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 */
15 void 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 /*
113 * These macros help objtool understand GCC code flow for unreachable code.
114 * The __COUNTER__ based labels are a hack to make each instance of the macros
115 * unique, to convince GCC not to merge duplicate inline asm statements.
116 */
117 #define __stringify_label(n) #n
118
119 #define __annotate_reachable(c) ({ \
120 asm volatile(__stringify_label(c) ":\n\t" \
121 ".pushsection .discard.reachable\n\t" \
122 ".long " __stringify_label(c) "b - .\n\t" \
123 ".popsection\n\t"); \
124 })
125 #define annotate_reachable() __annotate_reachable(__COUNTER__)
126
127 #define __annotate_unreachable(c) ({ \
128 asm volatile(__stringify_label(c) ":\n\t" \
129 ".pushsection .discard.unreachable\n\t" \
130 ".long " __stringify_label(c) "b - .\n\t" \
131 ".popsection\n\t" : : "i" (c)); \
132 })
133 #define annotate_unreachable() __annotate_unreachable(__COUNTER__)
134
135 /* Annotate a C jump table to allow objtool to follow the code flow */
136 #define __annotate_jump_table __section(".rodata..c_jump_table,\"a\",@progbits #")
137
138 #else /* !CONFIG_OBJTOOL */
139 #define annotate_reachable()
140 #define annotate_unreachable()
141 #define __annotate_jump_table
142 #endif /* CONFIG_OBJTOOL */
143
144 #ifndef unreachable
145 # define unreachable() do { \
146 annotate_unreachable(); \
147 __builtin_unreachable(); \
148 } while (0)
149 #endif
150
151 /*
152 * KENTRY - kernel entry point
153 * This can be used to annotate symbols (functions or data) that are used
154 * without their linker symbol being referenced explicitly. For example,
155 * interrupt vector handlers, or functions in the kernel image that are found
156 * programatically.
157 *
158 * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
159 * are handled in their own way (with KEEP() in linker scripts).
160 *
161 * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
162 * linker script. For example an architecture could KEEP() its entire
163 * boot/exception vector code rather than annotate each function and data.
164 */
165 #ifndef KENTRY
166 # define KENTRY(sym) \
167 extern typeof(sym) sym; \
168 static const unsigned long __kentry_##sym \
169 __used \
170 __attribute__((__section__("___kentry+" #sym))) \
171 = (unsigned long)&sym;
172 #endif
173
174 #ifndef RELOC_HIDE
175 # define RELOC_HIDE(ptr, off) \
176 ({ unsigned long __ptr; \
177 __ptr = (unsigned long) (ptr); \
178 (typeof(ptr)) (__ptr + (off)); })
179 #endif
180
181 #define absolute_pointer(val) RELOC_HIDE((void *)(val), 0)
182
183 #ifndef OPTIMIZER_HIDE_VAR
184 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
185 #define OPTIMIZER_HIDE_VAR(var) \
186 __asm__ ("" : "=r" (var) : "" (var))
187 #endif
188
189 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
190
191 /**
192 * data_race - mark an expression as containing intentional data races
193 *
194 * This data_race() macro is useful for situations in which data races
195 * should be forgiven. One example is diagnostic code that accesses
196 * shared variables but is not a part of the core synchronization design.
197 * For example, if accesses to a given variable are protected by a lock,
198 * except for diagnostic code, then the accesses under the lock should
199 * be plain C-language accesses and those in the diagnostic code should
200 * use data_race(). This way, KCSAN will complain if buggy lockless
201 * accesses to that variable are introduced, even if the buggy accesses
202 * are protected by READ_ONCE() or WRITE_ONCE().
203 *
204 * This macro *does not* affect normal code generation, but is a hint
205 * to tooling that data races here are to be ignored. If the access must
206 * be atomic *and* KCSAN should ignore the access, use both data_race()
207 * and READ_ONCE(), for example, data_race(READ_ONCE(x)).
208 */
209 #define data_race(expr) \
210 ({ \
211 __kcsan_disable_current(); \
212 __auto_type __v = (expr); \
213 __kcsan_enable_current(); \
214 __v; \
215 })
216
217 #endif /* __KERNEL__ */
218
219 /*
220 * Force the compiler to emit 'sym' as a symbol, so that we can reference
221 * it from inline assembler. Necessary in case 'sym' could be inlined
222 * otherwise, or eliminated entirely due to lack of references that are
223 * visible to the compiler.
