cmd/internal/objfile: emit better error for Go object of a different version

The Go object file format can change from version to version.
Tools like cmd/objdump and cmd/nm only onderstand the current
version of the object file. Currently, when it encounters an
object built with a different version of the toolchain, it emits
a generic error "unrecognized object file", which is not very
helpful for users. This CL makes it emit a clearer error. Now it
emits

objdump: open go116.o: go object of a different version: go116ld

Change-Id: I063c6078ed1da78f97cea65796779ae093a1a8cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/315609
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

2 files changed, 15 insertions, 0 deletions

diff --git a/src/cmd/objdump/objdump_test.go b/src/cmd/objdump/objdump_test.go
index ac184441ea..f231a7c6e0 100644
--- a/src/cmd/objdump/objdump_test.go
+++ b/src/cmd/objdump/objdump_test.go
@@ -345,3 +345,18 @@ func TestGoobjFileNumber(t *testing.T) {
 		t.Logf("output:\n%s", text)
 	}
 }
+
+func TestGoObjOtherVersion(t *testing.T) {
+	testenv.MustHaveExec(t)
+	t.Parallel()
+
+	obj := filepath.Join("testdata", "go116.o")
+	cmd := exec.Command(exe, obj)
+	out, err := cmd.CombinedOutput()
+	if err == nil {
+		t.Fatalf("objdump go116.o succeeded unexpectly")
+	}
+	if !strings.Contains(string(out), "go object of a different version") {
+		t.Errorf("unexpected error message:\n%s", out)
+	}
+}
diff --git a/src/cmd/objdump/testdata/go116.o b/src/cmd/objdump/testdata/go116.o
new file mode 100644
index 0000000000..6434d5c8cf
--- /dev/null
+++ b/src/cmd/objdump/testdata/go116.o