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f401668306
This does exactly the same as ALREADY_CHECKED() but does it inline, returning an identical copy of the scalar variable without letting the compiler know how it might have been transformed. This can forcefully disable certain null-pointer checks or result checks when known undesirable. Typically forcing a crash with *(DISGUISE(NULL))=0 will not cause a null-deref warning.
204 lines
6.3 KiB
C
204 lines
6.3 KiB
C
/*
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* include/common/compiler.h
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* This files contains some compiler-specific settings.
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*
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* Copyright (C) 2000-2009 Willy Tarreau - w@1wt.eu
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation, version 2.1
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* exclusively.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef _COMMON_COMPILER_H
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#define _COMMON_COMPILER_H
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/*
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* Gcc before 3.0 needs [0] to declare a variable-size array
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*/
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#ifndef VAR_ARRAY
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#if __GNUC__ < 3
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#define VAR_ARRAY 0
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#else
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#define VAR_ARRAY
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#endif
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#endif
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/* By default, gcc does not inline large chunks of code, but we want it to
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* respect our choices.
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*/
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#if !defined(forceinline)
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#if __GNUC__ < 3
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#define forceinline inline
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#else
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#define forceinline inline __attribute__((always_inline))
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#endif
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#endif
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/* silence the "unused" warnings without having to place painful #ifdefs.
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* For use with variables or functions.
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*/
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#define __maybe_unused __attribute__((unused))
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/* This allows gcc to know that some locations are never reached, for example
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* after a longjmp() in the Lua code, hence that some errors caught by such
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* methods cannot propagate further. This is important with gcc versions 6 and
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* above which can more aggressively detect null dereferences. The builtin
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* below was introduced in gcc 4.5, and before it we didn't care.
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*/
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#if __GNUC__ >= 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
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#define my_unreachable() __builtin_unreachable()
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#else
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#define my_unreachable()
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#endif
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/* This macro may be used to block constant propagation that lets the compiler
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* detect a possible NULL dereference on a variable resulting from an explicit
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* assignment in an impossible check. Sometimes a function is called which does
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* safety checks and returns NULL if safe conditions are not met. The place
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* where it's called cannot hit this condition and dereferencing the pointer
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* without first checking it will make the compiler emit a warning about a
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* "potential null pointer dereference" which is hard to work around. This
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* macro "washes" the pointer and prevents the compiler from emitting tests
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* branching to undefined instructions. It may only be used when the developer
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* is absolutely certain that the conditions are guaranteed and that the
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* pointer passed in argument cannot be NULL by design.
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*/
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#define ALREADY_CHECKED(p) do { asm("" : "=rm"(p) : "0"(p)); } while (0)
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/* same as above but to be used to pass the input value to the output but
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* without letting the compiler know about its initial properties.
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*/
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#define DISGUISE(v) ({ typeof(v) __v = (v); ALREADY_CHECKED(__v); __v; })
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/*
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* Gcc >= 3 provides the ability for the program to give hints to the
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* compiler about what branch of an if is most likely to be taken. This
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* helps the compiler produce the most compact critical paths, which is
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* generally better for the cache and to reduce the number of jumps.
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*/
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#if !defined(likely)
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#if __GNUC__ < 3
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#define __builtin_expect(x,y) (x)
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#define likely(x) (x)
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#define unlikely(x) (x)
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#else
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#define likely(x) (__builtin_expect((x) != 0, 1))
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#define unlikely(x) (__builtin_expect((x) != 0, 0))
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#endif
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#endif
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#ifndef __GNUC_PREREQ__
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#if defined(__GNUC__) && !defined(__INTEL_COMPILER)
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#define __GNUC_PREREQ__(ma, mi) \
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(__GNUC__ > (ma) || __GNUC__ == (ma) && __GNUC_MINOR__ >= (mi))
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#else
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#define __GNUC_PREREQ__(ma, mi) 0
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#endif
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#endif
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#ifndef offsetof
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#if __GNUC_PREREQ__(4, 1)
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#define offsetof(type, field) __builtin_offsetof(type, field)
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#else
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#define offsetof(type, field) \
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((size_t)(uintptr_t)((const volatile void *)&((type *)0)->field))
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#endif
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#endif
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/* Some architectures have a double-word CAS, sometimes even dual-8 bytes.
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* Some architectures support unaligned accesses, others are fine with them
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* but only for non-atomic operations. Also mention those supporting unaligned
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* accesses and being little endian, and those where unaligned accesses are
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* known to be fast (almost as fast as aligned ones).
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*/
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#if defined(__x86_64__)
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#define HA_UNALIGNED
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#define HA_UNALIGNED_LE
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#define HA_UNALIGNED_LE64
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#define HA_UNALIGNED_FAST
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#define HA_UNALIGNED_ATOMIC
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#define HA_HAVE_CAS_DW
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#define HA_CAS_IS_8B
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#elif defined(__i386__) || defined(__i486__) || defined(__i586__) || defined(__i686__)
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#define HA_UNALIGNED
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#define HA_UNALIGNED_LE
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#define HA_UNALIGNED_ATOMIC
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#elif defined (__aarch64__) || defined(__ARM_ARCH_8A)
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#define HA_UNALIGNED
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#define HA_UNALIGNED_LE
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#define HA_UNALIGNED_LE64
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#define HA_UNALIGNED_FAST
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#define HA_HAVE_CAS_DW
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#define HA_CAS_IS_8B
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#elif defined(__arm__) && (defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__))
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#define HA_UNALIGNED
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#define HA_UNALIGNED_LE
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#define HA_UNALIGNED_FAST
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#define HA_HAVE_CAS_DW
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#endif
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/* sets alignment for current field or variable */
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#ifndef ALIGNED
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#define ALIGNED(x) __attribute__((aligned(x)))
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#endif
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/* sets alignment only on architectures preventing unaligned atomic accesses */
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#ifndef MAYBE_ALIGNED
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#ifndef HA_UNALIGNED
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#define MAYBE_ALIGNED(x) ALIGNED(x)
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#else
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#define MAYBE_ALIGNED(x)
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#endif
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#endif
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/* sets alignment only on architectures preventing unaligned atomic accesses */
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#ifndef ATOMIC_ALIGNED
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#ifndef HA_UNALIGNED_ATOMIC
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#define ATOMIC_ALIGNED(x) ALIGNED(x)
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#else
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#define ATOMIC_ALIGNED(x)
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#endif
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#endif
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/* add a mandatory alignment for next fields in a structure */
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#ifndef ALWAYS_ALIGN
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#define ALWAYS_ALIGN(x) union { } ALIGNED(x)
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#endif
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/* add an optional alignment for next fields in a structure, only for archs
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* which do not support unaligned accesses.
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*/
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#ifndef MAYBE_ALIGN
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#ifndef HA_UNALIGNED
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#define MAYBE_ALIGN(x) union { } ALIGNED(x)
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#else
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#define MAYBE_ALIGN(x)
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#endif
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#endif
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/* add an optional alignment for next fields in a structure, only for archs
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* which do not support unaligned accesses for atomic operations.
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*/
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#ifndef ATOMIC_ALIGN
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#ifndef HA_UNALIGNED_ATOMIC
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#define ATOMIC_ALIGN(x) union { } ALIGNED(x)
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#else
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#define ATOMIC_ALIGN(x)
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#endif
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#endif
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#endif /* _COMMON_COMPILER_H */
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