	}
-	p.selectedGoroutine.Thread.(*Thread).clearBreakpointState()
-	err := p.selectedGoroutine.Thread.(*Thread).StepInstruction()
+	thread.clearBreakpointState()
+	err := thread.StepInstruction()
 	if err != nil {
 		return err
 	}
-	return p.selectedGoroutine.Thread.(*Thread).SetCurrentBreakpoint()
+	return thread.SetCurrentBreakpoint()
 }
 
 func (p *Process) SwitchThread(tid int) error {

pkg/proc/native/proc.go

@@ -1,7 +1,6 @@
 package native
 
 import (
-	"errors"
 	"fmt"
 	"go/ast"
 	"os"
@@ -297,26 +296,27 @@ func (dbp *Process) ContinueOnce() (proc.Thread, error) {
 // asssociated with the selected goroutine. All other
 // threads will remain stopped.
 func (dbp *Process) StepInstruction() (err error) {
-	if dbp.selectedGoroutine == nil {
-		return errors.New("cannot single step: no selected goroutine")
-	}
-	if dbp.selectedGoroutine.Thread == nil {
-		// Step called on parked goroutine
-		if _, err := dbp.SetBreakpoint(dbp.selectedGoroutine.PC, proc.NextBreakpoint, proc.SameGoroutineCondition(dbp.selectedGoroutine)); err != nil {
-			return err
+	thread := dbp.currentThread
+	if dbp.selectedGoroutine != nil {
+		if dbp.selectedGoroutine.Thread == nil {
+			// Step called on parked goroutine
+			if _, err := dbp.SetBreakpoint(dbp.selectedGoroutine.PC, proc.NextBreakpoint, proc.SameGoroutineCondition(dbp.selectedGoroutine)); err != nil {
+				return err
+			}
+			return proc.Continue(dbp)
 		}
-		return proc.Continue(dbp)
+		thread = dbp.selectedGoroutine.Thread.(*Thread)
 	}
 	dbp.allGCache = nil
 	if dbp.exited {
 		return &proc.ProcessExitedError{}
 	}
-	dbp.selectedGoroutine.Thread.(*Thread).clearBreakpointState()
-	err = dbp.selectedGoroutine.Thread.(*Thread).StepInstruction()
+	thread.clearBreakpointState()
+	err = thread.StepInstruction()
 	if err != nil {
 		return err
 	}
-	return dbp.selectedGoroutine.Thread.(*Thread).SetCurrentBreakpoint()
+	return thread.SetCurrentBreakpoint()
 }
 
 // SwitchThread changes from current thread to the thread specified by `tid`.

pkg/proc/proc_test.go

@@ -19,6 +19,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/derekparker/delve/pkg/dwarf/frame"
 	"github.com/derekparker/delve/pkg/proc"
 	"github.com/derekparker/delve/pkg/proc/gdbserial"
 	"github.com/derekparker/delve/pkg/proc/native"
@@ -2954,3 +2955,29 @@ func TestIssue877(t *testing.T) {
 		}
 	})
 }
+
+func TestIssue893(t *testing.T) {
+	// Test what happens when next is called immediately after launching the
+	// executable, acceptable behaviors are: (a) no error, (b) no source at PC
+	// error.
+	protest.AllowRecording(t)
+	withTestProcess("increment", t, func(p proc.Process, fixture protest.Fixture) {
+		err := proc.Next(p)
+		if err == nil {
+			return
+		}
+		if _, ok := err.(*frame.NoFDEForPCError); ok {
+			return
+		}
+		assertNoError(err, t, "Next")
+	})
+}
+
+func TestStepInstructionNoGoroutine(t *testing.T) {
+	protest.AllowRecording(t)
+	withTestProcess("increment", t, func(p proc.Process, fixture protest.Fixture) {
+		// Call StepInstruction immediately after launching the program, it should
+		// work even though no goroutine is selected.
+		assertNoError(p.StepInstruction(), t, "StepInstruction")
+	})
+}