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Source file src/bytes/equal_test.go

Documentation: bytes

  // Copyright 2013 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.
  //
  // +build linux
  
  package bytes_test
  
  import (
  	. "bytes"
  	"syscall"
  	"testing"
  	"unsafe"
  )
  
  // This file tests the situation where memeq is checking
  // data very near to a page boundary. We want to make sure
  // equal does not read across the boundary and cause a page
  // fault where it shouldn't.
  
  // This test runs only on linux. The code being tested is
  // not OS-specific, so it does not need to be tested on all
  // operating systems.
  
  func TestEqualNearPageBoundary(t *testing.T) {
  	pagesize := syscall.Getpagesize()
  	b := make([]byte, 4*pagesize)
  	i := pagesize
  	for ; uintptr(unsafe.Pointer(&b[i]))%uintptr(pagesize) != 0; i++ {
  	}
  	syscall.Mprotect(b[i-pagesize:i], 0)
  	syscall.Mprotect(b[i+pagesize:i+2*pagesize], 0)
  	defer syscall.Mprotect(b[i-pagesize:i], syscall.PROT_READ|syscall.PROT_WRITE)
  	defer syscall.Mprotect(b[i+pagesize:i+2*pagesize], syscall.PROT_READ|syscall.PROT_WRITE)
  
  	// both of these should fault
  	//pagesize += int(b[i-1])
  	//pagesize += int(b[i+pagesize])
  
  	for j := 0; j < pagesize; j++ {
  		b[i+j] = 'A'
  	}
  	for j := 0; j <= pagesize; j++ {
  		Equal(b[i:i+j], b[i+pagesize-j:i+pagesize])
  		Equal(b[i+pagesize-j:i+pagesize], b[i:i+j])
  	}
  }
  

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