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1da177e4 LT |
1 | #ifndef __LINUX_COMPILER_H |
2 | #define __LINUX_COMPILER_H | |
3 | ||
4 | #ifndef __ASSEMBLY__ | |
5 | ||
6 | #ifdef __CHECKER__ | |
7 | # define __user __attribute__((noderef, address_space(1))) | |
e0fdb0e0 | 8 | # define __kernel __attribute__((address_space(0))) |
1da177e4 LT |
9 | # define __safe __attribute__((safe)) |
10 | # define __force __attribute__((force)) | |
11 | # define __nocast __attribute__((nocast)) | |
12 | # define __iomem __attribute__((noderef, address_space(2))) | |
8529091e | 13 | # define __must_hold(x) __attribute__((context(x,1,1))) |
c902e0a0 JT |
14 | # define __acquires(x) __attribute__((context(x,0,1))) |
15 | # define __releases(x) __attribute__((context(x,1,0))) | |
16 | # define __acquire(x) __context__(x,1) | |
17 | # define __release(x) __context__(x,-1) | |
dcc8e559 | 18 | # define __cond_lock(x,c) ((c) ? ({ __acquire(x); 1; }) : 0) |
e0fdb0e0 | 19 | # define __percpu __attribute__((noderef, address_space(3))) |
ca5ecddf PM |
20 | #ifdef CONFIG_SPARSE_RCU_POINTER |
21 | # define __rcu __attribute__((noderef, address_space(4))) | |
ad315455 | 22 | #else /* CONFIG_SPARSE_RCU_POINTER */ |
71d1d5c7 | 23 | # define __rcu |
ad315455 BF |
24 | #endif /* CONFIG_SPARSE_RCU_POINTER */ |
25 | # define __private __attribute__((noderef)) | |
c47ffe3d AV |
26 | extern void __chk_user_ptr(const volatile void __user *); |
27 | extern void __chk_io_ptr(const volatile void __iomem *); | |
ad315455 BF |
28 | # define ACCESS_PRIVATE(p, member) (*((typeof((p)->member) __force *) &(p)->member)) |
29 | #else /* __CHECKER__ */ | |
1da177e4 LT |
30 | # define __user |
31 | # define __kernel | |
32 | # define __safe | |
33 | # define __force | |
34 | # define __nocast | |
35 | # define __iomem | |
36 | # define __chk_user_ptr(x) (void)0 | |
37 | # define __chk_io_ptr(x) (void)0 | |
38 | # define __builtin_warning(x, y...) (1) | |
8529091e | 39 | # define __must_hold(x) |
1da177e4 LT |
40 | # define __acquires(x) |
41 | # define __releases(x) | |
42 | # define __acquire(x) (void)0 | |
43 | # define __release(x) (void)0 | |
dcc8e559 | 44 | # define __cond_lock(x,c) (c) |
e0fdb0e0 | 45 | # define __percpu |
71d1d5c7 | 46 | # define __rcu |
ad315455 BF |
47 | # define __private |
48 | # define ACCESS_PRIVATE(p, member) ((p)->member) | |
49 | #endif /* __CHECKER__ */ | |
1da177e4 | 50 | |
6f33d587 RR |
51 | /* Indirect macros required for expanded argument pasting, eg. __LINE__. */ |
52 | #define ___PASTE(a,b) a##b | |
53 | #define __PASTE(a,b) ___PASTE(a,b) | |
54 | ||
1da177e4 LT |
55 | #ifdef __KERNEL__ |
56 | ||
f153b821 LT |
57 | #ifdef __GNUC__ |
58 | #include <linux/compiler-gcc.h> | |
1da177e4 LT |
59 | #endif |
60 | ||
0c5a69f4 | 61 | #if defined(CC_USING_HOTPATCH) && !defined(__CHECKER__) |
61f55214 HC |
62 | #define notrace __attribute__((hotpatch(0,0))) |
63 | #else | |
28614889 | 64 | #define notrace __attribute__((no_instrument_function)) |
61f55214 | 65 | #endif |
28614889 | 66 | |
1da177e4 LT |
67 | /* Intel compiler defines __GNUC__. So we will overwrite implementations |
68 | * coming from above header files here | |
69 | */ | |
70 | #ifdef __INTEL_COMPILER | |
71 | # include <linux/compiler-intel.h> | |
72 | #endif | |
73 | ||
