terminal: add ability to show disassembly instead of source (#3047)

Adds ability to show current position as disassembly instead of source
listing every time execution stops. Change default to show disassembly
after step-instruction and source listing in every other case.

Fixes #2878

pkg/config/config.go

@@ -9,6 +9,7 @@ import (
 	"path"
 	"runtime"
 
+	"github.com/go-delve/delve/service/api"
 	"gopkg.in/yaml.v2"
 )
 
@@ -16,6 +17,10 @@ const (
 	configDir       string = "dlv"
 	configDirHidden string = ".dlv"
 	configFile      string = "config.yml"
+
+	PositionSource      = "source"
+	PositionDisassembly = "disassembly"
+	PositionDefault     = "default"
 )
 
 // SubstitutePathRule describes a rule for substitution of path to source code file.
@@ -76,9 +81,19 @@ type Config struct {
 	// called (i.e. when execution stops, listCommand is used, etc)
 	SourceListLineCount *int `yaml:"source-list-line-count,omitempty"`
 
-	// DebugFileDirectories is the list of directories Delve will use
+	// DebugInfoDirectories is the list of directories Delve will use
 	// in order to resolve external debug info files.
 	DebugInfoDirectories []string `yaml:"debug-info-directories"`
+
+	// Position controls how the current position in the program is displayed.
+	// There are three possible values:
+	//  - source: always show the current position in the program's source
+	//    code.
+	//  - disassembly: always should the current position by disassembling the
+	//    current function.
+	//  - default (or the empty string): use disassembly for step-instruction,
+	//    source for everything else.
+	Position string `yaml:"position"`
 }
 
 func (c *Config) GetSourceListLineCount() int {
@@ -90,6 +105,20 @@ func (c *Config) GetSourceListLineCount() int {
 	return n
 }
 
+func (c *Config) GetDisassembleFlavour() api.AssemblyFlavour {
+	if c == nil || c.DisassembleFlavor == nil {
+		return api.IntelFlavour
+	}
+	switch *c.DisassembleFlavor {
+	case "go":
+		return api.GoFlavour
+	case "gnu":
+		return api.GNUFlavour
+	default:
+		return api.IntelFlavour
+	}
+}
+
 // LoadConfig attempts to populate a Config object from the config.yml file.
 func LoadConfig() (*Config, error) {
 	err := createConfigPath()

pkg/terminal/command.go

@@ -1175,7 +1175,7 @@ func restartRecorded(t *Term, ctx callContext, args string) error {
 		return err
 	}
 	printcontext(t, state)
-	printfile(t, state.CurrentThread.File, state.CurrentThread.Line, true)
+	printPos(t, state.CurrentThread, printPosShowArrow)
 	t.onStop()
 	return nil
 }
@@ -1328,7 +1328,7 @@ func (c *Commands) cont(t *Term, ctx callContext, args string) error {
 		}
 		printcontext(t, state)
 	}
-	printfile(t, state.CurrentThread.File, state.CurrentThread.Line, true)
+	printPos(t, state.CurrentThread, printPosShowArrow)
 	return nil
 }
 
@@ -1336,7 +1336,7 @@ func continueUntilCompleteNext(t *Term, state *api.DebuggerState, op string, sho
 	defer t.onStop()
 	if !state.NextInProgress {
 		if shouldPrintFile {
-			printfile(t, state.CurrentThread.File, state.CurrentThread.Line, true)
+			printPos(t, state.CurrentThread, printPosShowArrow)
 		}
 		return nil
 	}
@@ -1356,7 +1356,7 @@ func continueUntilCompleteNext(t *Term, state *api.DebuggerState, op string, sho
 				fallthrough
 			default:
 				t.client.CancelNext()
-				printfile(t, state.CurrentThread.File, state.CurrentThread.Line, true)
+				printPos(t, state.CurrentThread, printPosShowArrow)
 				return err
 			}
 		} else {
@@ -1372,7 +1372,7 @@ func continueUntilCompleteNext(t *Term, state *api.DebuggerState, op string, sho
 			printcontext(t, state)
 		}
 		if !state.NextInProgress {
-			printfile(t, state.CurrentThread.File, state.CurrentThread.Line, true)
+			printPos(t, state.CurrentThread, printPosShowArrow)
 			return nil
 		}
 	}
@@ -1452,7 +1452,7 @@ func (c *Commands) stepInstruction(t *Term, ctx callContext, args string) error
 		return err
 	}
 	printcontext(t, state)
-	printfile(t, state.CurrentThread.File, state.CurrentThread.Line, true)
+	printPos(t, state.CurrentThread, printPosShowArrow|printPosStepInstruction)
 	return nil
 }
 
@@ -2385,17 +2385,7 @@ func disassCommand(t *Term, ctx callContext, args string) error {
 		rest = argv[1]
 	}
 
