From 95b4498ac0c70a2c3c2a0c60d66aa74b10bca76d Mon Sep 17 00:00:00 2001
From: Ian Lance Taylor <iant@golang.org>
Date: Wed, 11 Apr 2018 14:16:52 -0700
Subject: [PATCH] cmd/internal/obj/arm64: don't crash on trailing NOP
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Fixes #20348

Change-Id: I831aeeee8e20d55b3e47dea67786e883b213cd58
Reviewed-on: https://go-review.googlesource.com/106457
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
---
 src/cmd/internal/obj/arm64/asm_test.go | 18 ++++++++++++++++++
 src/cmd/internal/obj/arm64/obj7.go     |  8 +++++---
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/cmd/internal/obj/arm64/asm_test.go b/src/cmd/internal/obj/arm64/asm_test.go
index 3e0c9c13a6..68f5b0b346 100644
--- a/src/cmd/internal/obj/arm64/asm_test.go
+++ b/src/cmd/internal/obj/arm64/asm_test.go
@@ -61,3 +61,21 @@ func gen(buf *bytes.Buffer) {
 	fmt.Fprintln(buf, "label:")
 	fmt.Fprintln(buf, "RET")
 }
+
+// Issue 20348.
+func TestNoRet(t *testing.T) {
+	dir, err := ioutil.TempDir("", "testnoret")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+	tmpfile := filepath.Join(dir, "x.s")
+	if err := ioutil.WriteFile(tmpfile, []byte("TEXT ·stub(SB),$0-0\nNOP\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	cmd := exec.Command(testenv.GoToolPath(t), "tool", "asm", "-o", filepath.Join(dir, "x.o"), tmpfile)
+	cmd.Env = []string{"GOARCH=arm64", "GOOS=linux"}
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Errorf("%v\n%s", err, out)
+	}
+}
diff --git a/src/cmd/internal/obj/arm64/obj7.go b/src/cmd/internal/obj/arm64/obj7.go
index 1bd4a5d7b1..9c3d22050e 100644
--- a/src/cmd/internal/obj/arm64/obj7.go
+++ b/src/cmd/internal/obj/arm64/obj7.go
@@ -476,9 +476,11 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			break
 
 		case obj.ANOP:
-			q1 = p.Link
-			q.Link = q1 /* q is non-nop */
-			q1.Mark |= p.Mark
+			if p.Link != nil {
+				q1 = p.Link
+				q.Link = q1 /* q is non-nop */
+				q1.Mark |= p.Mark
+			}
 			continue
 
 		case ABL,
-- 
2.48.1