cmd/internal/obj/riscv: handle call, jmp and branch

Also provide REG_LR to more clearly define the link register.

Based on the riscv-go port.

Updates #27532

Change-Id: I0805f373682f93b3918a01c21d4ef34eb3817c75
Reviewed-on: https://go-review.googlesource.com/c/go/+/204627
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/obj/riscv/asm_test.go

@@ -0,0 +1,79 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package riscv
+
+import (
+	"bytes"
+	"fmt"
+	"internal/testenv"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+// TestLarge generates a very large file to verify that large
+// program builds successfully, in particular, too-far
+// conditional branches are fixed.
+func TestLarge(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Skip in short mode")
+	}
+	testenv.MustHaveGoBuild(t)
+
+	dir, err := ioutil.TempDir("", "testlarge")
+	if err != nil {
+		t.Fatalf("could not create directory: %v", err)
+	}
+	defer os.RemoveAll(dir)
+
+	// Generate a very large function.
+	buf := bytes.NewBuffer(make([]byte, 0, 7000000))
+	gen(buf)
+
+	tmpfile := filepath.Join(dir, "x.s")
+	err = ioutil.WriteFile(tmpfile, buf.Bytes(), 0644)
+	if err != nil {
+		t.Fatalf("can't write output: %v\n", err)
+	}
+
+	// Build generated file.
+	cmd := exec.Command(testenv.GoToolPath(t), "tool", "asm", "-o", filepath.Join(dir, "x.o"), tmpfile)
+	cmd.Env = append(os.Environ(), "GOARCH=riscv64", "GOOS=linux")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Errorf("Build failed: %v, output: %s", err, out)
+	}
+}
+
+// gen generates a very large program, with a very far conditional branch.
+func gen(buf *bytes.Buffer) {
+	fmt.Fprintln(buf, "TEXT f(SB),0,$0-0")
+	fmt.Fprintln(buf, "BEQ X0, X0, label")
+	for i := 0; i < 1<<19; i++ {
+		fmt.Fprintln(buf, "ADD $0, X0, X0")
+	}
+	fmt.Fprintln(buf, "label:")
+	fmt.Fprintln(buf, "ADD $0, X0, X0")
+}
+
+// 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 = append(os.Environ(), "GOARCH=riscv64", "GOOS=linux")
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Errorf("%v\n%s", err, out)
+	}
+}