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Linux/include/linux/compiler-gcc.h

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  1 #ifndef __LINUX_COMPILER_H
  2 #error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
  3 #endif
  4 
  5 /*
  6  * Common definitions for all gcc versions go here.
  7  */
  8 #define GCC_VERSION (__GNUC__ * 10000           \
  9                      + __GNUC_MINOR__ * 100     \
 10                      + __GNUC_PATCHLEVEL__)
 11 
 12 /* Optimization barrier */
 13 
 14 /* The "volatile" is due to gcc bugs */
 15 #define barrier() __asm__ __volatile__("": : :"memory")
 16 /*
 17  * This version is i.e. to prevent dead stores elimination on @ptr
 18  * where gcc and llvm may behave differently when otherwise using
 19  * normal barrier(): while gcc behavior gets along with a normal
 20  * barrier(), llvm needs an explicit input variable to be assumed
 21  * clobbered. The issue is as follows: while the inline asm might
 22  * access any memory it wants, the compiler could have fit all of
 23  * @ptr into memory registers instead, and since @ptr never escaped
 24  * from that, it proved that the inline asm wasn't touching any of
 25  * it. This version works well with both compilers, i.e. we're telling
 26  * the compiler that the inline asm absolutely may see the contents
 27  * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
 28  */
 29 #define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
 30 
 31 /*
 32  * This macro obfuscates arithmetic on a variable address so that gcc
 33  * shouldn't recognize the original var, and make assumptions about it.
 34  *
 35  * This is needed because the C standard makes it undefined to do
 36  * pointer arithmetic on "objects" outside their boundaries and the
 37  * gcc optimizers assume this is the case. In particular they
 38  * assume such arithmetic does not wrap.
 39  *
 40  * A miscompilation has been observed because of this on PPC.
 41  * To work around it we hide the relationship of the pointer and the object
 42  * using this macro.
 43  *
 44  * Versions of the ppc64 compiler before 4.1 had a bug where use of
 45  * RELOC_HIDE could trash r30. The bug can be worked around by changing
 46  * the inline assembly constraint from =g to =r, in this particular
 47  * case either is valid.
 48  */
 49 #define RELOC_HIDE(ptr, off)                                            \
 50 ({                                                                      \
 51         unsigned long __ptr;                                            \
 52         __asm__ ("" : "=r"(__ptr) : ""(ptr));                          \
 53         (typeof(ptr)) (__ptr + (off));                                  \
 54 })
 55 
 56 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
 57 #define OPTIMIZER_HIDE_VAR(var)                                         \
 58         __asm__ ("" : "=r" (var) : "" (var))
 59 
 60 #ifdef __CHECKER__
 61 #define __must_be_array(a)      0
 62 #else
 63 /* &a[0] degrades to a pointer: a different type from an array */
 64 #define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 65 #endif
 66 
 67 /*
 68  * Force always-inline if the user requests it so via the .config,
 69  * or if gcc is too old:
 70  */
 71 #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||                \
 72     !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
 73 #define inline          inline          __attribute__((always_inline)) notrace
 74 #define __inline__      __inline__      __attribute__((always_inline)) notrace
 75 #define __inline        __inline        __attribute__((always_inline)) notrace
 76 #else
 77 /* A lot of inline functions can cause havoc with function tracing */
 78 #define inline          inline          notrace
 79 #define __inline__      __inline__      notrace
 80 #define __inline        __inline        notrace
 81 #endif
 82 
 83 #define __always_inline inline __attribute__((always_inline))
 84 #define  noinline       __attribute__((noinline))
 85 
 86 #define __deprecated    __attribute__((deprecated))
 87 #define __packed        __attribute__((packed))
 88 #define __weak          __attribute__((weak))
 89 #define __alias(symbol) __attribute__((alias(#symbol)))
 90 
 91 /*
 92  * it doesn't make sense on ARM (currently the only user of __naked)
 93  * to trace naked functions because then mcount is called without
 94  * stack and frame pointer being set up and there is no chance to
 95  * restore the lr register to the value before mcount was called.
