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RBIMPL_ALIGNOF: do not use __alignof__

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It is reported that on a system of i386 System V ABI, GCC returns 8 for
__alignof__(double).  OTOH the ABI defines alignments of double to be 4,
and ISO/IEC 9899:2011 reads that _Alignof(double) shall return 4 on such
machine.  What we want in ruby is 4 instead of 8 there.  We cannot use
__alignof__.

Additionally, both old GCC / old clang return 8 for _Alignof(double) on
such platforms.  They are their bugs, and already fixed in recent
versions.  But we have to support older compilers for a while.  Shall
check sanity of _Alignof.
This commit is contained in:
卜部昌平 2020-09-23 10:57:35 +09:00
parent fe875be01a
commit e9fb2bc873
Notes: git 2020-09-25 11:39:06 +09:00
2 changed files with 85 additions and 59 deletions
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86
include/ruby/internal/stdalign.h
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@ -22,16 +22,19 @@
*/
#include "ruby/internal/config.h"
#ifdef HAVE_STDALIGN_H
# include <stdalign.h>
#ifdef STDC_HEADERS
# include <stddef.h>
#endif
#include "ruby/internal/attr/artificial.h"
#include "ruby/internal/attr/const.h"
#include "ruby/internal/attr/constexpr.h"
#include "ruby/internal/attr/forceinline.h"
#include "ruby/internal/compiler_is.h"
#include "ruby/internal/compiler_since.h"
#include "ruby/internal/has/feature.h"
#include "ruby/internal/has/extension.h"
#include "ruby/internal/has/attribute.h"
#include "ruby/internal/has/declspec_attribute.h"
#include "ruby/internal/has/extension.h"
#include "ruby/internal/has/feature.h"
/**
* Wraps (or simulates) `alignas`. This is C++11's `alignas` and is _different_
@ -75,50 +78,55 @@
#endif
/**
* Wraps (or simulates) `alignof`. Unlike #RBIMPL_ALIGNAS, we can safely say
* both C/C++ definitions are effective.
* Wraps (or simulates) `alignof`.
*
* We want C11's `_Alignof`. However in spite of its clear language, compilers
* (including GCC and clang) tend to have buggy implementations. We have to
* avoid such things to resort to our own version.
*
* @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023
* @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560
* @see https://bugs.llvm.org/show_bug.cgi?id=26547
*/
#if defined(__cplusplus) && RBIMPL_HAS_EXTENSION(cxx_alignof)
# define RBIMPL_ALIGNOF __extension__ alignof
#if defined(__STDC_VERSION__) && defined(HAVE__ALIGNOF)
# /* Autoconf detected availability of a sane `_Alignof()`. */
# define RBIMPL_ALIGNOF(T) RB_GNUC_EXTENSION(_Alignof(T))
#elif defined(__cplusplus) && (__cplusplus >= 201103L)
# define RBIMPL_ALIGNOF alignof
#elif defined(__cplusplus)
# /* C++11 `alignof()` can be buggy. */
# /* see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560 */
# /* But don't worry, we can use templates and `constexpr`. */
# define RBIMPL_ALIGNOF(T) ruby::rbimpl_alignof<T>()
#elif defined(__INTEL_CXX11_MODE__)
# define RBIMPL_ALIGNOF alignof
#elif defined(__GXX_EXPERIMENTAL_CXX0X__)
# define RBIMPL_ALIGNOF alignof
#elif defined(__STDC_VERSION__) && RBIMPL_HAS_EXTENSION(c_alignof)
# define RBIMPL_ALIGNOF __extension__ _Alignof
#elif defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L)
# define RBIMPL_ALIGNOF _Alignof
namespace ruby {
template<typename T>
RBIMPL_ATTR_CONSTEXPR(CXX11)
RBIMPL_ATTR_ARTIFICIAL()
RBIMPL_ATTR_FORCEINLINE()
RBIMPL_ATTR_CONST()
static size_t
rbimpl_alignof()
{
typedef struct {
char _;
T t;
} type;
return offsetof(type, t);
}
}
#elif RBIMPL_COMPILER_IS(MSVC)
# /* Windows have no alignment glitch.*/
# define RBIMPL_ALIGNOF __alignof
#elif defined(__GNUC__)
# /* At least GCC 2.95 had this. */
# define RBIMPL_ALIGNOF __extension__ __alignof__
#elif defined(__alignof_is_defined) || defined(__DOXYGEN__)
# /* OK, we can safely take <stdalign.h> definition. */
# define RBIMPL_ALIGNOF alignof
#elif RBIMPL_COMPILER_SINCE(SunPro, 5, 9, 0)
# /* According to their manual, Sun Studio 12 introduced __alignof__ for both
# * C/C++. */
# define RBIMPL_ALIGNOF __alignof__
#elif 0
# /* THIS IS NG, you cannot define a new type inside of offsetof. */
#else
# /* :BEWARE: It is an undefined behaviour to define a struct/union inside of
# * `offsetof()`! This section is the last resort. If your compiler somehow
# * supports querying alignment of a type please add your own definition of
# * `RBIMPL_ALIGNOF` instead. */
# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm */
# define RBIMPL_ALIGNOF(T) offsetof(struct { char _; T t; }, t)
#else
# error :FIXME: add your compiler here to obtain an alignment.
#endif
#endif /* RBIMPL_STDALIGN_H */