565cbdc2 MC |
74 | /* Clang compiler defines __GNUC__. So we will overwrite implementations |
75 | * coming from above header files here | |
76 | */ | |
77 | #ifdef __clang__ | |
78 | #include <linux/compiler-clang.h> | |
79 | #endif | |
80 | ||
1da177e4 LT |
81 | /* |
82 | * Generic compiler-dependent macros required for kernel | |
83 | * build go below this comment. Actual compiler/compiler version | |
84 | * specific implementations come from the above header files | |
85 | */ | |
86 | ||
2ed84eeb | 87 | struct ftrace_branch_data { |
1f0d69a9 SR |
88 | const char *func; |
89 | const char *file; | |
90 | unsigned line; | |
2bcd521a SR |
91 | union { |
92 | struct { | |
93 | unsigned long correct; | |
94 | unsigned long incorrect; | |
95 | }; | |
96 | struct { | |
97 | unsigned long miss; | |
98 | unsigned long hit; | |
99 | }; | |
97e7e4f3 | 100 | unsigned long miss_hit[2]; |
2bcd521a | 101 | }; |
1f0d69a9 | 102 | }; |
2ed84eeb SR |
103 | |
104 | /* | |
105 | * Note: DISABLE_BRANCH_PROFILING can be used by special lowlevel code | |
106 | * to disable branch tracing on a per file basis. | |
107 | */ | |
d9ad8bc0 BVA |
108 | #if defined(CONFIG_TRACE_BRANCH_PROFILING) \ |
109 | && !defined(DISABLE_BRANCH_PROFILING) && !defined(__CHECKER__) | |
2ed84eeb | 110 | void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); |
1f0d69a9 SR |
111 | |
112 | #define likely_notrace(x) __builtin_expect(!!(x), 1) | |
113 | #define unlikely_notrace(x) __builtin_expect(!!(x), 0) | |
114 | ||
45b79749 | 115 | #define __branch_check__(x, expect) ({ \ |
1f0d69a9 | 116 | int ______r; \ |
2ed84eeb | 117 | static struct ftrace_branch_data \ |
1f0d69a9 | 118 | __attribute__((__aligned__(4))) \ |
45b79749 | 119 | __attribute__((section("_ftrace_annotated_branch"))) \ |
1f0d69a9 SR |
120 | ______f = { \ |
121 | .func = __func__, \ | |
122 | .file = __FILE__, \ | |
123 | .line = __LINE__, \ | |
124 | }; \ | |
1f0d69a9 | 125 | ______r = likely_notrace(x); \ |
45b79749 | 126 | ftrace_likely_update(&______f, ______r, expect); \ |
1f0d69a9 SR |
127 | ______r; \ |
128 | }) | |
129 | ||
130 | /* | |
131 | * Using __builtin_constant_p(x) to ignore cases where the return | |
132 | * value is always the same. This idea is taken from a similar patch | |
133 | * written by Daniel Walker. | |
134 | */ | |
135 | # ifndef likely | |
45b79749 | 136 | # define likely(x) (__builtin_constant_p(x) ? !!(x) : __branch_check__(x, 1)) |
1f0d69a9 SR |
137 | # endif |
138 | # ifndef unlikely | |
45b79749 | 139 | # define unlikely(x) (__builtin_constant_p(x) ? !!(x) : __branch_check__(x, 0)) |
1f0d69a9 | 140 | # endif |
2bcd521a SR |
141 | |
142 | #ifdef CONFIG_PROFILE_ALL_BRANCHES | |
143 | /* | |
144 | * "Define 'is'", Bill Clinton | |
145 | * "Define 'if'", Steven Rostedt | |
146 | */ | |
ab3c9c68 LT |
147 | #define if(cond, ...) __trace_if( (cond , ## __VA_ARGS__) ) |
148 | #define __trace_if(cond) \ | |
b33c8ff4 | 149 | if (__builtin_constant_p(!!(cond)) ? !!(cond) : \ |
2bcd521a SR |
150 | ({ \ |
151 | int ______r; \ | |
152 | static struct ftrace_branch_data \ | |
153 | __attribute__((__aligned__(4))) \ | |
154 | __attribute__((section("_ftrace_branch"))) \ | |
155 | ______f = { \ | |
156 | .func = __func__, \ | |
157 | .file = __FILE__, \ | |
158 | .line = __LINE__, \ | |
