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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 
 13 /* Optimization barrier */
 14 /* The "volatile" is due to gcc bugs */
 15 #define barrier() __asm__ __volatile__("": : :"memory")
 16 
 17 /*
 18  * This macro obfuscates arithmetic on a variable address so that gcc
 19  * shouldn't recognize the original var, and make assumptions about it.
 20  *
 21  * This is needed because the C standard makes it undefined to do
 22  * pointer arithmetic on "objects" outside their boundaries and the
 23  * gcc optimizers assume this is the case. In particular they
 24  * assume such arithmetic does not wrap.
 25  *
 26  * A miscompilation has been observed because of this on PPC.
 27  * To work around it we hide the relationship of the pointer and the object
 28  * using this macro.
 29  *
 30  * Versions of the ppc64 compiler before 4.1 had a bug where use of
 31  * RELOC_HIDE could trash r30. The bug can be worked around by changing
 32  * the inline assembly constraint from =g to =r, in this particular
 33  * case either is valid.
 34  */
 35 #define RELOC_HIDE(ptr, off)                                    \
 36   ({ unsigned long __ptr;                                       \
 37     __asm__ ("" : "=r"(__ptr) : ""(ptr));              \
 38     (typeof(ptr)) (__ptr + (off)); })
 39 
 40 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
 41 #define OPTIMIZER_HIDE_VAR(var) __asm__ ("" : "=r" (var) : "" (var))
 42 
 43 #ifdef __CHECKER__
 44 #define __must_be_array(arr) 0
 45 #else
 46 /* &a[0] degrades to a pointer: a different type from an array */
 47 #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 48 #endif
 49 
 50 /*
 51  * Force always-inline if the user requests it so via the .config,
 52  * or if gcc is too old:
 53  */
 54 #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
 55     !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
 56 # define inline         inline          __attribute__((always_inline)) notrace
 57 # define __inline__     __inline__      __attribute__((always_inline)) notrace
 58 # define __inline       __inline        __attribute__((always_inline)) notrace
 59 #else
 60 /* A lot of inline functions can cause havoc with function tracing */
 61 # define inline         inline          notrace
 62 # define __inline__     __inline__      notrace
 63 # define __inline       __inline        notrace
 64 #endif
 65 
 66 #define __deprecated                    __attribute__((deprecated))
 67 #define __packed                        __attribute__((packed))
 68 #define __weak                          __attribute__((weak))
 69 
 70 /*
 71  * it doesn't make sense on ARM (currently the only user of __naked) to trace
 72  * naked functions because then mcount is called without stack and frame pointer
 73  * being set up and there is no chance to restore the lr register to the value
 74  * before mcount was called.
 75  *
 76  * The asm() bodies of naked functions often depend on standard calling conventions,
 77  * therefore they must be noinline and noclone.  GCC 4.[56] currently fail to enforce
 78  * this, so we must do so ourselves.  See GCC PR44290.
 79  */
 80 #define __naked                         __attribute__((naked)) noinline __noclone notrace
 81 
 82 #define __noreturn                      __attribute__((noreturn))
 83 
 84 /*
 85  * From the GCC manual:
 86  *
 87  * Many functions have no effects except the return value and their
 88  * return value depends only on the parameters and/or global
 89  * variables.  Such a function can be subject to common subexpression
 90  * elimination and loop optimization just as an arithmetic operator
 91  * would be.
 92  * [...]
 93  */
 94 #define __pure                          __attribute__((pure))
 95 #define __aligned(x)                    __attribute__((aligned(x)))
 96 #define __printf(a, b)                  __attribute__((format(printf, a, b)))
 97 #define __scanf(a, b)                   __attribute__((format(scanf, a, b)))
 98 #define  noinline                       __attribute__((noinline))
 99 #define __attribute_const__             __attribute__((__const__))
100 #define __maybe_unused                  __attribute__((unused))
101 #define __always_unused                 __attribute__((unused))
102 
103 /* gcc version specific checks */
104 
105 #if GCC_VERSION < 30200
106 # error Sorry, your compiler is too old - please upgrade it.
