From e9fb2bc873a55181ac7d581e7252db3754a3209d Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=E5=8D=9C=E9=83=A8=E6=98=8C=E5=B9=B3?= Date: Wed, 23 Sep 2020 10:57:35 +0900 Subject: 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. --- configure.ac | 58 +++++++++++++++++--------- include/ruby/internal/stdalign.h | 90 ++++++++++++++++++++++------------------ 2 files changed, 87 insertions(+), 61 deletions(-) diff --git a/configure.ac b/configure.ac index 46fdecda23..f7bbc36366 100644 --- a/configure.ac +++ b/configure.ac @@ -1460,26 +1460,44 @@ AS_IF([test "$rb_cv_va_args_macro" = yes], [ AC_DEFINE(HAVE_VA_ARGS_MACRO) ]) -AC_CACHE_CHECK([for alignof() syntax], rb_cv_have_alignof,[ -rb_cv_have_alignof=no -# Prefer alignof over _Alignof to allow C++ compiler to read ruby.h -RUBY_WERROR_FLAG([ -for expr in \ - "alignof" \ - "_Alignof" \ - "__alignof" \ - "__alignof__" \ -; -do - AC_TRY_COMPILE([ - @%:@ifdef HAVE_STDALIGN_H - @%:@include - @%:@endif],[return (int)$expr(int);], - [rb_cv_have_alignof="$expr"; break], []) -done -])]) -AS_IF([test "$rb_cv_have_alignof" != no], [ - AC_DEFINE_UNQUOTED(RUBY_ALIGNOF, $rb_cv_have_alignof) +# We want C11's `_Alignof`. GCC (and alike) have `__alignof__`, which behave +# slightly differently than the C11's. We cannot use `__alignof__` for our +# purpose. The problem is, however, that old gcc and old clang had both +# implemented `_Alignof` as a synonym of `__alignof__`. They are not what we +# want. We have to check sanity. +# +# See also: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023 +# See also: https://bugs.llvm.org/show_bug.cgi?id=26547 +AC_CACHE_CHECK([if _Alignof() works], rb_cv_have__alignof,[ + rb_cv_have__alignof=no + RUBY_WERROR_FLAG([ + AC_TRY_COMPILE([ + @%:@ifdef HAVE_STDALIGN_H + @%:@include + @%:@endif + @%:@ifdef STDC_HEADERS + @%:@include + @%:@endif + @%:@ifndef __GNUC__ + @%:@define __extension__ + @%:@endif + ], [ + typedef struct conftest_tag { + char _; + double d; + } T; + static int conftest_ary@<:@ + offsetof(T, d) == __extension__ _Alignof(double) + ? 1 : -1 + @:>@; + return conftest_ary@<:@0@:>@; + ], [ + rb_cv_have__alignof=yes + ]) + ]) +]) +AS_IF([test "$rb_cv_have__alignof" != no], [ + AC_DEFINE(HAVE__ALIGNOF) ]) RUBY_FUNC_ATTRIBUTE(__const__, CONSTFUNC) diff --git a/include/ruby/internal/stdalign.h b/include/ruby/internal/stdalign.h index 8c56fbbd69..8d9a0d21e0 100644 --- a/include/ruby/internal/stdalign.h +++ b/include/ruby/internal/stdalign.h @@ -22,16 +22,19 @@ */ #include "ruby/internal/config.h" -#ifdef HAVE_STDALIGN_H -# include +#ifdef STDC_HEADERS +# include #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 - -#elif defined(__cplusplus) && (__cplusplus >= 201103L) -# define RBIMPL_ALIGNOF alignof - -#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 +#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) +# /* 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() + +namespace ruby { +template +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 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 */ -- cgit v1.2.3