224 */
225 #define ___ADDRESSABLE(sym, __attrs) \
226 static void * __used __attrs \
227 __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)(uintptr_t)&sym;
228 #define __ADDRESSABLE(sym) \
229 ___ADDRESSABLE(sym, __section(".discard.addressable"))
230
231 /**
232 * offset_to_ptr - convert a relative memory offset to an absolute pointer
233 * @off: the address of the 32-bit offset value
234 */
235 static inline void *offset_to_ptr(const int *off)
236 {
237 return (void *)((unsigned long)off + *off);
238 }
239
240 #endif /* __ASSEMBLY__ */
241
242 /* &a[0] degrades to a pointer: a different type from an array */
243 #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
244
245 /*
246 * This returns a constant expression while determining if an argument is
247 * a constant expression, most importantly without evaluating the argument.
248 * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
249 *
250 * Details:
251 * - sizeof() return an integer constant expression, and does not evaluate
252 * the value of its operand; it only examines the type of its operand.
253 * - The results of comparing two integer constant expressions is also
254 * an integer constant expression.
255 * - The first literal "8" isn't important. It could be any literal value.
256 * - The second literal "8" is to avoid warnings about unaligned pointers;
257 * this could otherwise just be "1".
258 * - (long)(x) is used to avoid warnings about 64-bit types on 32-bit
259 * architectures.
260 * - The C Standard defines "null pointer constant", "(void *)0", as
261 * distinct from other void pointers.
262 * - If (x) is an integer constant expression, then the "* 0l" resolves
263 * it into an integer constant expression of value 0. Since it is cast to
264 * "void *", this makes the second operand a null pointer constant.
265 * - If (x) is not an integer constant expression, then the second operand
266 * resolves to a void pointer (but not a null pointer constant: the value
267 * is not an integer constant 0).
268 * - The conditional operator's third operand, "(int *)8", is an object
269 * pointer (to type "int").
270 * - The behavior (including the return type) of the conditional operator
271 * ("operand1 ? operand2 : operand3") depends on the kind of expressions
272 * given for the second and third operands. This is the central mechanism
273 * of the macro:
274 * - When one operand is a null pointer constant (i.e. when x is an integer
275 * constant expression) and the other is an object pointer (i.e. our
276 * third operand), the conditional operator returns the type of the
277 * object pointer operand (i.e. "int *"). Here, within the sizeof(), we
278 * would then get:
279 * sizeof(*((int *)(...)) == sizeof(int) == 4
280 * - When one operand is a void pointer (i.e. when x is not an integer
281 * constant expression) and the other is an object pointer (i.e. our
282 * third operand), the conditional operator returns a "void *" type.
283 * Here, within the sizeof(), we would then get:
284 * sizeof(*((void *)(...)) == sizeof(void) == 1
285 * - The equality comparison to "sizeof(int)" therefore depends on (x):
286 * sizeof(int) == sizeof(int) (x) was a constant expression
287 * sizeof(int) != sizeof(void) (x) was not a constant expression
288 */
289 #define __is_constexpr(x) \
290 (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
291
292 /*
293 * Whether 'type' is a signed type or an unsigned type. Supports scalar types,
294 * bool and also pointer types.
295 */
296 #define is_signed_type(type) (((type)(-1)) < (__force type)1)
297 #define is_unsigned_type(type) (!is_signed_type(type))
298
299 /*
300 * Useful shorthand for "is this condition known at compile-time?"
301 *
302 * Note that the condition may involve non-constant values,
303 * but the compiler may know enough about the details of the
304 * values to determine that the condition is statically true.
305 */
306 #define statically_true(x) (__builtin_constant_p(x) && (x))
307
308 /*
309 * This is needed in functions which generate the stack canary, see
310 * arch/x86/kernel/smpboot.c::start_secondary() for an example.
311 */
312 #define prevent_tail_call_optimization() mb()
313
314 #include <asm/rwonce.h>
315
316 #endif /* __LINUX_COMPILER_H */
317
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