misc/cgo/test: set the traceback level instead of failing the test

Previously, test7978 failed if the user did not invoke it with
GOTRACEBACK=2 already set in their environment. Environment-sensitive
test are awkward, and in this case there is a very simple workaround:
set the traceback level to the necessary value explicitly.

Change-Id: I7d576f24138aa8a41392148eae11bbeaef558573
Reviewed-on: https://go-review.googlesource.com/63275
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/test/issue7978.go

@@ -44,8 +44,8 @@ static void issue7978c(uint32_t *sync) {
 import "C"
 
 import (
-	"os"
 	"runtime"
+	"runtime/debug"
 	"strings"
 	"sync/atomic"
 	"testing"
@@ -114,12 +114,7 @@ func test7978(t *testing.T) {
 	if C.HAS_SYNC_FETCH_AND_ADD == 0 {
 		t.Skip("clang required for __sync_fetch_and_add support on darwin/arm")
 	}
-	if runtime.GOOS == "android" || runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64") {
-		t.Skip("GOTRACEBACK is not passed on to the exec wrapper")
-	}
-	if os.Getenv("GOTRACEBACK") != "2" {
-		t.Fatalf("GOTRACEBACK must be 2")
-	}
+	debug.SetTraceback("2")
 	issue7978sync = 0
 	go issue7978go()
 	// test in c code, before callback

src/cmd/dist/test.go

@@ -874,14 +874,10 @@ func (t *tester) runHostTest(dir, pkg string) error {
 }
 
 func (t *tester) cgoTest(dt *distTest) error {
-	env := append(os.Environ(), "GOTRACEBACK=2")
-
-	cmd := t.addCmd(dt, "misc/cgo/test", "go", "test", t.tags(), "-ldflags", "-linkmode=auto", t.runFlag(""))
-	cmd.Env = env
+	t.addCmd(dt, "misc/cgo/test", "go", "test", t.tags(), "-ldflags", "-linkmode=auto", t.runFlag(""))
 
 	if t.internalLink() {
-		cmd := t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", "-linkmode=internal", t.runFlag(""))
-		cmd.Env = env
+		t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", "-linkmode=internal", t.runFlag(""))
 	}
 
 	pair := t.gohostos + "-" + t.goarch
@@ -893,24 +889,17 @@ func (t *tester) cgoTest(dt *distTest) error {
 		if !t.extLink() {
 			break
 		}
-		cmd := t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", "-linkmode=external")
-		cmd.Env = env
-		cmd = t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", "-linkmode=external -s")
-		cmd.Env = env
+		t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", "-linkmode=external")
+		t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", "-linkmode=external -s")
 	case "android-arm",
 		"dragonfly-386", "dragonfly-amd64",
 		"freebsd-386", "freebsd-amd64", "freebsd-arm",
 		"linux-386", "linux-amd64", "linux-arm", "linux-ppc64le", "linux-s390x",
 		"netbsd-386", "netbsd-amd64":
 
-		cmd := t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", "-linkmode=external")
-		cmd.Env = env
-
-		cmd = t.addCmd(dt, "misc/cgo/testtls", "go", "test", "-ldflags", "-linkmode=auto")
-		cmd.Env = env
-
-		cmd = t.addCmd(dt, "misc/cgo/testtls", "go", "test", "-ldflags", "-linkmode=external")
-		cmd.Env = env
+		t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", "-linkmode=external")
+		t.addCmd(dt, "misc/cgo/testtls", "go", "test", "-ldflags", "-linkmode=auto")
+		t.addCmd(dt, "misc/cgo/testtls", "go", "test", "-ldflags", "-linkmode=external")
 
 		switch pair {
 		case "netbsd-386", "netbsd-amd64":
@@ -925,45 +914,30 @@ func (t *tester) cgoTest(dt *distTest) error {
 			cc := mustEnv("CC")
 			cmd := t.dirCmd("misc/cgo/test",
 				cc, "-xc", "-o", "/dev/null", "-static", "-")
-			cmd.Env = env
 			cmd.Stdin = strings.NewReader("int main() {}")
 			if err := cmd.Run(); err != nil {
 				fmt.Println("No support for static linking found (lacks libc.a?), skip cgo static linking test.")
 			} else {
 				if t.goos != "android" {
-					cmd = t.addCmd(dt, "misc/cgo/testtls", "go", "test", "-ldflags", `-linkmode=external -extldflags "-static -pthread"`)
-					cmd.Env = env
+					t.addCmd(dt, "misc/cgo/testtls", "go", "test", "-ldflags", `-linkmode=external -extldflags "-static -pthread"`)
 				}
-
-				cmd = t.addCmd(dt, "misc/cgo/nocgo", "go", "test")
-				cmd.Env = env
-
-				cmd = t.addCmd(dt, "misc/cgo/nocgo", "go", "test", "-ldflags", `-linkmode=external`)
-				cmd.Env = env
-
+				t.addCmd(dt, "misc/cgo/nocgo", "go", "test")
+				t.addCmd(dt, "misc/cgo/nocgo", "go", "test", "-ldflags", `-linkmode=external`)
 				if t.goos != "android" {
-					cmd = t.addCmd(dt, "misc/cgo/nocgo", "go", "test", "-ldflags", `-linkmode=external -extldflags "-static -pthread"`)
-					cmd.Env = env
+					t.addCmd(dt, "misc/cgo/nocgo", "go", "test", "-ldflags", `-linkmode=external -extldflags "-static -pthread"`)
 				}
 			}
 
 			if pair != "freebsd-amd64" { // clang -pie fails to link misc/cgo/test
 				cmd := t.dirCmd("misc/cgo/test",
 					cc, "-xc", "-o", "/dev/null", "-pie", "-")
-				cmd.Env = env
 				cmd.Stdin = strings.NewReader("int main() {}")
 				if err := cmd.Run(); err != nil {
 					fmt.Println("No support for -pie found, skip cgo PIE test.")
 				} else {
-					cmd = t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", `-linkmode=external -extldflags "-pie"`)
-					cmd.Env = env
-
-					cmd = t.addCmd(dt, "misc/cgo/testtls", "go", "test", "-ldflags", `-linkmode=external -extldflags "-pie"`)
-					cmd.Env = env
-
-					cmd = t.addCmd(dt, "misc/cgo/nocgo", "go", "test", "-ldflags", `-linkmode=external -extldflags "-pie"`)
-					cmd.Env = env
-
+					t.addCmd(dt, "misc/cgo/test", "go", "test", "-ldflags", `-linkmode=external -extldflags "-pie"`)
+					t.addCmd(dt, "misc/cgo/testtls", "go", "test", "-ldflags", `-linkmode=external -extldflags "-pie"`)
+					t.addCmd(dt, "misc/cgo/nocgo", "go", "test", "-ldflags", `-linkmode=external -extldflags "-pie"`)
 				}
 			}
 		}