version/print.go

@@ -24,7 +24,14 @@ var stringLazy = sync.OnceValue(func() string {
 	if extraGitCommitStamp != "" {
 		fmt.Fprintf(&ret, "  other commit: %s\n", extraGitCommitStamp)
 	}
-	fmt.Fprintf(&ret, "  go version: %s\n", runtime.Version())
+	if tsGoRev := tailscaleToolchainRev(); tsGoRev != "" {
+		if len(tsGoRev) > 10 {
+			tsGoRev = tsGoRev[:10]
+		}
+		fmt.Fprintf(&ret, "  go version: %s (tailscale/go %s)\n", runtime.Version(), tsGoRev)
+	} else {
+		fmt.Fprintf(&ret, "  go version: %s\n", runtime.Version())
+	}
 	return strings.TrimSpace(ret.String())
 })
 

version/prop.go

@@ -312,6 +312,11 @@ type Meta struct {
 	// GitCommitTime is the commit time of the git commit in GitCommit.
 	GitCommitTime string `json:"gitCommitTime,omitempty"`
 
+	// TailscaleGoGitHash is the git commit hash from
+	// https://github.com/tailscale/go used to build this binary, if built
+	// with the Tailscale Go toolchain. Otherwise it is empty.
+	TailscaleGoGitHash string `json:"tailscaleGoGitHash,omitempty"`
+
 	// Cap is the current Tailscale capability version. It's a monotonically
 	// incrementing integer that's incremented whenever a new capability is
 	// added.
@@ -324,17 +329,18 @@ var getMeta lazy.SyncValue[Meta]
 func GetMeta() Meta {
 	return getMeta.Get(func() Meta {
 		return Meta{
-			MajorMinorPatch: majorMinorPatch(),
-			Short:           Short(),
-			Long:            Long(),
-			GitCommitTime:   getEmbeddedInfo().commitTime,
-			GitCommit:       gitCommit(),
-			GitDirty:        gitDirty(),
-			OSVariant:       osVariant(),
-			ExtraGitCommit:  extraGitCommitStamp,
-			IsDev:           isDev(),
-			UnstableBranch:  IsUnstableBuild(),
-			Cap:             int(tailcfg.CurrentCapabilityVersion),
+			MajorMinorPatch:    majorMinorPatch(),
+			Short:              Short(),
+			Long:               Long(),
+			GitCommitTime:      getEmbeddedInfo().commitTime,
+			GitCommit:          gitCommit(),
+			GitDirty:           gitDirty(),
+			OSVariant:          osVariant(),
+			ExtraGitCommit:     extraGitCommitStamp,
+			IsDev:              isDev(),
+			UnstableBranch:     IsUnstableBuild(),
+			TailscaleGoGitHash: tailscaleToolchainRev(),
+			Cap:                int(tailcfg.CurrentCapabilityVersion),
 		}
 	})
 }

version/version.go

@@ -146,6 +146,23 @@ var getEmbeddedInfo = sync.OnceValue(func() embeddedInfo {
 	return ret
 })
 
+// tailscaleToolchainRev returns the git hash of the Tailscale Go toolchain
+// used to build this binary, if any. It is read separately from getEmbeddedInfo
+// because that function discards build info when VCS fields are missing (e.g.
+// in test binaries), but the toolchain rev is still present.
+var tailscaleToolchainRev = sync.OnceValue(func() string {
+	bi, ok := debug.ReadBuildInfo()
+	if !ok {
+		return ""
+	}
+	for _, s := range bi.Settings {
+		if s.Key == "tailscale.toolchain.rev" {
+			return s.Value
+		}
+	}
+	return ""
+})
+
 func gitCommit() string {
 	if gitCommitStamp != "" {
 		return gitCommitStamp

version/version_internal_test.go

@@ -3,7 +3,13 @@
 
 package version
 
-import "testing"
+import (
+	"os/exec"
+	"strings"
+	"testing"
+
+	"tailscale.com/util/cibuild"
+)
 
 func TestIsValidLongWithTwoRepos(t *testing.T) {
 	tests := []struct {
@@ -26,6 +32,26 @@ func TestIsValidLongWithTwoRepos(t *testing.T) {
 	}
 }
 
+func TestTailscaleToolchainRev(t *testing.T) {
+	out, err := exec.Command("go", "env", "GOROOT").Output()
+	if err != nil {
+		t.Fatalf("go env GOROOT: %v", err)
+	}
+	goRoot := strings.TrimSpace(string(out))
+	isTsgo := strings.Contains(goRoot, "/.cache/tsgo/")
+	if !cibuild.On() && !isTsgo {
+		t.Skip("skipping; not in CI and not using the Tailscale Go toolchain")
+	}
+	if !isTailscaleGo {
+		t.Skip("skipping; not built with tailscale_go build tag")
+	}
+	rev := tailscaleToolchainRev()
+	if rev == "" {
+		t.Fatal("tailscale.toolchain.rev is empty in build info; expected non-empty when using tsgo")
+	}
+	t.Logf("tailscale.toolchain.rev = %s", rev)
+}
+
 func TestPrepExeNameForCmp(t *testing.T) {
 	cases := []struct {
 		exe  string