terminal,service: Add support for rev prefix and step-instruction (#1596)

Support for rev {next,step} is not currently implemented.

Documentation/cli/README.md

@@ -32,6 +32,7 @@ Command | Description
 [print](#print) | Evaluate an expression.
 [regs](#regs) | Print contents of CPU registers.
 [restart](#restart) | Restart process from a checkpoint or event.
+[rev](#rev) | Reverses the execution of the target program for the command specified.
 [rewind](#rewind) | Run backwards until breakpoint or program termination.
 [set](#set) | Changes the value of a variable.
 [source](#source) | Executes a file containing a list of delve commands
@@ -329,6 +330,11 @@ Restart process from a checkpoint or event.
 
 Aliases: r
 
+## rev
+Reverses the execution of the target program for the command specified.
+Currently, only the rev step-instruction command is supported.
+
+
 ## rewind
 Run backwards until breakpoint or program termination.
 

pkg/terminal/command.go

@@ -34,6 +34,7 @@ const (
 	noPrefix = cmdPrefix(0)
 	onPrefix = cmdPrefix(1 << iota)
 	deferredPrefix
+	revPrefix
 )
 
 type callContext struct {
@@ -136,7 +137,7 @@ the arguments.  With -noargs, the process starts with an empty commandline.
 `},
 		{aliases: []string{"continue", "c"}, cmdFn: c.cont, helpMsg: "Run until breakpoint or program termination."},
 		{aliases: []string{"step", "s"}, cmdFn: c.step, helpMsg: "Single step through program."},
-		{aliases: []string{"step-instruction", "si"}, cmdFn: c.stepInstruction, helpMsg: "Single step a single cpu instruction."},
+		{aliases: []string{"step-instruction", "si"}, allowedPrefixes: revPrefix, cmdFn: c.stepInstruction, helpMsg: "Single step a single cpu instruction."},
 		{aliases: []string{"next", "n"}, cmdFn: c.next, helpMsg: "Step over to next source line."},
 		{aliases: []string{"stepout"}, cmdFn: c.stepout, helpMsg: "Step out of the current function."},
 		{aliases: []string{"call"}, cmdFn: c.call, helpMsg: `Resumes process, injecting a function call (EXPERIMENTAL!!!)
@@ -379,6 +380,12 @@ The "note" is arbitrary text that can be used to identify the checkpoint, if it
 			helpMsg: `Deletes checkpoint.
 
 	clear-checkpoint <id>`,
+		})
+		c.cmds = append(c.cmds, command{
+			aliases: []string{"rev"},
+			cmdFn:   c.revCmd,
+			helpMsg: `Reverses the execution of the target program for the command specified.
+Currently, only the rev step-instruction command is supported.`,
 		})
 		for i := range c.cmds {
 			v := &c.cmds[i]
@@ -988,7 +995,15 @@ func (c *Commands) stepInstruction(t *Term, ctx callContext, args string) error
 	if c.frame != 0 {
 		return notOnFrameZeroErr
 	}
-	state, err := exitedToError(t.client.StepInstruction())
+
+	var fn func() (*api.DebuggerState, error)
+	if ctx.Prefix == revPrefix {
+		fn = t.client.ReverseStepInstruction
+	} else {
+		fn = t.client.StepInstruction
+	}
+
+	state, err := exitedToError(fn())
 	if err != nil {
 		printcontextNoState(t)
 		return err
@@ -998,6 +1013,18 @@ func (c *Commands) stepInstruction(t *Term, ctx callContext, args string) error
 	return nil
 }
 
+func (c *Commands) revCmd(t *Term, ctx callContext, args string) error {
+	if len(args) == 0 {
+		return errors.New("not enough arguments")
+	}
+
+	ctx.Prefix = revPrefix
+	if err := c.CallWithContext(args, t, ctx); err != nil {
+		return err
+	}
+	return nil
+}
+
 func (c *Commands) next(t *Term, ctx callContext, args string) error {
 	if err := scopePrefixSwitch(t, ctx); err != nil {
 		return err

service/api/types.go

@@ -356,6 +356,8 @@ const (
 	StepOut = "stepOut"
 	// StepInstruction continues for exactly 1 cpu instruction.
 	StepInstruction = "stepInstruction"
+	// ReverseStepInstruction reverses execution for exactly 1 cpu instruction.
+	ReverseStepInstruction = "reverseStepInstruction"
 	// Next continues to the next source line, not entering function calls.
 	Next = "next"
 	// SwitchThread switches the debugger's current thread context.

service/client.go

@@ -43,6 +43,8 @@ type Client interface {
 
 	// SingleStep will step a single cpu instruction.
 	StepInstruction() (*api.DebuggerState, error)
+	// ReverseSingleStep will reverse step a single cpu instruction.
+	ReverseStepInstruction() (*api.DebuggerState, error)
 	// SwitchThread switches the current thread context.
 	SwitchThread(threadID int) (*api.DebuggerState, error)
 	// SwitchGoroutine switches the current goroutine (and the current thread as well)

service/debugger/debugger.go

@@ -624,6 +624,15 @@ func (d *Debugger) Command(command *api.DebuggerCommand) (*api.DebuggerState, er
 	case api.StepInstruction:
 		d.log.Debug("single stepping")
 		err = d.target.StepInstruction()
+	case api.ReverseStepInstruction:
+		d.log.Debug("reverse single stepping")
+		if err := d.target.Direction(proc.Backward); err != nil {
+			return nil, err
+		}
+		defer func() {
+			d.target.Direction(proc.Forward)
+		}()
+		err = d.target.StepInstruction()
 	case api.StepOut:
 		d.log.Debug("step out")
 		err = proc.StepOut(d.target)

service/rpc1/client.go

@@ -125,6 +125,12 @@ func (c *RPCClient) StepInstruction() (*api.DebuggerState, error) {
 	return state, err
 }
 
+func (c *RPCClient) ReverseStepInstruction() (*api.DebuggerState, error) {
+	state := new(api.DebuggerState)
+	err := c.call("Command", &api.DebuggerCommand{Name: api.ReverseStepInstruction}, state)
+	return state, err
+}
+
 func (c *RPCClient) SwitchThread(threadID int) (*api.DebuggerState, error) {
 	state := new(api.DebuggerState)
 	cmd := &api.DebuggerCommand{

service/rpc2/client.go

@@ -160,6 +160,12 @@ func (c *RPCClient) StepInstruction() (*api.DebuggerState, error) {
 	return &out.State, err
 }
 
+func (c *RPCClient) ReverseStepInstruction() (*api.DebuggerState, error) {
+	var out CommandOut
+	err := c.call("Command", api.DebuggerCommand{Name: api.ReverseStepInstruction}, &out)
+	return &out.State, err
+}
+
 func (c *RPCClient) SwitchThread(threadID int) (*api.DebuggerState, error) {
 	var out CommandOut
 	cmd := api.DebuggerCommand{