159 | }; \ | |
160 | ______r = !!(cond); \ | |
97e7e4f3 | 161 | ______f.miss_hit[______r]++; \ |
2bcd521a SR |
162 | ______r; \ |
163 | })) | |
164 | #endif /* CONFIG_PROFILE_ALL_BRANCHES */ | |
165 | ||
1f0d69a9 SR |
166 | #else |
167 | # define likely(x) __builtin_expect(!!(x), 1) | |
168 | # define unlikely(x) __builtin_expect(!!(x), 0) | |
169 | #endif | |
1da177e4 LT |
170 | |
171 | /* Optimization barrier */ | |
172 | #ifndef barrier | |
173 | # define barrier() __memory_barrier() | |
174 | #endif | |
175 | ||
7829fb09 DB |
176 | #ifndef barrier_data |
177 | # define barrier_data(ptr) barrier() | |
178 | #endif | |
179 | ||
38938c87 DD |
180 | /* Unreachable code */ |
181 | #ifndef unreachable | |
182 | # define unreachable() do { } while (1) | |
183 | #endif | |
184 | ||
1da177e4 LT |
185 | #ifndef RELOC_HIDE |
186 | # define RELOC_HIDE(ptr, off) \ | |
187 | ({ unsigned long __ptr; \ | |
188 | __ptr = (unsigned long) (ptr); \ | |
189 | (typeof(ptr)) (__ptr + (off)); }) | |
190 | #endif | |
191 | ||
fe8c8a12 CEB |
192 | #ifndef OPTIMIZER_HIDE_VAR |
193 | #define OPTIMIZER_HIDE_VAR(var) barrier() | |
194 | #endif | |
195 | ||
6f33d587 RR |
196 | /* Not-quite-unique ID. */ |
197 | #ifndef __UNIQUE_ID | |
198 | # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__) | |
199 | #endif | |
200 | ||
230fa253 CB |
201 | #include <uapi/linux/types.h> |
202 | ||
d976441f AR |
203 | #define __READ_ONCE_SIZE \ |
204 | ({ \ | |
205 | switch (size) { \ | |
206 | case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \ | |
207 | case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \ | |
208 | case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \ | |
209 | case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \ | |
210 | default: \ | |
211 | barrier(); \ | |
212 | __builtin_memcpy((void *)res, (const void *)p, size); \ | |
213 | barrier(); \ | |
214 | } \ | |
215 | }) | |
216 | ||
217 | static __always_inline | |
218 | void __read_once_size(const volatile void *p, void *res, int size) | |
230fa253 | 219 | { |
d976441f AR |
220 | __READ_ONCE_SIZE; |
221 | } | |
222 | ||
223 | #ifdef CONFIG_KASAN | |
224 | /* | |
225 | * This function is not 'inline' because __no_sanitize_address confilcts | |
226 | * with inlining. Attempt to inline it may cause a build failure. | |
227 | * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368 | |
228 | * '__maybe_unused' allows us to avoid defined-but-not-used warnings. | |
229 | */ | |
230 | static __no_sanitize_address __maybe_unused | |
231 | void __read_once_size_nocheck(const volatile void *p, void *res, int size) | |
232 | { | |
233 | __READ_ONCE_SIZE; | |
234 | } | |
235 | #else | |
236 | static __always_inline | |
237 | void __read_once_size_nocheck(const volatile void *p, void *res, int size) | |
238 | { | |
239 | __READ_ONCE_SIZE; | |
230fa253 | 240 | } |
d976441f | 241 | #endif |
230fa253 | 242 | |
43239cbe | 243 | static __always_inline void __write_once_size(volatile void *p, void *res, int size) |
230fa253 CB |
244 | { |
245 | switch (size) { | |
246 | case 1: *(volatile __u8 *)p = *(__u8 *)res; break; | |
247 | case 2: *(volatile __u16 *)p = *(__u16 *)res; break; | |
248 | case 4: *(volatile __u32 *)p = *(__u32 *)res; break; | |
230fa253 | 249 | case 8: *(volatile __u64 *)p = *(__u64 *)res; break; |
