1 /* SPDX-License-Identifier: GPL-2.0-only */ 2 /* 3 * android_kabi.h - Android kernel abi abstraction header 4 * 5 * Copyright (C) 2020 Google, Inc. 6 * 7 * Heavily influenced by rh_kabi.h which came from the RHEL/CENTOS kernel and 8 * was: 9 * Copyright (c) 2014 Don Zickus 10 * Copyright (c) 2015-2018 Jiri Benc 11 * Copyright (c) 2015 Sabrina Dubroca, Hannes Frederic Sowa 12 * Copyright (c) 2016-2018 Prarit Bhargava 13 * Copyright (c) 2017 Paolo Abeni, Larry Woodman 14 * 15 * These macros are to be used to try to help alleviate future kernel abi 16 * changes that will occur as LTS and other kernel patches are merged into the 17 * tree during a period in which the kernel abi is wishing to not be disturbed. 18 * 19 * There are two times these macros should be used: 20 * - Before the kernel abi is "frozen" 21 * Padding can be added to various kernel structures that have in the past 22 * been known to change over time. That will give "room" in the structure 23 * that can then be used when fields are added so that the structure size 24 * will not change. 25 * 26 * - After the kernel abi is "frozen" 27 * If a structure's field is changed to a type that is identical in size to 28 * the previous type, it can be changed with a union macro 29 * If a field is added to a structure, the padding fields can be used to add 30 * the new field in a "safe" way. 31 */ 32 #ifndef _ANDROID_KABI_H 33 #define _ANDROID_KABI_H 34 35 #include <linux/compiler.h> 36 37 /* 38 * Worker macros, don't use these, use the ones without a leading '_' 39 */ 40 41 #define __ANDROID_KABI_CHECK_SIZE_ALIGN(_orig, _new) \ 42 union { \ 43 _Static_assert(sizeof(struct { _new; }) <= sizeof(struct { _orig; }), __FILE__ \ 44 ":" __stringify(__LINE__) ": " __stringify(_new) " is larger than " __stringify(_orig)); \ 45 _Static_assert( \ 46 __alignof__(struct { _new; }) <= __alignof__(struct { _orig; }), __FILE__ \ 47 ":" __stringify(__LINE__) ": " __stringify(_orig) " is not aligned the same as " __stringify(_new)); \ 48 } 49 50 #ifdef __GENKSYMS__ 51 52 #define _ANDROID_KABI_REPLACE(_orig, _new) _orig 53 54 #else 55 56 #define _ANDROID_KABI_REPLACE(_orig, _new) \ 57 union { \ 58 _new; \ 59 struct { \ 60 _orig; \ 61 } __UNIQUE_ID(android_kabi_hide); \ 62 __ANDROID_KABI_CHECK_SIZE_ALIGN(_orig, _new); \ 63 } 64 65 #endif /* __GENKSYMS__ */ 66 67 #define _ANDROID_KABI_RESERVE(n) u64 android_kabi_reserved##n 68 69 /* 70 * Macros to use _before_ the ABI is frozen 71 */ 72 73 /* 74 * ANDROID_KABI_RESERVE 75 * Reserve some "padding" in a structure for potential future use. 76 * This normally placed at the end of a structure. 77 * number: the "number" of the padding variable in the structure. Start with 78 * 1 and go up. 79 */ 80 #define ANDROID_KABI_RESERVE(number) _ANDROID_KABI_RESERVE(number) 81 82 /* 83 * Macros to use _after_ the ABI is frozen 84 */ 85 86 /* 87 * ANDROID_KABI_USE(number, _new) 88 * Use a previous padding entry that was defined with ANDROID_KABI_RESERVE 89 * number: the previous "number" of the padding variable 90 * _new: the variable to use now instead of the padding variable 91 */ 92 #define ANDROID_KABI_USE(number, _new) _ANDROID_KABI_REPLACE(_ANDROID_KABI_RESERVE(number), _new) 93 94 /* 95 * ANDROID_KABI_USE2(number, _new1, _new2) 96 * Use a previous padding entry that was defined with ANDROID_KABI_RESERVE for 97 * two new variables that fit into 64 bits. This is good for when you do not 98 * want to "burn" a 64bit padding variable for a smaller variable size if not 99 * needed. 100 */ 101 #define ANDROID_KABI_USE2(number, _new1, _new2) \ 102 _ANDROID_KABI_REPLACE( \ 103 _ANDROID_KABI_RESERVE(number), struct { \ 104 _new1; \ 105 _new2; \ 106 }) 107 108 #endif /* _ANDROID_KABI_H */ 109