1 /* 2 * Copyright (C) 2008 The Android Open Source Project 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in 12 * the documentation and/or other materials provided with the 13 * distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS 22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #pragma once 30 31 #include <stdatomic.h> 32 #include <stdint.h> 33 #include <sys/system_properties.h> 34 35 #include "private/bionic_macros.h" 36 37 // The C11 standard doesn't allow atomic loads from const fields, 38 // though C++11 does. Fudge it until standards get straightened out. 39 static inline uint_least32_t load_const_atomic(const atomic_uint_least32_t* s, memory_order mo) { 40 atomic_uint_least32_t* non_const_s = const_cast<atomic_uint_least32_t*>(s); 41 return atomic_load_explicit(non_const_s, mo); 42 } 43 44 struct prop_info { 45 // Read only properties will not set anything but the bottom most bit of serial and the top byte. 46 // We borrow the 2nd from the top byte for extra flags, and use the bottom most bit of that for 47 // our first user, kLongFlag. 48 constexpr static uint32_t kLongFlag = 1 << 16; 49 50 // The error message fits in part of a union with the previous 92 char property value so there 51 // must be room left over after the error message for the offset to the new longer property value 52 // and future expansion fields if needed. Note that this value cannot ever increase. The offset 53 // to the new longer property value appears immediately after it, so an increase of this size will 54 // break compatibility. 55 constexpr static size_t kLongLegacyErrorBufferSize = 56; 56 57 public: 58 atomic_uint_least32_t serial; 59 // we need to keep this buffer around because the property 60 // value can be modified whereas name is constant. 61 union { 62 char value[PROP_VALUE_MAX]; 63 struct { 64 char error_message[kLongLegacyErrorBufferSize]; 65 uint32_t offset; 66 } long_property; 67 }; 68 char name[0]; 69 70 bool is_long() const { 71 return (load_const_atomic(&serial, memory_order_relaxed) & kLongFlag) != 0; 72 } 73 74 const char* long_value() const { 75 // We can't store pointers here since this is shared memory that will have different absolute 76 // pointers in different processes. We don't have data_ from prop_area, but since we know 77 // `this` is data_ + some offset and long_value is data_ + some other offset, we calculate the 78 // offset from `this` to long_value and store it as long_property.offset. 79 return reinterpret_cast<const char*>(this) + long_property.offset; 80 } 81 82 prop_info(const char* name, uint32_t namelen, const char* value, uint32_t valuelen); 83 prop_info(const char* name, uint32_t namelen, uint32_t long_offset); 84 85 private: 86 DISALLOW_IMPLICIT_CONSTRUCTORS(prop_info); 87 }; 88 89 static_assert(sizeof(prop_info) == 96, "sizeof struct prop_info must be 96 bytes"); 90
