kernel / tools / include / linux / compiler.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _TOOLS_LINUX_COMPILER_H_
#define _TOOLS_LINUX_COMPILER_H_

#ifndef __ASSEMBLY__

#include <linux/compiler_types.h>

#ifndef __compiletime_error
# define __compiletime_error(message)
#endif

#ifdef __OPTIMIZE__
# define __compiletime_assert(condition, msg, prefix, suffix)		\
	do {								\
		extern void prefix ## suffix(void) __compiletime_error(msg); \
		if (!(condition))					\
			prefix ## suffix();				\
	} while (0)
#else
# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
#endif

#define _compiletime_assert(condition, msg, prefix, suffix) \
	__compiletime_assert(condition, msg, prefix, suffix)

/**
 * compiletime_assert - break build and emit msg if condition is false
 * @condition: a compile-time constant condition to check
 * @msg:       a message to emit if condition is false
 *
 * In tradition of POSIX assert, this macro will break the build if the
 * supplied condition is *false*, emitting the supplied error message if the
 * compiler has support to do so.
 */
#define compiletime_assert(condition, msg) \
	_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)

/* Optimization barrier */
/* The "volatile" is due to gcc bugs */
#define barrier() __asm__ __volatile__("": : :"memory")

#ifndef __always_inline
# define __always_inline	inline __attribute__((always_inline))
#endif

#ifndef __always_unused
#define __always_unused __attribute__((__unused__))
#endif

#ifndef __noreturn
#define __noreturn __attribute__((__noreturn__))
#endif

#ifndef unreachable
#define unreachable() __builtin_unreachable()
#endif

#ifndef noinline
#define noinline
#endif

#ifndef __nocf_check
#define __nocf_check __attribute__((nocf_check))
#endif

#ifndef __naked
#define __naked __attribute__((__naked__))
#endif

/* Are two types/vars the same type (ignoring qualifiers)? */
#ifndef __same_type
# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
#endif

/*
 * This returns a constant expression while determining if an argument is
 * a constant expression, most importantly without evaluating the argument.
 * Glory to Martin Uecker <[e-mail]>
 */
#define __is_constexpr(x) \
	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))

/*
 * Similar to statically_true() but produces a constant expression
 *
 * To be used in conjunction with macros, such as BUILD_BUG_ON_ZERO(),
 * which require their input to be a constant expression and for which
 * statically_true() would otherwise fail.
 *
 * This is a trade-off: const_true() requires all its operands to be
 * compile time constants. Else, it would always returns false even on
 * the most trivial cases like:
 *
 *   true || non_const_var
 *
 * On the opposite, statically_true() is able to fold more complex
 * tautologies and will return true on expressions such as:
 *
 *   !(non_const_var * 8 % 4)
 *
 * For the general case, statically_true() is better.
 */
#define const_true(x) __builtin_choose_expr(__is_constexpr(x), x, false)

#ifdef __ANDROID__
/*
 * FIXME: Big hammer to get rid of tons of:
 *   "warning: always_inline function might not be inlinable"
 *
 * At least on android-ndk-r12/platforms/android-24/arch-arm
 */
#undef __always_inline
#define __always_inline	inline
#endif

#define __user
#define __rcu
#define __read_mostly

#ifndef __attribute_const__
# define __attribute_const__
#endif

#ifndef __maybe_unused
# define __maybe_unused		__attribute__((unused))
#endif

#ifndef __used
# define __used		__attribute__((__unused__))
#endif

#ifndef __packed
# define __packed		__attribute__((__packed__))
#endif

#ifndef __force
# define __force
#endif

#ifndef __weak
# define __weak			__attribute__((weak))
#endif

#ifndef likely
# define likely(x)		__builtin_expect(!!(x), 1)
#endif

#ifndef unlikely
# define unlikely(x)		__builtin_expect(!!(x), 0)
#endif

#include <linux/types.h>

/*
 * Following functions are taken from kernel sources and
 * break aliasing rules in their original form.
 *
 * While kernel is compiled with -fno-strict-aliasing,
 * perf uses -Wstrict-aliasing=3 which makes build fail
 * under gcc 4.4.
 *
 * Using extra __may_alias__ type to allow aliasing
 * in this case.
 */
typedef __u8  __attribute__((__may_alias__))  __u8_alias_t;
typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;

static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
{
	switch (size) {
	case 1: *(__u8_alias_t  *) res = *(volatile __u8_alias_t  *) p; break;
	case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
	case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
	case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
	default:
		barrier();
		__builtin_memcpy((void *)res, (const void *)p, size);
		barrier();
	}
}

static __always_inline void __write_once_size(volatile void *p, void *res, int size)
{
	switch (size) {
	case 1: *(volatile  __u8_alias_t *) p = *(__u8_alias_t  *) res; break;
	case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
	case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
	case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
	default:
		barrier();
		__builtin_memcpy((void *)p, (const void *)res, size);
		barrier();
	}
}

/*
 * Prevent the compiler from merging or refetching reads or writes. The
 * compiler is also forbidden from reordering successive instances of
 * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
 * particular ordering. One way to make the compiler aware of ordering is to
 * put the two invocations of READ_ONCE or WRITE_ONCE in different C
 * statements.
 *
 * These two macros will also work on aggregate data types like structs or
 * unions. If the size of the accessed data type exceeds the word size of
 * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
 * fall back to memcpy and print a compile-time warning.
 *
 * Their two major use cases are: (1) Mediating communication between
 * process-level code and irq/NMI handlers, all running on the same CPU,
 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
 * mutilate accesses that either do not require ordering or that interact
 * with an explicit memory barrier or atomic instruction that provides the
 * required ordering.
 */

#define READ_ONCE(x)					\
({							\
	union { typeof(x) __val; char __c[1]; } __u =	\
		{ .__c = { 0 } };			\
	__read_once_size(&(x), __u.__c, sizeof(x));	\
	__u.__val;					\
})

#define WRITE_ONCE(x, val)				\
({							\
	union { typeof(x) __val; char __c[1]; } __u =	\
		{ .__val = (val) }; 			\
	__write_once_size(&(x), __u.__c, sizeof(x));	\
	__u.__val;					\
})


/* Indirect macros required for expanded argument pasting, eg. __LINE__. */
#define ___PASTE(a, b) a##b
#define __PASTE(a, b) ___PASTE(a, b)

#ifndef OPTIMIZER_HIDE_VAR
/* Make the optimizer believe the variable can be manipulated arbitrarily. */
#define OPTIMIZER_HIDE_VAR(var)						\
	__asm__ ("" : "=r" (var) : "0" (var))
#endif

#ifndef __BUILD_BUG_ON_ZERO_MSG
#if defined(__clang__)
#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)(sizeof(struct { int:(-!!(e)); })))
#else
#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
#endif
#endif

#endif /* __ASSEMBLY__ */

#endif /* _TOOLS_LINUX_COMPILER_H */