cmd/internal/objfile: don't require runtime.symtab symbol for XCOFF

For some reason (that I didn't look into), externally linked
AIX binaries don't have runtime.symtab symbol. Since recent Go
releases (Go 1.3 maybe?), that symbol is empty and not necessary
anyway. Don't require it.

Fixes #40972.

Change-Id: I73a1f0142195ea6debdba8a4f6e12cadc3980dc5
Reviewed-on: https://go-review.googlesource.com/c/go/+/279995
Trust: Cherry Zhang <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>

Author: cherrymui

src/cmd/internal/objfile/xcoff.go

@@ -94,9 +94,7 @@ func (f *xcoffFile) pcln() (textStart uint64, symtab, pclntab []byte, err error)
 	if pclntab, err = loadXCOFFTable(f.xcoff, "runtime.pclntab", "runtime.epclntab"); err != nil {
 		return 0, nil, nil, err
 	}
-	if symtab, err = loadXCOFFTable(f.xcoff, "runtime.symtab", "runtime.esymtab"); err != nil {
-		return 0, nil, nil, err
-	}
+	symtab, _ = loadXCOFFTable(f.xcoff, "runtime.symtab", "runtime.esymtab") // ignore error, this symbol is not useful anyway
 	return textStart, symtab, pclntab, nil
 }
 

src/cmd/objdump/objdump_test.go

@@ -237,9 +237,6 @@ func testGoAndCgoDisasm(t *testing.T, printCode bool, printGnuAsm bool) {
 	t.Parallel()
 	testDisasm(t, "fmthello.go", printCode, printGnuAsm)
 	if build.Default.CgoEnabled {
-		if runtime.GOOS == "aix" {
-			return // issue 40972
-		}
 		testDisasm(t, "fmthellocgo.go", printCode, printGnuAsm)
 	}
 }
@@ -261,8 +258,6 @@ func TestDisasmExtld(t *testing.T) {
 	switch runtime.GOOS {
 	case "plan9", "windows":
 		t.Skipf("skipping on %s", runtime.GOOS)
-	case "aix":
-		t.Skipf("skipping on AIX, see issue 40972")
 	}
 	t.Parallel()
 	testDisasm(t, "fmthello.go", false, false, "-ldflags=-linkmode=external")