cmd/compile: fix spurious R_TLE_LE reloc on android/386

When compiling for GOARCH=386 GOOS=android, the compiler was attaching
R_TLS_LE relocations inappropriately -- as of Go 1.13 the TLS access
recipe for Android refers to a runtime symbol and no longer needs this
type of relocation (which was causing a crash when the linker tried to
process it).

Updates #29674.
Fixes #34788.

Change-Id: Ida01875011b524586597b1f7e273aa14e11815d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/200337
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Elias Naur <mail@eliasnaur.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/internal/obj/x86/asm6.go

@@ -3468,7 +3468,7 @@ func (ab *AsmBuf) asmandsz(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, a *obj
 	}
 
 	if REG_AX <= base && base <= REG_R15 {
-		if a.Index == REG_TLS && !ctxt.Flag_shared {
+		if a.Index == REG_TLS && !ctxt.Flag_shared && !isAndroid {
 			rel = obj.Reloc{}
 			rel.Type = objabi.R_TLS_LE
 			rel.Siz = 4

src/cmd/link/link_test.go

 package main
 
 import (
+	"bufio"
+	"bytes"
 	"debug/macho"
 	"internal/testenv"
 	"io/ioutil"
@@ -315,3 +317,62 @@ func TestMacOSVersion(t *testing.T) {
 		t.Errorf("no LC_VERSION_MIN_MACOSX load command found")
 	}
 }
+
+const Issue34788src = `
+
+package blah
+
+func Blah(i int) int {
+	a := [...]int{1, 2, 3, 4, 5, 6, 7, 8}
+	return a[i&7]
+}
+`
+
+func TestIssue34788Android386TLSSequence(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This is a cross-compilation test, so it doesn't make
+	// sense to run it on every GOOS/GOARCH combination. Limit
+	// the test to amd64 + darwin/linux.
+	if runtime.GOARCH != "amd64" ||
+		(runtime.GOOS != "darwin" && runtime.GOOS != "linux") {
+		t.Skip("skipping on non-{linux,darwin}/amd64 platform")
+	}
+
+	tmpdir, err := ioutil.TempDir("", "TestIssue34788Android386TLSSequence")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpdir)
+
+	src := filepath.Join(tmpdir, "blah.go")
+	err = ioutil.WriteFile(src, []byte(Issue34788src), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	obj := filepath.Join(tmpdir, "blah.o")
+	cmd := exec.Command(testenv.GoToolPath(t), "tool", "compile", "-o", obj, src)
+	cmd.Env = append(os.Environ(), "GOARCH=386", "GOOS=android")
+	if out, err := cmd.CombinedOutput(); err != nil {
+		if err != nil {
+			t.Fatalf("failed to compile blah.go: %v, output: %s\n", err, out)
+		}
+	}
+
+	// Run objdump on the resulting object.
+	cmd = exec.Command(testenv.GoToolPath(t), "tool", "objdump", obj)
+	out, oerr := cmd.CombinedOutput()
+	if oerr != nil {
+		t.Fatalf("failed to objdump blah.o: %v, output: %s\n", oerr, out)
+	}
+
+	// Sift through the output; we should not be seeing any R_TLS_LE relocs.
+	scanner := bufio.NewScanner(bytes.NewReader(out))
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.Contains(line, "R_TLS_LE") {
+			t.Errorf("objdump output contains unexpected R_TLS_LE reloc: %s", line)
+		}
+	}
+}