compiler.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2#ifndef __LINUX_COMPILER_H
  3#define __LINUX_COMPILER_H
  4
  5#include <linux/compiler_types.h>
  6
  7#ifndef __ASSEMBLY__
  8
  9#ifdef __KERNEL__
 10
 11/*
 12 * Note: DISABLE_BRANCH_PROFILING can be used by special lowlevel code
 13 * to disable branch tracing on a per file basis.
 14 */
 15void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 16			  int expect, int is_constant);
 17#if defined(CONFIG_TRACE_BRANCH_PROFILING) \
 18    && !defined(DISABLE_BRANCH_PROFILING) && !defined(__CHECKER__)
 19#define likely_notrace(x)	__builtin_expect(!!(x), 1)
 20#define unlikely_notrace(x)	__builtin_expect(!!(x), 0)
 21
 22#define __branch_check__(x, expect, is_constant) ({			\
 23			long ______r;					\
 24			static struct ftrace_likely_data		\
 25				__aligned(4)				\
 26				__section("_ftrace_annotated_branch")	\
 27				______f = {				\
 28				.data.func = __func__,			\
 29				.data.file = __FILE__,			\
 30				.data.line = __LINE__,			\
 31			};						\
 32			______r = __builtin_expect(!!(x), expect);	\
 33			ftrace_likely_update(&______f, ______r,		\
 34					     expect, is_constant);	\
 35			______r;					\
 36		})
 37
 38/*
 39 * Using __builtin_constant_p(x) to ignore cases where the return
 40 * value is always the same.  This idea is taken from a similar patch
 41 * written by Daniel Walker.
 42 */
 43# ifndef likely
 44#  define likely(x)	(__branch_check__(x, 1, __builtin_constant_p(x)))
 45# endif
 46# ifndef unlikely
 47#  define unlikely(x)	(__branch_check__(x, 0, __builtin_constant_p(x)))
 48# endif
 49
 50#ifdef CONFIG_PROFILE_ALL_BRANCHES
 51/*
 52 * "Define 'is'", Bill Clinton
 53 * "Define 'if'", Steven Rostedt
 54 */
 55#define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
 56
 57#define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
 58
 59#define __trace_if_value(cond) ({			\
 60	static struct ftrace_branch_data		\
 61		__aligned(4)				\
 62		__section("_ftrace_branch")		\
 63		__if_trace = {				\
 64			.func = __func__,		\
 65			.file = __FILE__,		\
 66			.line = __LINE__,		\
 67		};					\
 68	(cond) ?					\
 69		(__if_trace.miss_hit[1]++,1) :		\
 70		(__if_trace.miss_hit[0]++,0);		\
 71})
 72
 73#endif /* CONFIG_PROFILE_ALL_BRANCHES */
 74
 75#else
 76# define likely(x)	__builtin_expect(!!(x), 1)
 77# define unlikely(x)	__builtin_expect(!!(x), 0)
 78# define likely_notrace(x)	likely(x)
 79# define unlikely_notrace(x)	unlikely(x)
 80#endif
 81
 82/* Optimization barrier */
 83#ifndef barrier
 84/* The "volatile" is due to gcc bugs */
 85# define barrier() __asm__ __volatile__("": : :"memory")
 86#endif
 87
 88#ifndef barrier_data
 89/*
 90 * This version is i.e. to prevent dead stores elimination on @ptr
 91 * where gcc and llvm may behave differently when otherwise using
 92 * normal barrier(): while gcc behavior gets along with a normal
 93 * barrier(), llvm needs an explicit input variable to be assumed
 94 * clobbered. The issue is as follows: while the inline asm might
 95 * access any memory it wants, the compiler could have fit all of
 96 * @ptr into memory registers instead, and since @ptr never escaped
 97 * from that, it proved that the inline asm wasn't touching any of
 98 * it. This version works well with both compilers, i.e. we're telling
 99 * the compiler that the inline asm absolutely may see the contents
100 * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
101 */
102# define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
103#endif
104
105/* workaround for GCC PR82365 if needed */
106#ifndef barrier_before_unreachable
107# define barrier_before_unreachable() do { } while (0)
108#endif
109
110/* Unreachable code */
111#ifdef CONFIG_OBJTOOL
112/* Annotate a C jump table to allow objtool to follow the code flow */
113#define __annotate_jump_table __section(".data.rel.ro.c_jump_table")
114#else /* !CONFIG_OBJTOOL */
115#define __annotate_jump_table
116#endif /* CONFIG_OBJTOOL */
117
118/*
119 * Mark a position in code as unreachable.  This can be used to
120 * suppress control flow warnings after asm blocks that transfer
121 * control elsewhere.
122 */
123#define unreachable() do {		\
124	barrier_before_unreachable();	\
125	__builtin_unreachable();	\
126} while (0)
127
128/*
129 * KENTRY - kernel entry point
130 * This can be used to annotate symbols (functions or data) that are used
131 * without their linker symbol being referenced explicitly. For example,
132 * interrupt vector handlers, or functions in the kernel image that are found
133 * programatically.
134 *
135 * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
136 * are handled in their own way (with KEEP() in linker scripts).
