LXR linux/include/linux/compiler.h

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

#include <linux/compiler_types.h>

#ifndef __ASSEMBLY__

#ifdef __KERNEL__

 /*
  * Note: DISABLE_BRANCH_PROFILING can be used by special lowlevel code
  * to disable branch tracing on a per file basis.
  */
void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 int expect, int is_constant);
#if defined(CONFIG_TRACE_BRANCH_PROFILING) \
 && !defined(DISABLE_BRANCH_PROFILING) && !defined(__CHECKER__)
#define likely_notrace(x) __builtin_expect(!!(x), 1)
#define unlikely_notrace(x) __builtin_expect(!!(x), 0)

#define __branch_check__(x, expect, is_constant) ({ \
 long ______r; \
 static struct ftrace_likely_data \
 __aligned(4) \
 __section("_ftrace_annotated_branch") \
 ______f = { \
 .data.func = __func__, \
 .data.file = __FILE__, \
 .data.line = __LINE__, \
 }; \
 ______r = __builtin_expect(!!(x), expect); \
 ftrace_likely_update(&______f, ______r, \
 expect, is_constant); \
 ______r; \
 })

 /*
  * Using __builtin_constant_p(x) to ignore cases where the return
  * value is always the same. This idea is taken from a similar patch
  * written by Daniel Walker.
  */
# ifndef likely
# define likely(x) (__branch_check__(x, 1, __builtin_constant_p(x)))
# endif
# ifndef unlikely
# define unlikely(x) (__branch_check__(x, 0, __builtin_constant_p(x)))
# endif

#ifdef CONFIG_PROFILE_ALL_BRANCHES
 /*
  * "Define 'is'", Bill Clinton
  * "Define 'if'", Steven Rostedt
  */
#define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )

#define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))

#define __trace_if_value(cond) ({ \
 static struct ftrace_branch_data \
 __aligned(4) \
 __section("_ftrace_branch") \
 __if_trace = { \
 .func = __func__, \
 .file = __FILE__, \
 .line = __LINE__, \
 }; \
 (cond) ? \
 (__if_trace.miss_hit[1]++,1) : \
 (__if_trace.miss_hit[0]++,0); \
})

#endif /* CONFIG_PROFILE_ALL_BRANCHES */

#else
# define likely(x) __builtin_expect(!!(x), 1)
# define unlikely(x) __builtin_expect(!!(x), 0)
# define likely_notrace(x) likely(x)
# define unlikely_notrace(x) unlikely(x)
#endif

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

#ifndef barrier_data
 /*
  * This version is i.e. to prevent dead stores elimination on @ptr
  * where gcc and llvm may behave differently when otherwise using
  * normal barrier(): while gcc behavior gets along with a normal
  * barrier(), llvm needs an explicit input variable to be assumed
  * clobbered. The issue is as follows: while the inline asm might
  * access any memory it wants, the compiler could have fit all of
  * @ptr into memory registers instead, and since @ptr never escaped
  * from that, it proved that the inline asm wasn't touching any of
  * it. This version works well with both compilers, i.e. we're telling
  * the compiler that the inline asm absolutely may see the contents
  * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
  */
# define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
#endif

 /* workaround for GCC PR82365 if needed */
#ifndef barrier_before_unreachable
# define barrier_before_unreachable() do { } while (0)
#endif

 /* Unreachable code */
#ifdef CONFIG_OBJTOOL
 /*
  * These macros help objtool understand GCC code flow for unreachable code.
  * The __COUNTER__ based labels are a hack to make each instance of the macros
  * unique, to convince GCC not to merge duplicate inline asm statements.
  */
#define __stringify_label(n) #n

#define __annotate_unreachable(c) ({ \
 asm volatile(__stringify_label(c) ":\n\t" \
 ".pushsection .discard.unreachable\n\t" \
 ".long " __stringify_label(c) "b - .\n\t" \
 ".popsection\n\t" : : "i" (c)); \
})
#define annotate_unreachable() __annotate_unreachable(__COUNTER__)

 /* Annotate a C jump table to allow objtool to follow the code flow */
#define __annotate_jump_table __section(".rodata..c_jump_table")

#else /* !CONFIG_OBJTOOL */
#define annotate_unreachable()
#define __annotate_jump_table
#endif /* CONFIG_OBJTOOL */

#ifndef unreachable
# define unreachable() do { \
 annotate_unreachable(); \
 __builtin_unreachable(); \
} while (0)
#endif

 /*
  * KENTRY - kernel entry point
  * This can be used to annotate symbols (functions or data) that are used
  * without their linker symbol being referenced explicitly. For example,
  * interrupt vector handlers, or functions in the kernel image that are found
  * programatically.
  *
  * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
  * are handled in their own way (with KEEP() in linker scripts).
  *
  * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
  * linker script. For example an architecture could KEEP() its entire
  * boot/exception vector code rather than annotate each function and data.
  */
#ifndef KENTRY
# define KENTRY(sym) \
 extern typeof(sym) sym; \
 static const unsigned long __kentry_##sym \
 __used \
 __attribute__((__section__("___kentry+" #sym))) \
 = (unsigned long)&sym;
#endif

#ifndef RELOC_HIDE
# define RELOC_HIDE(ptr, off) \
 ({ unsigned long __ptr; \
 __ptr = (unsigned long) (ptr); \
 (typeof(ptr)) (__ptr + (off)); })
#endif

#define absolute_pointer(val) RELOC_HIDE((void *)(val), 0)

#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

#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)

 /**
  * data_race - mark an expression as containing intentional data races
  *
  * This data_race() macro is useful for situations in which data races
  * should be forgiven. One example is diagnostic code that accesses
  * shared variables but is not a part of the core synchronization design.
  *
  * This macro *does not* affect normal code generation, but is a hint
  * to tooling that data races here are to be ignored.
  */
#define data_race(expr) \
({ \
 __unqual_scalar_typeof(({ expr; })) __v = ({ \
 __kcsan_disable_current(); \
 expr; \
 }); \
 __kcsan_enable_current(); \
 __v; \
})

#endif /* __KERNEL__ */

 /*
  * Force the compiler to emit 'sym' as a symbol, so that we can reference
  * it from inline assembler. Necessary in case 'sym' could be inlined
  * otherwise, or eliminated entirely due to lack of references that are
  * visible to the compiler.
  */
#define ___ADDRESSABLE(sym, __attrs) \
 static void * __used __attrs \
 __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)&sym;
#define __ADDRESSABLE(sym) \
 ___ADDRESSABLE(sym, __section(".discard.addressable"))

 /**
  * offset_to_ptr - convert a relative memory offset to an absolute pointer
  * @off: the address of the 32-bit offset value
  */
static inline void *offset_to_ptr(const int *off)
{
 return (void *)((unsigned long)off + *off);
}

#endif /* __ASSEMBLY__ */

 /* &a[0] degrades to a pointer: a different type from an array */
#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))

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

 /*
  * Whether 'type' is a signed type or an unsigned type. Supports scalar types,
  * bool and also pointer types.
  */
#define is_signed_type(type) (((type)(-1)) < (__force type)1)
#define is_unsigned_type(type) (!is_signed_type(type))

 /*
  * This is needed in functions which generate the stack canary, see
  * arch/x86/kernel/smpboot.c::start_secondary() for an example.
  */
#define prevent_tail_call_optimization() mb()

#include <asm/rwonce.h>

#endif /* __LINUX_COMPILER_H */