libgo/go/bytes/equal_test.go

   1 // Copyright 2013 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4 //
   5 // +build linux
   6
   7 package bytes_test
   8
   9 import (
  10         . "bytes"
  11         "syscall"
  12         "testing"
  13         "unsafe"
  14 )
  15
  16 // This file tests the situation where memeq is checking
  17 // data very near to a page boundary. We want to make sure
  18 // equal does not read across the boundary and cause a page
  19 // fault where it shouldn't.
  20
  21 // This test runs only on linux. The code being tested is
  22 // not OS-specific, so it does not need to be tested on all
  23 // operating systems.
  24
  25 func TestEqualNearPageBoundary(t *testing.T) {
  26         pagesize := syscall.Getpagesize()
  27         b := make([]byte, 4*pagesize)
  28         i := pagesize
  29         for ; uintptr(unsafe.Pointer(&b[i]))%uintptr(pagesize) != 0; i++ {
  30         }
  31         syscall.Mprotect(b[i-pagesize:i], 0)
  32         syscall.Mprotect(b[i+pagesize:i+2*pagesize], 0)
  33         defer syscall.Mprotect(b[i-pagesize:i], syscall.PROT_READ|syscall.PROT_WRITE)
  34         defer syscall.Mprotect(b[i+pagesize:i+2*pagesize], syscall.PROT_READ|syscall.PROT_WRITE)
  35
  36         // both of these should fault
  37         //pagesize += int(b[i-1])
  38         //pagesize += int(b[i+pagesize])
  39
  40         for j := 0; j < pagesize; j++ {
  41                 b[i+j] = 'A'
  42         }
  43         for j := 0; j <= pagesize; j++ {
  44                 Equal(b[i:i+j], b[i+pagesize-j:i+pagesize])
  45                 Equal(b[i+pagesize-j:i+pagesize], b[i:i+j])
  46         }
  47 }