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// Copyright 2017 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.
//
//go:build linux
// +build linux
package bytes_test
import (
. "bytes"
"syscall"
"testing"
)
// This file tests the situation where byte operations are checking
// data very near to a page boundary. We want to make sure those
// operations do not read across the boundary and cause a page
// fault where they shouldn't.
// These tests run only on linux. The code being tested is
// not OS-specific, so it does not need to be tested on all
// operating systems.
// dangerousSlice returns a slice which is immediately
// preceded and followed by a faulting page.
func dangerousSlice(t *testing.T) []byte {
pagesize := syscall.Getpagesize()
b, err := syscall.Mmap(0, 0, 3*pagesize, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_ANONYMOUS|syscall.MAP_PRIVATE)
if err != nil {
t.Fatalf("mmap failed %s", err)
}
err = syscall.Mprotect(b[:pagesize], syscall.PROT_NONE)
if err != nil {
t.Fatalf("mprotect low failed %s\n", err)
}
err = syscall.Mprotect(b[2*pagesize:], syscall.PROT_NONE)
if err != nil {
t.Fatalf("mprotect high failed %s\n", err)
}
return b[pagesize : 2*pagesize]
}
func TestEqualNearPageBoundary(t *testing.T) {
t.Parallel()
b := dangerousSlice(t)
for i := range b {
b[i] = 'A'
}
for i := 0; i <= len(b); i++ {
Equal(b[:i], b[len(b)-i:])
Equal(b[len(b)-i:], b[:i])
}
}
func TestIndexByteNearPageBoundary(t *testing.T) {
t.Parallel()
b := dangerousSlice(t)
for i := range b {
idx := IndexByte(b[i:], 1)
if idx != -1 {
t.Fatalf("IndexByte(b[%d:])=%d, want -1\n", i, idx)
}
}
}
func TestIndexNearPageBoundary(t *testing.T) {
t.Parallel()
var q [64]byte
b := dangerousSlice(t)
if len(b) > 256 {
// Only worry about when we're near the end of a page.
b = b[len(b)-256:]
}
for j := 1; j < len(q); j++ {
q[j-1] = 1 // difference is only found on the last byte
for i := range b {
idx := Index(b[i:], q[:j])
if idx != -1 {
t.Fatalf("Index(b[%d:], q[:%d])=%d, want -1\n", i, j, idx)
}
}
q[j-1] = 0
}
}
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