1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #pragma once
18 
19 #include <stddef.h>
20 #include <stdint.h>
21 #include <sys/auxv.h>
22 
23 // For PAGE_SIZE.
24 #include <sys/user.h>
25 
page_size()26 inline size_t page_size() {
27 #if defined(PAGE_SIZE)
28   return PAGE_SIZE;
29 #else
30   static const size_t page_size = getauxval(AT_PAGESZ);
31   return page_size;
32 #endif
33 }
34 
35 // The maximum page size supported on any Android device. As
36 // of API level 35, this is limited by ART.
max_android_page_size()37 constexpr size_t max_android_page_size() {
38 #if defined(PAGE_SIZE)
39   return PAGE_SIZE;
40 #else
41   return 16384;
42 #endif
43 }
44 
45 // Returns the address of the page containing address 'x'.
page_start(uintptr_t x)46 inline uintptr_t page_start(uintptr_t x) {
47   return x & ~(page_size() - 1);
48 }
49 
50 // Returns the offset of address 'x' in its page.
page_offset(uintptr_t x)51 inline uintptr_t page_offset(uintptr_t x) {
52   return x & (page_size() - 1);
53 }
54 
55 // Returns the address of the next page after address 'x', unless 'x' is
56 // itself at the start of a page.
page_end(uintptr_t x)57 inline uintptr_t page_end(uintptr_t x) {
58   return page_start(x + page_size() - 1);
59 }
60