137 *
138 * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
139 * linker script. For example an architecture could KEEP() its entire
140 * boot/exception vector code rather than annotate each function and data.
141 */
142#ifndef KENTRY
143# define KENTRY(sym)						\
144	extern typeof(sym) sym;					\
145	static const unsigned long __kentry_##sym		\
146	__used							\
147	__attribute__((__section__("___kentry+" #sym)))		\
148	= (unsigned long)&sym;
149#endif
150
151#ifndef RELOC_HIDE
152# define RELOC_HIDE(ptr, off)					\
153  ({ unsigned long __ptr;					\
154     __ptr = (unsigned long) (ptr);				\
155    (typeof(ptr)) (__ptr + (off)); })
156#endif
157
158#define absolute_pointer(val)	RELOC_HIDE((void *)(val), 0)
159
160#ifndef OPTIMIZER_HIDE_VAR
161/* Make the optimizer believe the variable can be manipulated arbitrarily. */
162#define OPTIMIZER_HIDE_VAR(var)						\
163	__asm__ ("" : "=r" (var) : "0" (var))
164#endif
165
166/* Format: __UNIQUE_ID_<name>_<__COUNTER__> */
167#define __UNIQUE_ID(name)					\
168	__PASTE(__UNIQUE_ID_,					\
169	__PASTE(name,						\
170	__PASTE(_, __COUNTER__)))
171
172/**
173 * data_race - mark an expression as containing intentional data races
174 *
175 * This data_race() macro is useful for situations in which data races
176 * should be forgiven.  One example is diagnostic code that accesses
177 * shared variables but is not a part of the core synchronization design.
178 * For example, if accesses to a given variable are protected by a lock,
179 * except for diagnostic code, then the accesses under the lock should
180 * be plain C-language accesses and those in the diagnostic code should
181 * use data_race().  This way, KCSAN will complain if buggy lockless
182 * accesses to that variable are introduced, even if the buggy accesses
183 * are protected by READ_ONCE() or WRITE_ONCE().
184 *
185 * This macro *does not* affect normal code generation, but is a hint
186 * to tooling that data races here are to be ignored.  If the access must
187 * be atomic *and* KCSAN should ignore the access, use both data_race()
188 * and READ_ONCE(), for example, data_race(READ_ONCE(x)).
189 */
190#define data_race(expr)							\
191({									\
192	__kcsan_disable_current();					\
193	auto __v = (expr);						\
194	__kcsan_enable_current();					\
195	__v;								\
196})
197
198#ifdef __CHECKER__
199#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) (0)
200#else /* __CHECKER__ */
201#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
202#endif /* __CHECKER__ */
203
204/* &a[0] degrades to a pointer: a different type from an array */
205#define __is_array(a)		(!__same_type((a), &(a)[0]))
206#define __must_be_array(a)	__BUILD_BUG_ON_ZERO_MSG(!__is_array(a), \
207							"must be array")
208
209#define __is_byte_array(a)	(__is_array(a) && sizeof((a)[0]) == 1)
210#define __must_be_byte_array(a)	__BUILD_BUG_ON_ZERO_MSG(!__is_byte_array(a), \
211							"must be byte array")
212
213/*
214 * If the "nonstring" attribute isn't available, we have to return true
215 * so the __must_*() checks pass when "nonstring" isn't supported.
216 */
217#if __has_attribute(__nonstring__) && defined(__annotated)
218#define __is_cstr(a)		(!__annotated(a, nonstring))
219#define __is_noncstr(a)		(__annotated(a, nonstring))
220#else
221#define __is_cstr(a)		(true)
222#define __is_noncstr(a)		(true)
223#endif
224
225/* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */
226#define __must_be_cstr(p) \
227	__BUILD_BUG_ON_ZERO_MSG(!__is_cstr(p), \
228				"must be C-string (NUL-terminated)")
229#define __must_be_noncstr(p) \
230	__BUILD_BUG_ON_ZERO_MSG(!__is_noncstr(p), \
231				"must be non-C-string (not NUL-terminated)")
232
233/*
234 * Use __typeof_unqual__() when available.
235 *
236 * XXX: Remove test for __CHECKER__ once
237 * sparse learns about __typeof_unqual__().
238 */
239#if CC_HAS_TYPEOF_UNQUAL && !defined(__CHECKER__)
240# define USE_TYPEOF_UNQUAL 1
241#endif
242
243/*
244 * Define TYPEOF_UNQUAL() to use __typeof_unqual__() as typeof
245 * operator when available, to return an unqualified type of the exp.
246 */
247#if defined(USE_TYPEOF_UNQUAL)
248# define TYPEOF_UNQUAL(exp) __typeof_unqual__(exp)
249#else
250# define TYPEOF_UNQUAL(exp) __typeof__(exp)
251#endif
252
253#endif /* __KERNEL__ */
254
255#if defined(CONFIG_CFI) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
256/*
257 * Force a reference to the external symbol so the compiler generates
258 * __kcfi_typid.
