compiler-gcc.h 9.5 KB

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