From c96d0a5ab262ab11d89d11f56c0c7857fbb57a2a Mon Sep 17 00:00:00 2001
From: Derek Parker <parkerderek86@gmail.com>
Date: Mon, 13 Jul 2015 16:34:51 -0500
Subject: [PATCH] Add pid flag to trace subcommand

---
 cmd/dlv/main.go | 36 +++++++++++++++++++++---------------
 proc/proc.go    |  5 +++++
 2 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/cmd/dlv/main.go b/cmd/dlv/main.go
index c282d5bc..0d9357e9 100644
--- a/cmd/dlv/main.go
+++ b/cmd/dlv/main.go
@@ -85,27 +85,31 @@ starts and attaches to it, and enables you to immediately begin debugging your p
 	rootCommand.AddCommand(runCommand)
 
 	// 'trace' subcommand.
+	var traceAttachPid int
 	traceCommand := &cobra.Command{
-		Use:   "trace [regexp]",
+		Use:   "trace [regexp] [flags]",
 		Short: "Compile and begin tracing program.",
 		Long:  "Trace program execution. Will set a tracepoint on every function matching [regexp] and output information when tracepoint is hit.",
 		Run: func(cmd *cobra.Command, args []string) {
 			status := func() int {
 				const debugname = "debug"
-				goBuild := exec.Command("go", "build", "-o", debugname, "-gcflags", "-N -l")
-				goBuild.Stderr = os.Stderr
-				err := goBuild.Run()
-				if err != nil {
-					return 1
-				}
-				fp, err := filepath.Abs("./" + debugname)
-				if err != nil {
-					fmt.Fprintf(os.Stderr, err.Error())
-					return 1
-				}
-				defer os.Remove(fp)
+				var processArgs []string
+				if traceAttachPid == 0 {
+					goBuild := exec.Command("go", "build", "-o", debugname, "-gcflags", "-N -l")
+					goBuild.Stderr = os.Stderr
+					err := goBuild.Run()
+					if err != nil {
+						return 1
+					}
+					fp, err := filepath.Abs("./" + debugname)
+					if err != nil {
+						fmt.Fprintf(os.Stderr, err.Error())
+						return 1
+					}
+					defer os.Remove(fp)
 
-				processArgs := append([]string{"./" + debugname}, args...)
+					processArgs = append([]string{"./" + debugname}, args...)
+				}
 				// Make a TCP listener
 				listener, err := net.Listen("tcp", Addr)
 				if err != nil {
@@ -118,6 +122,7 @@ starts and attaches to it, and enables you to immediately begin debugging your p
 				server := rpc.NewServer(&service.Config{
 					Listener:    listener,
 					ProcessArgs: processArgs,
+					AttachPid:   traceAttachPid,
 				}, Log)
 				if err := server.Run(); err != nil {
 					fmt.Fprintln(os.Stderr, err)
@@ -158,7 +163,7 @@ starts and attaches to it, and enables you to immediately begin debugging your p
 						}
 						fmt.Printf("%s(%s) %s:%d\n", fname, strings.Join(args, ", "), state.CurrentThread.File, state.CurrentThread.Line)
 					case <-sigChan:
-						server.Stop(true)
+						server.Stop(traceAttachPid == 0)
 						return 1
 					}
 				}
@@ -167,6 +172,7 @@ starts and attaches to it, and enables you to immediately begin debugging your p
 			os.Exit(status)
 		},
 	}
+	traceCommand.Flags().IntVarP(&traceAttachPid, "pid", "p", 0, "Pid to attach to.")
 	rootCommand.AddCommand(traceCommand)
 
 	// 'test' subcommand.
diff --git a/proc/proc.go b/proc/proc.go
index 5d1971cc..6da4c2db 100644
--- a/proc/proc.go
+++ b/proc/proc.go
@@ -90,6 +90,11 @@ func Attach(pid int) (*Process, error) {
 
 // Detach from the process being debugged, optionally killing it.
 func (dbp *Process) Detach(kill bool) (err error) {
+	if dbp.Running() {
+		if err = dbp.Halt(); err != nil {
+			return
+		}
+	}
 	if !kill {
 		// Clean up any breakpoints we've set.
 		for _, bp := range dbp.Breakpoints {
-- 
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