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RBIMPL_ALIGNOF: do not use __alignof__
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.
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卜部昌平
parent
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commit
e9fb2bc873
Notes:
git
2020-09-25 11:39:06 +09:00
2 changed files with 85 additions and 59 deletions
58
configure.ac
58
configure.ac
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@ -1460,26 +1460,44 @@ AS_IF([test "$rb_cv_va_args_macro" = yes], [
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AC_DEFINE(HAVE_VA_ARGS_MACRO)
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])
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AC_CACHE_CHECK([for alignof() syntax], rb_cv_have_alignof,[
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rb_cv_have_alignof=no
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# Prefer alignof over _Alignof to allow C++ compiler to read ruby.h
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RUBY_WERROR_FLAG([
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for expr in \
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"alignof" \
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"_Alignof" \
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"__alignof" \
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"__alignof__" \
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;
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do
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AC_TRY_COMPILE([
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@%:@ifdef HAVE_STDALIGN_H
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@%:@include <stdalign.h>
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@%:@endif],[return (int)$expr(int);],
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[rb_cv_have_alignof="$expr"; break], [])
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done
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])])
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AS_IF([test "$rb_cv_have_alignof" != no], [
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AC_DEFINE_UNQUOTED(RUBY_ALIGNOF, $rb_cv_have_alignof)
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# We want C11's `_Alignof`. GCC (and alike) have `__alignof__`, which behave
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# slightly differently than the C11's. We cannot use `__alignof__` for our
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# purpose. The problem is, however, that old gcc and old clang had both
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# implemented `_Alignof` as a synonym of `__alignof__`. They are not what we
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# want. We have to check sanity.
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#
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# See also: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023
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# See also: https://bugs.llvm.org/show_bug.cgi?id=26547
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AC_CACHE_CHECK([if _Alignof() works], rb_cv_have__alignof,[
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rb_cv_have__alignof=no
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RUBY_WERROR_FLAG([
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AC_TRY_COMPILE([
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@%:@ifdef HAVE_STDALIGN_H
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@%:@include <stdalign.h>
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@%:@endif
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@%:@ifdef STDC_HEADERS
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@%:@include <stddef.h>
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@%:@endif
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@%:@ifndef __GNUC__
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@%:@define __extension__
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@%:@endif
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], [
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typedef struct conftest_tag {
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char _;
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double d;
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} T;
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static int conftest_ary@<:@
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offsetof(T, d) == __extension__ _Alignof(double)
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? 1 : -1
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@:>@;
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return conftest_ary@<:@0@:>@;
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], [
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rb_cv_have__alignof=yes
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])
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])
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])
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AS_IF([test "$rb_cv_have__alignof" != no], [
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AC_DEFINE(HAVE__ALIGNOF)
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])
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RUBY_FUNC_ATTRIBUTE(__const__, CONSTFUNC)
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@ -22,16 +22,19 @@
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*/
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#include "ruby/internal/config.h"
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#ifdef HAVE_STDALIGN_H
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# include <stdalign.h>
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#ifdef STDC_HEADERS
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# include <stddef.h>
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#endif
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#include "ruby/internal/attr/artificial.h"
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#include "ruby/internal/attr/const.h"
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#include "ruby/internal/attr/constexpr.h"
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#include "ruby/internal/attr/forceinline.h"
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#include "ruby/internal/compiler_is.h"
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#include "ruby/internal/compiler_since.h"
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#include "ruby/internal/has/feature.h"
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#include "ruby/internal/has/extension.h"
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#include "ruby/internal/has/attribute.h"
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#include "ruby/internal/has/declspec_attribute.h"
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#include "ruby/internal/has/extension.h"
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#include "ruby/internal/has/feature.h"
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/**
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* Wraps (or simulates) `alignas`. This is C++11's `alignas` and is _different_
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@ -75,50 +78,55 @@
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#endif
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/**
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* Wraps (or simulates) `alignof`. Unlike #RBIMPL_ALIGNAS, we can safely say
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* both C/C++ definitions are effective.
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* Wraps (or simulates) `alignof`.
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*
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* We want C11's `_Alignof`. However in spite of its clear language, compilers
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* (including GCC and clang) tend to have buggy implementations. We have to
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* avoid such things to resort to our own version.
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*
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* @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023
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* @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560
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* @see https://bugs.llvm.org/show_bug.cgi?id=26547
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*/
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#if defined(__cplusplus) && RBIMPL_HAS_EXTENSION(cxx_alignof)
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# define RBIMPL_ALIGNOF __extension__ alignof
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#if defined(__STDC_VERSION__) && defined(HAVE__ALIGNOF)
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# /* Autoconf detected availability of a sane `_Alignof()`. */
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# define RBIMPL_ALIGNOF(T) RB_GNUC_EXTENSION(_Alignof(T))
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#elif defined(__cplusplus) && (__cplusplus >= 201103L)
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# define RBIMPL_ALIGNOF alignof
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#elif defined(__cplusplus)
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# /* C++11 `alignof()` can be buggy. */
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# /* see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560 */
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# /* But don't worry, we can use templates and `constexpr`. */
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# define RBIMPL_ALIGNOF(T) ruby::rbimpl_alignof<T>()
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#elif defined(__INTEL_CXX11_MODE__)
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# define RBIMPL_ALIGNOF alignof
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#elif defined(__GXX_EXPERIMENTAL_CXX0X__)
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# define RBIMPL_ALIGNOF alignof
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#elif defined(__STDC_VERSION__) && RBIMPL_HAS_EXTENSION(c_alignof)
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# define RBIMPL_ALIGNOF __extension__ _Alignof
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#elif defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L)
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# define RBIMPL_ALIGNOF _Alignof
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namespace ruby {
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template<typename T>
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RBIMPL_ATTR_CONSTEXPR(CXX11)
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RBIMPL_ATTR_ARTIFICIAL()
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RBIMPL_ATTR_FORCEINLINE()
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RBIMPL_ATTR_CONST()
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static size_t
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rbimpl_alignof()
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{
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typedef struct {
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char _;
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T t;
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} type;
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return offsetof(type, t);
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}
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}
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#elif RBIMPL_COMPILER_IS(MSVC)
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# /* Windows have no alignment glitch.*/
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# define RBIMPL_ALIGNOF __alignof
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#elif defined(__GNUC__)
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# /* At least GCC 2.95 had this. */
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# define RBIMPL_ALIGNOF __extension__ __alignof__
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#elif defined(__alignof_is_defined) || defined(__DOXYGEN__)
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# /* OK, we can safely take <stdalign.h> definition. */
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# define RBIMPL_ALIGNOF alignof
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#elif RBIMPL_COMPILER_SINCE(SunPro, 5, 9, 0)
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# /* According to their manual, Sun Studio 12 introduced __alignof__ for both
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# * C/C++. */
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# define RBIMPL_ALIGNOF __alignof__
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#elif 0
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# /* THIS IS NG, you cannot define a new type inside of offsetof. */
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#else
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# /* :BEWARE: It is an undefined behaviour to define a struct/union inside of
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# * `offsetof()`! This section is the last resort. If your compiler somehow
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# * supports querying alignment of a type please add your own definition of
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# * `RBIMPL_ALIGNOF` instead. */
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# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm */
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# define RBIMPL_ALIGNOF(T) offsetof(struct { char _; T t; }, t)
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#else
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# error :FIXME: add your compiler here to obtain an alignment.
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#endif
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#endif /* RBIMPL_STDALIGN_H */
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