github.com/mdempsky/go@v0.0.0-20151201204031-5dd372bd1e70/src/bytes/equal_test.go (about)

     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  }