1 // Copyright 2017 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 ) 14 15 // This file tests the situation where byte operations are checking 16 // data very near to a page boundary. We want to make sure those 17 // operations do not read across the boundary and cause a page 18 // fault where they shouldn't. 19 20 // These tests run only on linux. The code being tested is 21 // not OS-specific, so it does not need to be tested on all 22 // operating systems. 23 24 // dangerousSlice returns a slice which is immediately 25 // preceded and followed by a faulting page. 26 func dangerousSlice(t *testing.T) []byte { 27 pagesize := syscall.Getpagesize() 28 b, err := syscall.Mmap(0, 0, 3*pagesize, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_ANONYMOUS|syscall.MAP_PRIVATE) 29 if err != nil { 30 t.Fatalf("mmap failed %s", err) 31 } 32 err = syscall.Mprotect(b[:pagesize], syscall.PROT_NONE) 33 if err != nil { 34 t.Fatalf("mprotect low failed %s\n", err) 35 } 36 err = syscall.Mprotect(b[2*pagesize:], syscall.PROT_NONE) 37 if err != nil { 38 t.Fatalf("mprotect high failed %s\n", err) 39 } 40 return b[pagesize : 2*pagesize] 41 } 42 43 func TestEqualNearPageBoundary(t *testing.T) { 44 t.Parallel() 45 b := dangerousSlice(t) 46 for i := range b { 47 b[i] = 'A' 48 } 49 for i := 0; i <= len(b); i++ { 50 Equal(b[:i], b[len(b)-i:]) 51 Equal(b[len(b)-i:], b[:i]) 52 } 53 } 54 55 func TestIndexByteNearPageBoundary(t *testing.T) { 56 t.Parallel() 57 b := dangerousSlice(t) 58 for i := range b { 59 idx := IndexByte(b[i:], 1) 60 if idx != -1 { 61 t.Fatalf("IndexByte(b[%d:])=%d, want -1\n", i, idx) 62 } 63 } 64 } 65 66 func TestIndexNearPageBoundary(t *testing.T) { 67 t.Parallel() 68 var q [64]byte 69 b := dangerousSlice(t) 70 if len(b) > 256 { 71 // Only worry about when we're near the end of a page. 72 b = b[len(b)-256:] 73 } 74 for j := 1; j < len(q); j++ { 75 q[j-1] = 1 // difference is only found on the last byte 76 for i := range b { 77 idx := Index(b[i:], q[:j]) 78 if idx != -1 { 79 t.Fatalf("Index(b[%d:], q[:%d])=%d, want -1\n", i, j, idx) 80 } 81 } 82 q[j-1] = 0 83 } 84 } 85
