From c9c64886ef041b096d7f93c4e7d2ef5faf87ad43 Mon Sep 17 00:00:00 2001
From: Cherry Zhang <cherryyz@google.com>
Date: Mon, 19 Oct 2020 10:40:24 -0400
Subject: [PATCH] cmd/internal/obj: reject too large symbols

We never supported symbol larger than 2GB (issue #9862), so the
object file uses 32-bit for symbol sizes. Check and reject too
large symbol before truncating its size.

Fixes #42054.

Change-Id: I0d1d585ebdba9556f2fd3a97043bd4296d5cc9e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/263641
Trust: Cherry Zhang <cherryyz@google.com>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
---
 src/cmd/internal/obj/objfile.go      |  7 ++++++
 src/cmd/internal/obj/objfile_test.go | 36 ++++++++++++++++++++++++++++
 test/fixedbugs/issue4348.go          |  4 +++-
 3 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index a08de891d3..a24a7b878f 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -261,6 +261,10 @@ func (w *writer) StringTable() {
 	}
 }
 
+// cutoff is the maximum data section size permitted by the linker
+// (see issue #9862).
+const cutoff = int64(2e9) // 2 GB (or so; looks better in errors than 2^31)
+
 func (w *writer) Sym(s *LSym) {
 	abi := uint16(s.ABI())
 	if s.Static() {
@@ -325,6 +329,9 @@ func (w *writer) Sym(s *LSym) {
 			// don't bother setting align to 1.
 		}
 	}
+	if s.Size > cutoff {
+		w.ctxt.Diag("%s: symbol too large (%d bytes > %d bytes)", s.Name, s.Size, cutoff)
+	}
 	var o goobj.Sym
 	o.SetName(name, w.Writer)
 	o.SetABI(abi)
diff --git a/src/cmd/internal/obj/objfile_test.go b/src/cmd/internal/obj/objfile_test.go
index 155701fa4e..146627b62b 100644
--- a/src/cmd/internal/obj/objfile_test.go
+++ b/src/cmd/internal/obj/objfile_test.go
@@ -5,9 +5,16 @@
 package obj
 
 import (
+	"bytes"
 	"cmd/internal/goobj"
 	"cmd/internal/sys"
+	"internal/testenv"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
 	"testing"
+	"unsafe"
 )
 
 var dummyArch = LinkArch{Arch: sys.ArchAMD64}
@@ -85,3 +92,32 @@ func TestContentHash(t *testing.T) {
 		}
 	}
 }
+
+func TestSymbolTooLarge(t *testing.T) { // Issue 42054
+	testenv.MustHaveGoBuild(t)
+	if unsafe.Sizeof(uintptr(0)) < 8 {
+		t.Skip("skip on 32-bit architectures")
+	}
+
+	tmpdir, err := ioutil.TempDir("", "TestSymbolTooLarge")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpdir)
+
+	src := filepath.Join(tmpdir, "p.go")
+	err = ioutil.WriteFile(src, []byte("package p; var x [1<<32]byte"), 0666)
+	if err != nil {
+		t.Fatalf("failed to write source file: %v\n", err)
+	}
+	obj := filepath.Join(tmpdir, "p.o")
+	cmd := exec.Command(testenv.GoToolPath(t), "tool", "compile", "-o", obj, src)
+	out, err := cmd.CombinedOutput()
+	if err == nil {
+		t.Fatalf("did not fail\noutput: %s", out)
+	}
+	const want = "symbol too large"
+	if !bytes.Contains(out, []byte(want)) {
+		t.Errorf("unexpected error message: want: %q, got: %s", want, out)
+	}
+}
diff --git a/test/fixedbugs/issue4348.go b/test/fixedbugs/issue4348.go
index c59b6b8caa..8b1a56c1d5 100644
--- a/test/fixedbugs/issue4348.go
+++ b/test/fixedbugs/issue4348.go
@@ -1,4 +1,4 @@
-// compile
+// skip
 
 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -7,6 +7,8 @@
 // Issue 4348. After switch to 64-bit ints the compiler generates
 // illegal instructions when using large array bounds or indexes.
 
+// Skip. We reject symbols larger that 2GB (Issue #9862).
+
 package main
 
 // 1<<32 on a 64-bit machine, 1 otherwise.