// 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 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() q := dangerousSlice(t) if len(q) > 64 { // Only worry about when we're near the end of a page. q = q[len(q)-64:] } 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 } // Test differing alignments and sizes of q which always end on a page boundary. q[len(q)-1] = 1 // difference is only found on the last byte for j := 0; j < len(q); j++ { 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[len(q)-1] = 0 } func TestCountNearPageBoundary(t *testing.T) { t.Parallel() b := dangerousSlice(t) for i := range b { c := Count(b[i:], []byte{1}) if c != 0 { t.Fatalf("Count(b[%d:], {1})=%d, want 0\n", i, c) } c = Count(b[:i], []byte{0}) if c != i { t.Fatalf("Count(b[:%d], {0})=%d, want %d\n", i, c, i) } } }