107 #endif
108 
109 #if GCC_VERSION < 30300
110 # define __used                 __attribute__((__unused__))
111 #else
112 # define __used                 __attribute__((__used__))
113 #endif
114 
115 #ifdef CONFIG_GCOV_KERNEL
116 # if GCC_VERSION < 30400
117 #   error "GCOV profiling support for gcc versions below 3.4 not included"
118 # endif /* __GNUC_MINOR__ */
119 #endif /* CONFIG_GCOV_KERNEL */
120 
121 #if GCC_VERSION >= 30400
122 #define __must_check            __attribute__((warn_unused_result))
123 #endif
124 
125 #if GCC_VERSION >= 40000
126 
127 /* GCC 4.1.[01] miscompiles __weak */
128 #ifdef __KERNEL__
129 # if GCC_VERSION >= 40100 &&  GCC_VERSION <= 40101
130 #  error Your version of gcc miscompiles the __weak directive
131 # endif
132 #endif
133 
134 #define __used                  __attribute__((__used__))
135 #define __compiler_offsetof(a, b)                                       \
136         __builtin_offsetof(a, b)
137 
138 #if GCC_VERSION >= 40100 && GCC_VERSION < 40600
139 # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
140 #endif
141 
142 #if GCC_VERSION >= 40300
143 /* Mark functions as cold. gcc will assume any path leading to a call
144  * to them will be unlikely.  This means a lot of manual unlikely()s
145  * are unnecessary now for any paths leading to the usual suspects
146  * like BUG(), printk(), panic() etc. [but let's keep them for now for
147  * older compilers]
148  *
149  * Early snapshots of gcc 4.3 don't support this and we can't detect this
150  * in the preprocessor, but we can live with this because they're unreleased.
151  * Maketime probing would be overkill here.
152  *
153  * gcc also has a __attribute__((__hot__)) to move hot functions into
154  * a special section, but I don't see any sense in this right now in
155  * the kernel context
156  */
157 #define __cold                  __attribute__((__cold__))
158 
159 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
160 
161 #ifndef __CHECKER__
162 # define __compiletime_warning(message) __attribute__((warning(message)))
163 # define __compiletime_error(message) __attribute__((error(message)))
164 #endif /* __CHECKER__ */
165 #endif /* GCC_VERSION >= 40300 */
166 
167 #if GCC_VERSION >= 40500
168 /*
169  * Mark a position in code as unreachable.  This can be used to
170  * suppress control flow warnings after asm blocks that transfer
171  * control elsewhere.
172  *
173  * Early snapshots of gcc 4.5 don't support this and we can't detect
174  * this in the preprocessor, but we can live with this because they're
175  * unreleased.  Really, we need to have autoconf for the kernel.
176  */
177 #define unreachable() __builtin_unreachable()
178 
179 /* Mark a function definition as prohibited from being cloned. */
180 #define __noclone       __attribute__((__noclone__, __optimize__("no-tracer")))
181 
182 #endif /* GCC_VERSION >= 40500 */
183 
184 #if GCC_VERSION >= 40600
185 /*
186  * Tell the optimizer that something else uses this function or variable.
187  */
188 #define __visible       __attribute__((externally_visible))
189 #endif
190 
191 /*
192  * GCC 'asm goto' miscompiles certain code sequences:
193  *
194  *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
195  *
196  * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
197  *
198  * (asm goto is automatically volatile - the naming reflects this.)
199  */
200 #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
201 
202 #ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
203 #if GCC_VERSION >= 40400
204 #define __HAVE_BUILTIN_BSWAP32__
205 #define __HAVE_BUILTIN_BSWAP64__
206 #endif
207 #if GCC_VERSION >= 40800 || (defined(__powerpc__) && GCC_VERSION >= 40600)
208 #define __HAVE_BUILTIN_BSWAP16__
209 #endif
210 #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */
211 
212 #if GCC_VERSION >= 50000
213 #define KASAN_ABI_VERSION 4
214 #elif GCC_VERSION >= 40902
215 #define KASAN_ABI_VERSION 3
216 #endif
217 
218 #endif  /* gcc version >= 40000 specific checks */
219 
220 #if !defined(__noclone)
221 #define __noclone       /* not needed */
222 #endif
223 
224 /*
225  * A trick to suppress uninitialized variable warning without generating any
226  * code
227  */
228 #define uninitialized_var(x) x = x
229 
230 #define __always_inline         inline __attribute__((always_inline))
231 

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