pkg/proc: fix ebpf probe tracing backen uprobe handling (#3417)

Uprobes get automatically cleaned and removed when the reference to
the Link object is lost. Hold a reference to any active Uprobe Link
for duration of Delve execution and ensure they are cleaned up
at exit.

Fixes ebpf probes don't work after time.Sleep() #3227

_fixtures/ebpf_trace2.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func main() {
+	i := int64(0)
+	for i = 0; i < 5; i++ {
+		tracedFunction(i)
+	}
+	for i = 5; i < 10; i++ {
+		tracedFunction(i)
+		time.Sleep(time.Second)
+	}
+}
+
+//go:noinline
+func tracedFunction(x int64) {
+	fmt.Println(x)
+}

cmd/dlv/dlv_test.go

@@ -1157,6 +1157,54 @@ func TestTraceEBPF2(t *testing.T) {
 	cmd.Wait()
 }
 
+func TestTraceEBPF3(t *testing.T) {
+	if os.Getenv("CI") == "true" {
+		t.Skip("cannot run test in CI, requires kernel compiled with btf support")
+	}
+	if runtime.GOOS != "linux" || runtime.GOARCH != "amd64" {
+		t.Skip("not implemented on non linux/amd64 systems")
+	}
+	if !goversion.VersionAfterOrEqual(runtime.Version(), 1, 16) {
+		t.Skip("requires at least Go 1.16 to run test")
+	}
+	usr, err := user.Current()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if usr.Uid != "0" {
+		t.Skip("test must be run as root")
+	}
+
+	dlvbin := getDlvBinEBPF(t)
+
+	expected := []byte(`> (1) main.tracedFunction(0)
+> (1) main.tracedFunction(1)
+> (1) main.tracedFunction(2)
+> (1) main.tracedFunction(3)
+> (1) main.tracedFunction(4)
+> (1) main.tracedFunction(5)
+> (1) main.tracedFunction(6)
+> (1) main.tracedFunction(7)
+> (1) main.tracedFunction(8)
+> (1) main.tracedFunction(9)`)
+
+	fixtures := protest.FindFixturesDir()
+	cmd := exec.Command(dlvbin, "trace", "--ebpf", "--output", filepath.Join(t.TempDir(), "__debug"), filepath.Join(fixtures, "ebpf_trace2.go"), "main.traced")
+	rdr, err := cmd.StderrPipe()
+	assertNoError(err, t, "stderr pipe")
+	defer rdr.Close()
+
+	assertNoError(cmd.Start(), t, "running trace")
+
+	output, err := ioutil.ReadAll(rdr)
+	assertNoError(err, t, "ReadAll")
+
+	if !bytes.Contains(output, expected) {
+		t.Fatalf("expected:\n%s\ngot:\n%s", string(expected), string(output))
+	}
+	cmd.Wait()
+}
+
 func TestDlvTestChdir(t *testing.T) {
 	dlvbin := getDlvBin(t)
 

pkg/proc/internal/ebpf/helpers.go

@@ -61,6 +61,7 @@ type EBPFContext struct {
 	bpfRingBuf *ringbuf.Reader
 	executable *link.Executable
 	bpfArgMap  *ebpf.Map
+	links      []link.Link
 
 	parsedBpfEvents []RawUProbeParams
 	m               sync.Mutex
@@ -70,13 +71,19 @@ func (ctx *EBPFContext) Close() {
 	if ctx.objs != nil {
 		ctx.objs.Close()
 	}
+	if ctx.links != nil {
+		for _, l := range ctx.links {
+			l.Close()
+		}
+	}
 }
 
 func (ctx *EBPFContext) AttachUprobe(pid int, name string, offset uint64) error {
 	if ctx.executable == nil {
 		return errors.New("no eBPF program loaded")
 	}
-	_, err := ctx.executable.Uprobe(name, ctx.objs.tracePrograms.UprobeDlvTrace, &link.UprobeOptions{PID: pid, Offset: offset})
+	l, err := ctx.executable.Uprobe(name, ctx.objs.tracePrograms.UprobeDlvTrace, &link.UprobeOptions{PID: pid, Offset: offset})
+	ctx.links = append(ctx.links, l)
 	return err
 }