259 */
260#define KCFI_REFERENCE(sym) __ADDRESSABLE(sym)
261#else
262#define KCFI_REFERENCE(sym)
263#endif
264
265/**
266 * offset_to_ptr - convert a relative memory offset to an absolute pointer
267 * @off:	the address of the 32-bit offset value
268 */
269static inline void *offset_to_ptr(const int *off)
270{
271	return (void *)((unsigned long)off + *off);
272}
273
274#endif /* __ASSEMBLY__ */
275
276/*
277 * Force the compiler to emit 'sym' as a symbol, so that we can reference
278 * it from inline assembler. Necessary in case 'sym' could be inlined
279 * otherwise, or eliminated entirely due to lack of references that are
280 * visible to the compiler.
281 */
282#define ___ADDRESSABLE(sym, __attrs)						\
283	static void * __used __attrs						\
284	__UNIQUE_ID(__PASTE(addressable_, sym)) = (void *)(uintptr_t)&sym;
285
286#define __ADDRESSABLE(sym) \
287	___ADDRESSABLE(sym, __section(".discard.addressable"))
288
289/*
290 * This returns a constant expression while determining if an argument is
291 * a constant expression, most importantly without evaluating the argument.
292 * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
293 *
294 * Details:
295 * - sizeof() return an integer constant expression, and does not evaluate
296 *   the value of its operand; it only examines the type of its operand.
297 * - The results of comparing two integer constant expressions is also
298 *   an integer constant expression.
299 * - The first literal "8" isn't important. It could be any literal value.
300 * - The second literal "8" is to avoid warnings about unaligned pointers;
301 *   this could otherwise just be "1".
302 * - (long)(x) is used to avoid warnings about 64-bit types on 32-bit
303 *   architectures.
304 * - The C Standard defines "null pointer constant", "(void *)0", as
305 *   distinct from other void pointers.
306 * - If (x) is an integer constant expression, then the "* 0l" resolves
307 *   it into an integer constant expression of value 0. Since it is cast to
308 *   "void *", this makes the second operand a null pointer constant.
309 * - If (x) is not an integer constant expression, then the second operand
310 *   resolves to a void pointer (but not a null pointer constant: the value
311 *   is not an integer constant 0).
312 * - The conditional operator's third operand, "(int *)8", is an object
313 *   pointer (to type "int").
314 * - The behavior (including the return type) of the conditional operator
315 *   ("operand1 ? operand2 : operand3") depends on the kind of expressions
316 *   given for the second and third operands. This is the central mechanism
317 *   of the macro:
318 *   - When one operand is a null pointer constant (i.e. when x is an integer
319 *     constant expression) and the other is an object pointer (i.e. our
320 *     third operand), the conditional operator returns the type of the
321 *     object pointer operand (i.e. "int *"). Here, within the sizeof(), we
322 *     would then get:
323 *       sizeof(*((int *)(...))  == sizeof(int)  == 4
324 *   - When one operand is a void pointer (i.e. when x is not an integer
325 *     constant expression) and the other is an object pointer (i.e. our
326 *     third operand), the conditional operator returns a "void *" type.
327 *     Here, within the sizeof(), we would then get:
328 *       sizeof(*((void *)(...)) == sizeof(void) == 1
329 * - The equality comparison to "sizeof(int)" therefore depends on (x):
330 *     sizeof(int) == sizeof(int)     (x) was a constant expression
331 *     sizeof(int) != sizeof(void)    (x) was not a constant expression
332 */
333#define __is_constexpr(x) \
334	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
335
336/*
337 * Whether 'type' is a signed type or an unsigned type. Supports scalar types,
338 * bool and also pointer types.
339 */
340#define is_signed_type(type) (((type)(-1)) < (__force type)1)
341#define is_unsigned_type(type) (!is_signed_type(type))
342
343/*
344 * Useful shorthand for "is this condition known at compile-time?"
345 *
346 * Note that the condition may involve non-constant values,
347 * but the compiler may know enough about the details of the
348 * values to determine that the condition is statically true.
349 */
350#define statically_true(x) (__builtin_constant_p(x) && (x))
351
352/*
353 * Similar to statically_true() but produces a constant expression
354 *
355 * To be used in conjunction with macros, such as BUILD_BUG_ON_ZERO(),
356 * which require their input to be a constant expression and for which
357 * statically_true() would otherwise fail.
358 *
359 * This is a trade-off: const_true() requires all its operands to be
360 * compile time constants. Else, it would always returns false even on
361 * the most trivial cases like:
362 *
363 *   true || non_const_var
364 *
365 * On the opposite, statically_true() is able to fold more complex
366 * tautologies and will return true on expressions such as:
367 *
368 *   !(non_const_var * 8 % 4)
369 *
370 * For the general case, statically_true() is better.
371 */
372#define const_true(x) __builtin_choose_expr(__is_constexpr(x), x, false)
373
374/*
375 * This is needed in functions which generate the stack canary, see
376 * arch/x86/kernel/smpboot.c::start_secondary() for an example.
377 */
378#define prevent_tail_call_optimization()	mb()
379
380#include <asm/rwonce.h>
381
382#endif /* __LINUX_COMPILER_H */