 96  *
 97  * The asm() bodies of naked functions often depend on standard calling
 98  * conventions, therefore they must be noinline and noclone.
 99  *
100  * GCC 4.[56] currently fail to enforce this, so we must do so ourselves.
101  * See GCC PR44290.
102  */
103 #define __naked         __attribute__((naked)) noinline __noclone notrace
104 
105 #define __noreturn      __attribute__((noreturn))
106 
107 /*
108  * From the GCC manual:
109  *
110  * Many functions have no effects except the return value and their
111  * return value depends only on the parameters and/or global
112  * variables.  Such a function can be subject to common subexpression
113  * elimination and loop optimization just as an arithmetic operator
114  * would be.
115  * [...]
116  */
117 #define __pure                  __attribute__((pure))
118 #define __aligned(x)            __attribute__((aligned(x)))
119 #define __aligned_largest       __attribute__((aligned))
120 #define __printf(a, b)          __attribute__((format(printf, a, b)))
121 #define __scanf(a, b)           __attribute__((format(scanf, a, b)))
122 #define __attribute_const__     __attribute__((__const__))
123 #define __maybe_unused          __attribute__((unused))
124 #define __always_unused         __attribute__((unused))
125 #define __mode(x)               __attribute__((mode(x)))
126 
127 /* gcc version specific checks */
128 
129 #if GCC_VERSION < 30200
130 # error Sorry, your compiler is too old - please upgrade it.
131 #endif
132 
133 #if GCC_VERSION < 30300
134 # define __used                 __attribute__((__unused__))
135 #else
136 # define __used                 __attribute__((__used__))
137 #endif
138 
139 #ifdef CONFIG_GCOV_KERNEL
140 # if GCC_VERSION < 30400
141 #   error "GCOV profiling support for gcc versions below 3.4 not included"
142 # endif /* __GNUC_MINOR__ */
143 #endif /* CONFIG_GCOV_KERNEL */
144 
145 #if GCC_VERSION >= 30400
146 #define __must_check            __attribute__((warn_unused_result))
147 #define __malloc                __attribute__((__malloc__))
148 #endif
149 
150 #if GCC_VERSION >= 40000
151 
152 /* GCC 4.1.[01] miscompiles __weak */
153 #ifdef __KERNEL__
154 # if GCC_VERSION >= 40100 &&  GCC_VERSION <= 40101
155 #  error Your version of gcc miscompiles the __weak directive
156 # endif
157 #endif
158 
159 #define __used                  __attribute__((__used__))
160 #define __compiler_offsetof(a, b)                                       \
161         __builtin_offsetof(a, b)
162 
163 #if GCC_VERSION >= 40100
164 # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
165 #endif
166 
167 #if GCC_VERSION >= 40300
168 /* Mark functions as cold. gcc will assume any path leading to a call
169  * to them will be unlikely.  This means a lot of manual unlikely()s
170  * are unnecessary now for any paths leading to the usual suspects
171  * like BUG(), printk(), panic() etc. [but let's keep them for now for
172  * older compilers]
173  *
174  * Early snapshots of gcc 4.3 don't support this and we can't detect this
175  * in the preprocessor, but we can live with this because they're unreleased.
176  * Maketime probing would be overkill here.
177  *
178  * gcc also has a __attribute__((__hot__)) to move hot functions into
179  * a special section, but I don't see any sense in this right now in
180  * the kernel context
181  */
182 #define __cold                  __attribute__((__cold__))
183 
184 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
185 
186 #ifndef __CHECKER__
187 # define __compiletime_warning(message) __attribute__((warning(message)))
188 # define __compiletime_error(message) __attribute__((error(message)))
189 #endif /* __CHECKER__ */
190 #endif /* GCC_VERSION >= 40300 */
191 
192 #if GCC_VERSION >= 40500
193 
194 #ifndef __CHECKER__
195 #ifdef LATENT_ENTROPY_PLUGIN
196 #define __latent_entropy __attribute__((latent_entropy))
197 #endif
198 #endif
199 
200 #ifdef CONFIG_STACK_VALIDATION
201 #define annotate_unreachable() ({                                       \
202         asm("%c0:\t\n"                                                  \
203             ".pushsection .discard.unreachable\t\n"                     \
204             ".long %c0b - .\t\n"                                        \
205             ".popsection\t\n" : : "i" (__LINE__));                      \
206 })
207 #else
208 #define annotate_unreachable()
209 #endif
210 
211 /*
212  * Mark a position in code as unreachable.  This can be used to
213  * suppress control flow warnings after asm blocks that transfer
214  * control elsewhere.