230fa253 CB |
250 | default: |
251 | barrier(); | |
252 | __builtin_memcpy((void *)p, (const void *)res, size); | |
230fa253 CB |
253 | barrier(); |
254 | } | |
255 | } | |
256 | ||
257 | /* | |
258 | * Prevent the compiler from merging or refetching reads or writes. The | |
259 | * compiler is also forbidden from reordering successive instances of | |
43239cbe | 260 | * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the |
230fa253 CB |
261 | * compiler is aware of some particular ordering. One way to make the |
262 | * compiler aware of ordering is to put the two invocations of READ_ONCE, | |
43239cbe | 263 | * WRITE_ONCE or ACCESS_ONCE() in different C statements. |
230fa253 CB |
264 | * |
265 | * In contrast to ACCESS_ONCE these two macros will also work on aggregate | |
266 | * data types like structs or unions. If the size of the accessed data | |
267 | * type exceeds the word size of the machine (e.g., 32 bits or 64 bits) | |
fed0764f KRW |
268 | * READ_ONCE() and WRITE_ONCE() will fall back to memcpy(). There's at |
269 | * least two memcpy()s: one for the __builtin_memcpy() and then one for | |
270 | * the macro doing the copy of variable - '__u' allocated on the stack. | |
230fa253 CB |
271 | * |
272 | * Their two major use cases are: (1) Mediating communication between | |
273 | * process-level code and irq/NMI handlers, all running on the same CPU, | |
274 | * and (2) Ensuring that the compiler does not fold, spindle, or otherwise | |
275 | * mutilate accesses that either do not require ordering or that interact | |
276 | * with an explicit memory barrier or atomic instruction that provides the | |
277 | * required ordering. | |
278 | */ | |
279 | ||
d976441f AR |
280 | #define __READ_ONCE(x, check) \ |
281 | ({ \ | |
282 | union { typeof(x) __val; char __c[1]; } __u; \ | |
283 | if (check) \ | |
284 | __read_once_size(&(x), __u.__c, sizeof(x)); \ | |
285 | else \ | |
286 | __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \ | |
287 | __u.__val; \ | |
288 | }) | |
289 | #define READ_ONCE(x) __READ_ONCE(x, 1) | |
290 | ||
291 | /* | |
292 | * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need | |
293 | * to hide memory access from KASAN. | |
294 | */ | |
295 | #define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0) | |
230fa253 | 296 | |
43239cbe | 297 | #define WRITE_ONCE(x, val) \ |
ba33034f CB |
298 | ({ \ |
299 | union { typeof(x) __val; char __c[1]; } __u = \ | |
300 | { .__val = (__force typeof(x)) (val) }; \ | |
301 | __write_once_size(&(x), __u.__c, sizeof(x)); \ | |
302 | __u.__val; \ | |
303 | }) | |
230fa253 | 304 | |
1da177e4 LT |
305 | #endif /* __KERNEL__ */ |
306 | ||
307 | #endif /* __ASSEMBLY__ */ | |
308 | ||
4f79c3ff | 309 | #ifdef __KERNEL__ |
1da177e4 LT |
310 | /* |
311 | * Allow us to mark functions as 'deprecated' and have gcc emit a nice | |
312 | * warning for each use, in hopes of speeding the functions removal. | |
313 | * Usage is: | |
314 | * int __deprecated foo(void) | |
315 | */ | |
316 | #ifndef __deprecated | |
317 | # define __deprecated /* unimplemented */ | |
318 | #endif | |
319 | ||
512345be PM |
320 | #ifdef MODULE |
321 | #define __deprecated_for_modules __deprecated | |
322 | #else | |
323 | #define __deprecated_for_modules | |
