include/wrapper/compiler.h

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * wrapper/compiler.h
   4  *
   5  * Copyright (C) 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   6  */
   7
   8 #ifndef _LTTNG_WRAPPER_COMPILER_H
   9 #define _LTTNG_WRAPPER_COMPILER_H
  10
  11 #include <linux/compiler.h>
  12 #include <linux/version.h>
  13
  14 /*
  15  * Don't allow compiling with buggy compiler.
  16  */
  17
  18 #ifdef GCC_VERSION
  19
  20 /*
  21  * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58854
  22  */
  23 # ifdef __ARMEL__
  24 #  if GCC_VERSION >= 40800 && GCC_VERSION <= 40802
  25 #   error Your gcc version produces clobbered frame accesses
  26 #  endif
  27 # endif
  28 #endif
  29
  30 /*
  31  * READ/WRITE_ONCE were introduced in kernel 3.19 and ACCESS_ONCE
  32  * was removed in 4.15. Prefer READ/WRITE but fallback to ACCESS
  33  * when they are not available.
  34  */
  35 #ifndef READ_ONCE
  36 # define READ_ONCE(x)           ACCESS_ONCE(x)
  37 #endif
  38
  39 #ifndef WRITE_ONCE
  40 # define WRITE_ONCE(x, val)     ({ ACCESS_ONCE(x) = val; })
  41 #endif
  42
  43 /*
  44  * In v4.15 a smp read barrier was added to READ_ONCE to replace
  45  * lockless_dereference(), replicate this behavior on prior kernels
  46  * and remove calls to smp_read_barrier_depends which was dropped
  47  * in v5.9.
  48  */
  49 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,15,0))
  50 #define LTTNG_READ_ONCE(x)      READ_ONCE(x)
  51 #else
  52 #define LTTNG_READ_ONCE(x)                      \
  53 ({                                              \
  54         typeof(x) __val = READ_ONCE(x);         \
  55         smp_read_barrier_depends();             \
  56         __val;                                  \
  57 })
  58 #endif
  59
  60 #define __LTTNG_COMPOUND_LITERAL(type, ...)     (type[]) { __VA_ARGS__ }
  61
  62 #endif /* _LTTNG_WRAPPER_COMPILER_H */