215  *
216  * Early snapshots of gcc 4.5 don't support this and we can't detect
217  * this in the preprocessor, but we can live with this because they're
218  * unreleased.  Really, we need to have autoconf for the kernel.
219  */
220 #define unreachable() \
221         do { annotate_unreachable(); __builtin_unreachable(); } while (0)
222 
223 /* Mark a function definition as prohibited from being cloned. */
224 #define __noclone       __attribute__((__noclone__, __optimize__("no-tracer")))
225 
226 #endif /* GCC_VERSION >= 40500 */
227 
228 #if GCC_VERSION >= 40600
229 /*
230  * When used with Link Time Optimization, gcc can optimize away C functions or
231  * variables which are referenced only from assembly code.  __visible tells the
232  * optimizer that something else uses this function or variable, thus preventing
233  * this.
234  */
235 #define __visible       __attribute__((externally_visible))
236 #endif
237 
238 
239 #if GCC_VERSION >= 40900 && !defined(__CHECKER__)
240 /*
241  * __assume_aligned(n, k): Tell the optimizer that the returned
242  * pointer can be assumed to be k modulo n. The second argument is
243  * optional (default 0), so we use a variadic macro to make the
244  * shorthand.
245  *
246  * Beware: Do not apply this to functions which may return
247  * ERR_PTRs. Also, it is probably unwise to apply it to functions
248  * returning extra information in the low bits (but in that case the
249  * compiler should see some alignment anyway, when the return value is
250  * massaged by 'flags = ptr & 3; ptr &= ~3;').
251  */
252 #define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
253 #endif
254 
255 /*
256  * GCC 'asm goto' miscompiles certain code sequences:
257  *
258  *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
259  *
260  * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
261  *
262  * (asm goto is automatically volatile - the naming reflects this.)
263  */
264 #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
265 
266 /*
267  * sparse (__CHECKER__) pretends to be gcc, but can't do constant
268  * folding in __builtin_bswap*() (yet), so don't set these for it.
269  */
270 #if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP) && !defined(__CHECKER__)
271 #if GCC_VERSION >= 40400
272 #define __HAVE_BUILTIN_BSWAP32__
273 #define __HAVE_BUILTIN_BSWAP64__
274 #endif
275 #if GCC_VERSION >= 40800
276 #define __HAVE_BUILTIN_BSWAP16__
277 #endif
278 #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP && !__CHECKER__ */
279 
280 #if GCC_VERSION >= 70000
281 #define KASAN_ABI_VERSION 5
282 #elif GCC_VERSION >= 50000
283 #define KASAN_ABI_VERSION 4
284 #elif GCC_VERSION >= 40902
285 #define KASAN_ABI_VERSION 3
286 #endif
287 
288 #if GCC_VERSION >= 40902
289 /*
290  * Tell the compiler that address safety instrumentation (KASAN)
291  * should not be applied to that function.
292  * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
293  */
294 #define __no_sanitize_address __attribute__((no_sanitize_address))
295 #endif
296 
297 #endif  /* gcc version >= 40000 specific checks */
298 
299 #if !defined(__noclone)
300 #define __noclone       /* not needed */
301 #endif
302 
303 #if !defined(__no_sanitize_address)
304 #define __no_sanitize_address
305 #endif
306 
307 /*
308  * A trick to suppress uninitialized variable warning without generating any
309  * code
310  */
311 #define uninitialized_var(x) x = x
312 

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