android_kabi.h
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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* android_kabi.h - Android kernel abi abstraction header
*
* Copyright (C) 2020 Google, Inc.
*
* Heavily influenced by rh_kabi.h which came from the RHEL/CENTOS kernel and
* was:
* Copyright (c) 2014 Don Zickus
* Copyright (c) 2015-2018 Jiri Benc
* Copyright (c) 2015 Sabrina Dubroca, Hannes Frederic Sowa
* Copyright (c) 2016-2018 Prarit Bhargava
* Copyright (c) 2017 Paolo Abeni, Larry Woodman
*
* These macros are to be used to try to help alleviate future kernel abi
* changes that will occur as LTS and other kernel patches are merged into the
* tree during a period in which the kernel abi is wishing to not be disturbed.
*
* There are two times these macros should be used:
* - Before the kernel abi is "frozen"
* Padding can be added to various kernel structures that have in the past
* been known to change over time. That will give "room" in the structure
* that can then be used when fields are added so that the structure size
* will not change.
*
* - After the kernel abi is "frozen"
* If a structure's field is changed to a type that is identical in size to
* the previous type, it can be changed with a union macro
* If a field is added to a structure, the padding fields can be used to add
* the new field in a "safe" way.
*/
#ifndef _ANDROID_KABI_H
#define _ANDROID_KABI_H
#include <linux/compiler.h>
/*
* Worker macros, don't use these, use the ones without a leading '_'
*/
#define __ANDROID_KABI_CHECK_SIZE_ALIGN(_orig, _new) \
union { \
_Static_assert(sizeof(struct{_new;}) <= sizeof(struct{_orig;}), \
__FILE__ ":" __stringify(__LINE__) ": " \
__stringify(_new) \
" is larger than " \
__stringify(_orig) ); \
_Static_assert(__alignof__(struct{_new;}) <= __alignof__(struct{_orig;}), \
__FILE__ ":" __stringify(__LINE__) ": " \
__stringify(_orig) \
" is not aligned the same as " \
__stringify(_new) ); \
}
#ifdef __GENKSYMS__
#define _ANDROID_KABI_REPLACE(_orig, _new) _orig
#else
#define _ANDROID_KABI_REPLACE(_orig, _new) \
union { \
_new; \
struct { \
_orig; \
} __UNIQUE_ID(android_kabi_hide); \
__ANDROID_KABI_CHECK_SIZE_ALIGN(_orig, _new); \
}
#endif /* __GENKSYMS__ */
#define _ANDROID_KABI_RESERVE(n) u64 android_kabi_reserved##n
/*
* Macros to use _before_ the ABI is frozen
*/
/*
* ANDROID_KABI_RESERVE
* Reserve some "padding" in a structure for potential future use.
* This normally placed at the end of a structure.
* number: the "number" of the padding variable in the structure. Start with
* 1 and go up.
*/
#define ANDROID_KABI_RESERVE(number) _ANDROID_KABI_RESERVE(number)
/*
* Macros to use _after_ the ABI is frozen
*/
/*
* ANDROID_KABI_USE(number, _new)
* Use a previous padding entry that was defined with ANDROID_KABI_RESERVE
* number: the previous "number" of the padding variable
* _new: the variable to use now instead of the padding variable
*/
#define ANDROID_KABI_USE(number, _new) \
_ANDROID_KABI_REPLACE(_ANDROID_KABI_RESERVE(number), _new)
/*
* ANDROID_KABI_USE2(number, _new1, _new2)
* Use a previous padding entry that was defined with ANDROID_KABI_RESERVE for
* two new variables that fit into 64 bits. This is good for when you do not
* want to "burn" a 64bit padding variable for a smaller variable size if not
* needed.
*/
#define ANDROID_KABI_USE2(number, _new1, _new2) \
_ANDROID_KABI_REPLACE(_ANDROID_KABI_RESERVE(number), struct{ _new1; _new2; })
#endif /* _ANDROID_KABI_H */