324 | #endif | |
325 | ||
1da177e4 LT |
326 | #ifndef __must_check |
327 | #define __must_check | |
328 | #endif | |
329 | ||
cebc04ba AM |
330 | #ifndef CONFIG_ENABLE_MUST_CHECK |
331 | #undef __must_check | |
332 | #define __must_check | |
333 | #endif | |
de488443 JG |
334 | #ifndef CONFIG_ENABLE_WARN_DEPRECATED |
335 | #undef __deprecated | |
336 | #undef __deprecated_for_modules | |
337 | #define __deprecated | |
338 | #define __deprecated_for_modules | |
339 | #endif | |
cebc04ba | 340 | |
d64e85d3 RV |
341 | #ifndef __malloc |
342 | #define __malloc | |
343 | #endif | |
344 | ||
1da177e4 LT |
345 | /* |
346 | * Allow us to avoid 'defined but not used' warnings on functions and data, | |
347 | * as well as force them to be emitted to the assembly file. | |
348 | * | |
0d7ebbbc DR |
349 | * As of gcc 3.4, static functions that are not marked with attribute((used)) |
350 | * may be elided from the assembly file. As of gcc 3.4, static data not so | |
1da177e4 LT |
351 | * marked will not be elided, but this may change in a future gcc version. |
352 | * | |
0d7ebbbc DR |
353 | * NOTE: Because distributions shipped with a backported unit-at-a-time |
354 | * compiler in gcc 3.3, we must define __used to be __attribute__((used)) | |
355 | * for gcc >=3.3 instead of 3.4. | |
356 | * | |
1da177e4 LT |
357 | * In prior versions of gcc, such functions and data would be emitted, but |
358 | * would be warned about except with attribute((unused)). | |
0d7ebbbc DR |
359 | * |
360 | * Mark functions that are referenced only in inline assembly as __used so | |
361 | * the code is emitted even though it appears to be unreferenced. | |
1da177e4 | 362 | */ |
0d7ebbbc DR |
363 | #ifndef __used |
364 | # define __used /* unimplemented */ | |
365 | #endif | |
366 | ||
367 | #ifndef __maybe_unused | |
368 | # define __maybe_unused /* unimplemented */ | |
1da177e4 LT |
369 | #endif |
370 | ||
7b2a3513 LZ |
371 | #ifndef __always_unused |
372 | # define __always_unused /* unimplemented */ | |
373 | #endif | |
374 | ||
423bc7b2 DW |
375 | #ifndef noinline |
376 | #define noinline | |
377 | #endif | |
378 | ||
735c4fb9 AM |
379 | /* |
380 | * Rather then using noinline to prevent stack consumption, use | |
e6be0c9e | 381 | * noinline_for_stack instead. For documentation reasons. |
735c4fb9 AM |
382 | */ |
383 | #define noinline_for_stack noinline | |
384 | ||
423bc7b2 DW |
385 | #ifndef __always_inline |
386 | #define __always_inline inline | |
387 | #endif | |
388 | ||
389 | #endif /* __KERNEL__ */ | |
390 | ||
1da177e4 LT |
391 | /* |
392 | * From the GCC manual: | |
393 | * | |
394 | * Many functions do not examine any values except their arguments, | |
395 | * and have no effects except the return value. Basically this is | |
396 | * just slightly more strict class than the `pure' attribute above, | |
397 | * since function is not allowed to read global memory. | |
398 | * | |
399 | * Note that a function that has pointer arguments and examines the | |
400 | * data pointed to must _not_ be declared `const'. Likewise, a | |
401 | * function that calls a non-`const' function usually must not be | |
402 | * `const'. It does not make sense for a `const' function to return | |
403 | * `void'. | |
404 | */ | |
405 | #ifndef __attribute_const__ | |
