[release-branch.go1.12] cmd/link: increase the function call limit in stkcheck

There is real (albeit generated) code that exceeds the limit.

Updates #33555
Fixes #33557

Change-Id: I668e85825d3d2a471970e869abe63f3492213cc1
Reviewed-on: https://go-review.googlesource.com/c/go/+/189697
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
(cherry picked from commit 951143cf)
Reviewed-on: https://go-review.googlesource.com/c/go/+/189717

src/cmd/link/internal/ld/lib.go

@@ -1966,7 +1966,7 @@ func stkcheck(ctxt *Link, up *chain, depth int) int {
 		s.Attr |= sym.AttrStackCheck
 	}
 
-	if depth > 100 {
+	if depth > 500 {
 		Errorf(s, "nosplit stack check too deep")
 		stkbroke(ctxt, up, 0)
 		return -1

test/fixedbugs/issue33555.go

+// +build !nacl,!js
+// run
+
+// 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.
+
+// Test that the linker permits long call sequences.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+)
+
+const start = `
+package main
+
+func main() {
+	println(f0() + 1)
+}
+`
+
+const fn = `
+//go:noinline
+func f%d() int {
+	return f%d() + 1
+}`
+
+const fnlast = `
+//go:noinline
+func f%d() int {
+	return 0
+}
+`
+
+const count = 400
+
+func main() {
+	if err := test(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func test() error {
+	var buf bytes.Buffer
+	buf.WriteString(start)
+	for i := 0; i < count; i++ {
+		fmt.Fprintf(&buf, fn, i, i + 1)
+	}
+	fmt.Fprintf(&buf, fnlast, count)
+
+	dir, err := ioutil.TempDir("", "issue33555")
+	if err != nil {
+		return err
+	}
+	defer os.RemoveAll(dir)
+
+	fn := filepath.Join(dir, "x.go")
+	if err := ioutil.WriteFile(fn, buf.Bytes(), 0644); err != nil {
+		return err
+	}
+
+	out, err := exec.Command("go", "run", fn).CombinedOutput()
+	if err != nil {
+		return err
+	}
+
+	want := strconv.Itoa(count + 1)
+	if got := string(bytes.TrimSpace(out)); got != want {
+		return fmt.Errorf("got %q want %q", got, want)
+	}
+
+	return nil
+}