-	flavor := api.IntelFlavour
-	if t.conf != nil && t.conf.DisassembleFlavor != nil {
-		switch *t.conf.DisassembleFlavor {
-		case "go":
-			flavor = api.GoFlavour
-		case "gnu":
-			flavor = api.GNUFlavour
-		default:
-			flavor = api.IntelFlavour
-		}
-	}
+	flavor := t.conf.GetDisassembleFlavour()
 
 	var disasm api.AsmInstructions
 	var disasmErr error
@@ -2438,7 +2428,7 @@ func disassCommand(t *Term, ctx callContext, args string) error {
 		return disasmErr
 	}
 
-	disasmPrint(disasm, t.stdout)
+	disasmPrint(disasm, t.stdout, true)
 
 	return nil
 }
@@ -2678,6 +2668,26 @@ func printTracepoint(t *Term, th *api.Thread, bpname string, fn *api.Function, a
 	}
 }
 
+type printPosFlags uint8
+
+const (
+	printPosShowArrow printPosFlags = 1 << iota
+	printPosStepInstruction
+)
+
+func printPos(t *Term, th *api.Thread, flags printPosFlags) error {
+	if flags&printPosStepInstruction != 0 {
+		if t.conf.Position == config.PositionSource {
+			return printfile(t, th.File, th.Line, flags&printPosShowArrow != 0)
+		}
+		return printdisass(t, th.PC)
+	}
+	if t.conf.Position == config.PositionDisassembly {
+		return printdisass(t, th.PC)
+	}
+	return printfile(t, th.File, th.Line, flags&printPosShowArrow != 0)
+}
+
 func printfile(t *Term, filename string, line int, showArrow bool) error {
 	if filename == "" {
 		return nil
@@ -2712,6 +2722,35 @@ func printfile(t *Term, filename string, line int, showArrow bool) error {
 	return t.stdout.ColorizePrint(file.Name(), file, line-lineCount, line+lineCount+1, arrowLine)
 }
 
+func printdisass(t *Term, pc uint64) error {
+	disasm, err := t.client.DisassemblePC(api.EvalScope{GoroutineID: -1, Frame: 0, DeferredCall: 0}, pc, t.conf.GetDisassembleFlavour())
+	if err != nil {
+		return err
+	}
+
+	lineCount := t.conf.GetSourceListLineCount()
+
+	showHeader := true
+	for i := range disasm {
+		if disasm[i].AtPC {
+			s := i - lineCount
+			if s < 0 {
+				s = 0
+			}
+			e := i + lineCount + 1
+			if e > len(disasm) {
+				e = len(disasm)
+			}
+			showHeader = s == 0
+			disasm = disasm[s:e]
+			break
+		}
+	}
+
+	disasmPrint(disasm, t.stdout, showHeader)
+	return nil
+}
+
 // ExitRequestError is returned when the user
 // exits Delve.
 type ExitRequestError struct{}
@@ -2908,7 +2947,7 @@ func (c *Commands) rewind(t *Term, ctx callContext, args string) error {
 		}
 		printcontext(t, state)
 	}
-	printfile(t, state.CurrentThread.File, state.CurrentThread.Line, true)
+	printPos(t, state.CurrentThread, printPosShowArrow)
 	return nil
 }
 

pkg/terminal/command_test.go

@@ -1331,3 +1331,14 @@ func TestTranscript(t *testing.T) {
 		os.Remove(name)
 	})
 }
+
+func TestDisassPosCmd(t *testing.T) {
+	withTestTerminal("testvariables2", t, func(term *FakeTerminal) {
+		term.MustExec("continue")
+		out := term.MustExec("step-instruction")
+		t.Logf("%q\n", out)
+		if !strings.Contains(out, "call $runtime.Breakpoint") && !strings.Contains(out, "CALL runtime.Breakpoint(SB)") {
+			t.Errorf("output doesn't look like disassembly")
+		}
+	})
+}

pkg/terminal/disasmprint.go

@@ -10,10 +10,10 @@ import (
 	"github.com/go-delve/delve/service/api"
 )
 
-func disasmPrint(dv api.AsmInstructions, out io.Writer) {
+func disasmPrint(dv api.AsmInstructions, out io.Writer, showHeader bool) {
 	bw := bufio.NewWriter(out)
 	defer bw.Flush()
-	if len(dv) > 0 && dv[0].Loc.Function != nil {
+	if len(dv) > 0 && dv[0].Loc.Function != nil && showHeader {
 		fmt.Fprintf(bw, "TEXT %s(SB) %s\n", dv[0].Loc.Function.Name(), dv[0].Loc.File)
 	}
 	tw := tabwriter.NewWriter(bw, 1, 8, 1, '\t', 0)