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;}), \ 44 __FILE__ ":" __stringify(__LINE__) ": " \ 45 __stringify(_new) \ 46 " is larger than " \ 47 __stringify(_orig) ); \ 48 _Static_assert(__alignof__(struct{_new;}) <= __alignof__(struct{_orig;}), \ 49 __FILE__ ":" __stringify(__LINE__) ": " \ 50 __stringify(_orig) \ 51 " is not aligned the same as " \ 52 __stringify(_new) ); \ 53 } 54 55 #ifdef __GENKSYMS__ 56 57 #define _ANDROID_KABI_REPLACE(_orig, _new) _orig 58 59 #else 60 61 #define _ANDROID_KABI_REPLACE(_orig, _new) \ 62 union { \ 63 _new; \ 64 struct { \ 65 _orig; \ 66 }; \ 67 __ANDROID_KABI_CHECK_SIZE_ALIGN(_orig, _new); \ 68 } 69 70 #endif /* __GENKSYMS__ */ 71 72 #define _ANDROID_KABI_RESERVE(n) u64 android_kabi_reserved##n 73 74 75 /* 76 * Macros to use _before_ the ABI is frozen 77 */ 78 79 /* 80 * ANDROID_KABI_RESERVE 81 * Reserve some "padding" in a structure for potential future use. 82 * This normally placed at the end of a structure. 83 * number: the "number" of the padding variable in the structure. Start with 84 * 1 and go up. 85 */ 86 #define ANDROID_KABI_RESERVE(number) _ANDROID_KABI_RESERVE(number) 87 88 89 /* 90 * Macros to use _after_ the ABI is frozen 91 */ 92 93 /* 94 * ANDROID_KABI_USE(number, _new) 95 * Use a previous padding entry that was defined with ANDROID_KABI_RESERVE 96 * number: the previous "number" of the padding variable 97 * _new: the variable to use now instead of the padding variable 98 */ 99 #define ANDROID_KABI_USE(number, _new) \ 100 _ANDROID_KABI_REPLACE(_ANDROID_KABI_RESERVE(number), _new) 101 102 /* 103 * ANDROID_KABI_USE2(number, _new1, _new2) 104 * Use a previous padding entry that was defined with ANDROID_KABI_RESERVE for 105 * two new variables that fit into 64 bits. This is good for when you do not 106 * want to "burn" a 64bit padding variable for a smaller variable size if not 107 * needed. 108 */ 109 #define ANDROID_KABI_USE2(number, _new1, _new2) \ 110 _ANDROID_KABI_REPLACE(_ANDROID_KABI_RESERVE(number), struct{ _new1; _new2; }) 111 112 113 #endif /* _ANDROID_KABI_H */ 114