406 | # define __attribute_const__ /* unimplemented */ | |
407 | #endif | |
408 | ||
a586df06 AK |
409 | /* |
410 | * Tell gcc if a function is cold. The compiler will assume any path | |
411 | * directly leading to the call is unlikely. | |
412 | */ | |
413 | ||
414 | #ifndef __cold | |
415 | #define __cold | |
416 | #endif | |
417 | ||
f3fe866d SR |
418 | /* Simple shorthand for a section definition */ |
419 | #ifndef __section | |
420 | # define __section(S) __attribute__ ((__section__(#S))) | |
421 | #endif | |
422 | ||
9a858dc7 AK |
423 | #ifndef __visible |
424 | #define __visible | |
425 | #endif | |
426 | ||
a744fd17 RV |
427 | /* |
428 | * Assume alignment of return value. | |
429 | */ | |
430 | #ifndef __assume_aligned | |
431 | #define __assume_aligned(a, ...) | |
432 | #endif | |
433 | ||
434 | ||
d2c123c2 RR |
435 | /* Are two types/vars the same type (ignoring qualifiers)? */ |
436 | #ifndef __same_type | |
437 | # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b)) | |
438 | #endif | |
439 | ||
47933ad4 PZ |
440 | /* Is this type a native word size -- useful for atomic operations */ |
441 | #ifndef __native_word | |
536fa402 | 442 | # define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long)) |
47933ad4 PZ |
443 | #endif |
444 | ||
9f0cf4ad AV |
445 | /* Compile time object size, -1 for unknown */ |
446 | #ifndef __compiletime_object_size | |
447 | # define __compiletime_object_size(obj) -1 | |
448 | #endif | |
4a312769 AV |
449 | #ifndef __compiletime_warning |
450 | # define __compiletime_warning(message) | |
451 | #endif | |
63312b6a AV |
452 | #ifndef __compiletime_error |
453 | # define __compiletime_error(message) | |
2c0d259e JH |
454 | /* |
455 | * Sparse complains of variable sized arrays due to the temporary variable in | |
456 | * __compiletime_assert. Unfortunately we can't just expand it out to make | |
457 | * sparse see a constant array size without breaking compiletime_assert on old | |
458 | * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether. | |
459 | */ | |
460 | # ifndef __CHECKER__ | |
461 | # define __compiletime_error_fallback(condition) \ | |
9a8ab1c3 | 462 | do { ((void)sizeof(char[1 - 2 * condition])); } while (0) |
2c0d259e JH |
463 | # endif |
464 | #endif | |
465 | #ifndef __compiletime_error_fallback | |
c361d3e5 | 466 | # define __compiletime_error_fallback(condition) do { } while (0) |
63312b6a | 467 | #endif |
c361d3e5 | 468 | |
9a8ab1c3 DS |
469 | #define __compiletime_assert(condition, msg, prefix, suffix) \ |
470 | do { \ | |
471 | bool __cond = !(condition); \ | |
472 | extern void prefix ## suffix(void) __compiletime_error(msg); \ | |
473 | if (__cond) \ | |
474 | prefix ## suffix(); \ | |
475 | __compiletime_error_fallback(__cond); \ | |
476 | } while (0) | |
477 | ||
478 | #define _compiletime_assert(condition, msg, prefix, suffix) \ | |
479 | __compiletime_assert(condition, msg, prefix, suffix) | |
480 | ||
481 | /** | |
482 | * compiletime_assert - break build and emit msg if condition is false | |
483 | * @condition: a compile-time constant condition to check | |
484 | * @msg: a message to emit if condition is false | |
485 | * | |
486 | * In tradition of POSIX assert, this macro will break the build if the | |
487 | * supplied condition is *false*, emitting the supplied error message if the | |
