arm64/arm64asm: avoid log.Fatal during test

Especially log.Fatal(err) where err came back from exec.Command.Run.
It prints no additional information and is very confusing for the test
to die printing 'exit status 1'.

For golang/go#21486.

Change-Id: I8675667838319a4d5697e596244bea514509894d
Reviewed-on: https://go-review.googlesource.com/56971
Run-TryBot: Russ Cox <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

Author: rsc

arm64/arm64asm/ext_test.go

@@ -503,7 +503,7 @@ func JSONCases(t *testing.T) func(func([]byte)) {
 	return func(try func([]byte)) {
 		data, err := ioutil.ReadFile("inst.json")
 		if err != nil {
-			log.Fatal(err)
+			t.Fatal(err)
 		}
 		var insts []InstJson
 		var instsN []InstJson
@@ -513,7 +513,7 @@ func JSONCases(t *testing.T) func(func([]byte)) {
 			N = 16
 		}
 		if err := json.Unmarshal(data, &insts); err != nil {
-			log.Fatal(err)
+			t.Fatal(err)
 		}
 		// Append instructions to get more test cases.
 		for i := 0; i < N; {

arm64/arm64asm/objdumpext_test.go

@@ -27,27 +27,19 @@ func testObjdumpARM64(t *testing.T, generate func(func([]byte))) {
 }
 
 func testObjdumpArch(t *testing.T, generate func(func([]byte)), arch Mode) {
-	if _, err := os.Stat(objdumpPath); err != nil {
-		t.Skip(err)
-	}
-	// Check objdump can disassemble elf64-aarch64.
-	if test := objdumpinfo(); test == false {
-		t.Skip("Skip the test if installed objdump doesn't support aarch64 elf format")
-	}
+	checkObjdumpAarch64(t)
 	testExtDis(t, "gnu", arch, objdump, generate, allowedMismatchObjdump)
 	testExtDis(t, "plan9", arch, objdump, generate, allowedMismatchObjdump)
 }
 
-func objdumpinfo() bool {
-	var i = []byte("aarch64")
+func checkObjdumpAarch64(t *testing.T) {
 	out, err := exec.Command(objdumpPath, "-i").Output()
 	if err != nil {
-		log.Fatal(err)
+		t.Skip("cannot run objdump: %v\n%s", err, out)
 	}
-	if bytes.Contains(out, i) {
-		return true
+	if !strings.Contains(string(out), "aarch64") {
+		t.Skip("objdump does not have aarch64 support")
 	}
-	return false
 }
 
 func objdump(ext *ExtDis) error {