cmd/link: reject data size > 2 GB

We can't address more than this on amd64 anyway.

Fixes #9862.

Change-Id: Ifb1abae558e2e1ee2dc953a76995f3f08c60b1df
Reviewed-on: https://go-review.googlesource.com/11715
Reviewed-by: Austin Clements <austin@google.com>

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

@@ -1122,11 +1122,14 @@ func (p *GCProg) AddSym(s *LSym) {
 
 func growdatsize(datsizep *int64, s *LSym) {
 	datsize := *datsizep
-	if s.Size < 0 {
-		Diag("negative size (datsize = %d, s->size = %d)", datsize, s.Size)
-	}
-	if datsize+s.Size < datsize {
-		Diag("symbol too large (datsize = %d, s->size = %d)", datsize, s.Size)
+	const cutoff int64 = 2e9 // 2 GB (or so; looks better in errors than 2^31)
+	switch {
+	case s.Size < 0:
+		Diag("%s: negative size (%d bytes)", s.Name, s.Size)
+	case s.Size > cutoff:
+		Diag("%s: symbol too large (%d bytes)", s.Name, s.Size)
+	case datsize <= cutoff && datsize+s.Size > cutoff:
+		Diag("%s: too much data (over %d bytes)", s.Name, cutoff)
 	}
 	*datsizep = datsize + s.Size
 }

test/fixedbugs/issue9862.go

@@ -0,0 +1,15 @@
+// skip
+
+// Copyright 2015 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 main
+
+var a [1<<31 - 1024]byte
+
+func main() {
+	if a[0] != 0 {
+		panic("bad array")
+	}
+}

test/fixedbugs/issue9862_run.go

@@ -0,0 +1,27 @@
+// +build !nacl
+// run
+
+// Copyright 2015 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.
+
+// Check for compile or link error.
+
+package main
+
+import (
+	"os/exec"
+	"strings"
+)
+
+func main() {
+	out, err := exec.Command("go", "run", "fixedbugs/issue9862.go").CombinedOutput()
+	outstr := string(out)
+	if err == nil {
+		println("go run issue9862.go succeeded, should have failed\n", outstr)
+		return
+	}
+	if !strings.Contains(outstr, "symbol too large") {
+		println("go run issue9862.go gave unexpected error; want symbol too large:\n", outstr)
+	}
+}