488 | * compiler has support to do so. | |
489 | */ | |
490 | #define compiletime_assert(condition, msg) \ | |
491 | _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) | |
492 | ||
47933ad4 PZ |
493 | #define compiletime_assert_atomic_type(t) \ |
494 | compiletime_assert(__native_word(t), \ | |
495 | "Need native word sized stores/loads for atomicity.") | |
496 | ||
9c3cdc1f LT |
497 | /* |
498 | * Prevent the compiler from merging or refetching accesses. The compiler | |
499 | * is also forbidden from reordering successive instances of ACCESS_ONCE(), | |
500 | * but only when the compiler is aware of some particular ordering. One way | |
501 | * to make the compiler aware of ordering is to put the two invocations of | |
502 | * ACCESS_ONCE() in different C statements. | |
503 | * | |
927609d6 CB |
504 | * ACCESS_ONCE will only work on scalar types. For union types, ACCESS_ONCE |
505 | * on a union member will work as long as the size of the member matches the | |
506 | * size of the union and the size is smaller than word size. | |
507 | * | |
508 | * The major use cases of ACCESS_ONCE used to be (1) Mediating communication | |
509 | * between process-level code and irq/NMI handlers, all running on the same CPU, | |
510 | * and (2) Ensuring that the compiler does not fold, spindle, or otherwise | |
511 | * mutilate accesses that either do not require ordering or that interact | |
512 | * with an explicit memory barrier or atomic instruction that provides the | |
513 | * required ordering. | |
514 | * | |
663fdcbe | 515 | * If possible use READ_ONCE()/WRITE_ONCE() instead. |
9c3cdc1f | 516 | */ |
927609d6 | 517 | #define __ACCESS_ONCE(x) ({ \ |
c5b19946 | 518 | __maybe_unused typeof(x) __var = (__force typeof(x)) 0; \ |
927609d6 CB |
519 | (volatile typeof(x) *)&(x); }) |
520 | #define ACCESS_ONCE(x) (*__ACCESS_ONCE(x)) | |
9c3cdc1f | 521 | |
0a04b016 PZ |
522 | /** |
523 | * lockless_dereference() - safely load a pointer for later dereference | |
524 | * @p: The pointer to load | |
525 | * | |
526 | * Similar to rcu_dereference(), but for situations where the pointed-to | |
527 | * object's lifetime is managed by something other than RCU. That | |
528 | * "something other" might be reference counting or simple immortality. | |
331b6d8c PZ |
529 | * |
530 | * The seemingly unused void * variable is to validate @p is indeed a pointer | |
531 | * type. All pointer types silently cast to void *. | |
0a04b016 PZ |
532 | */ |
533 | #define lockless_dereference(p) \ | |
534 | ({ \ | |
38183b9c | 535 | typeof(p) _________p1 = READ_ONCE(p); \ |
331b6d8c | 536 | __maybe_unused const void * const _________p2 = _________p1; \ |
0a04b016 PZ |
537 | smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ |
538 | (_________p1); \ | |
539 | }) | |
540 | ||
324670b6 MH |
541 | /* Ignore/forbid kprobes attach on very low level functions marked by this attribute: */ |
542 | #ifdef CONFIG_KPROBES | |
543 | # define __kprobes __attribute__((__section__(".kprobes.text"))) | |
376e2424 | 544 | # define nokprobe_inline __always_inline |
324670b6 MH |
545 | #else |
546 | # define __kprobes | |
376e2424 | 547 | # define nokprobe_inline inline |
324670b6 | 548 | #endif |
1da177e4 | 549 | #endif /* __LINUX_COMPILER_H */ |