From: Paul Eggert Date: Thu, 2 Apr 2015 17:35:53 +0000 (-0700) Subject: stddef: port to pre-C11 GCC on x86 X-Git-Tag: v1.0~7108 X-Git-Url: https://gitweb.git.savannah.gnu.org/gitweb/?a=commitdiff_plain;h=e2e66692cd072a39ce26ecf94117f934008aab24;p=gnulib.git stddef: port to pre-C11 GCC on x86 On this platform, max_align_t should have an alignment of 8 even though the storage alignments of double, long, etc. max out at 4. Inspired by a comment of Andreas Schwab's here: https://sourceware.org/ml/libc-alpha/2015-04/msg00017.html * lib/stddef.in.h (_GL_STDDEF_ALIGNAS) [!HAVE_MAX_ALIGN_T]: New macro. (max_align_t) [!HAVE_MAX_ALIGN_T]: Use it. * tests/test-stddef.c: Test __alignof__ too, if available. --- diff --git a/ChangeLog b/ChangeLog index 41dd857bad..6d690cc1a2 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,14 @@ +2015-04-02 Paul Eggert + + stddef: port to pre-C11 GCC on x86 + On this platform, max_align_t should have an alignment of 8 even + though the storage alignments of double, long, etc. max out at 4. + Inspired by a comment of Andreas Schwab's here: + https://sourceware.org/ml/libc-alpha/2015-04/msg00017.html + * lib/stddef.in.h (_GL_STDDEF_ALIGNAS) [!HAVE_MAX_ALIGN_T]: New macro. + (max_align_t) [!HAVE_MAX_ALIGN_T]: Use it. + * tests/test-stddef.c: Test __alignof__ too, if available. + 2015-03-24 Pádraig Brady quotearg-simple-tests: add missing gl_FUNC_MMAP_ANON dependency diff --git a/lib/stddef.in.h b/lib/stddef.in.h index 535132a4e2..d6b81fac82 100644 --- a/lib/stddef.in.h +++ b/lib/stddef.in.h @@ -83,12 +83,23 @@ /* Some platforms lack max_align_t. */ #if !@HAVE_MAX_ALIGN_T@ +/* On the x86, the maximum storage alignment of double, long, etc. is 4, + but GCC's C11 ABI for x86 says that max_align_t has an alignment of 8, + and the C11 standard allows this. Work around this problem by + using __alignof__ (which returns 8 for double) rather than _Alignof + (which returns 4), and align each union member accordingly. */ +# ifdef __GNUC__ +# define _GL_STDDEF_ALIGNAS(type) \ + __attribute__ ((__aligned__ (__alignof__ (type)))) +# else +# define _GL_STDDEF_ALIGNAS(type) /* */ +# endif typedef union { - char *__p; - double __d; - long double __ld; - long int __i; + char *__p _GL_STDDEF_ALIGNAS (char *); + double __d _GL_STDDEF_ALIGNAS (double); + long double __ld _GL_STDDEF_ALIGNAS (long double); + long int __i _GL_STDDEF_ALIGNAS (long int); } max_align_t; #endif diff --git a/tests/test-stddef.c b/tests/test-stddef.c index 317949655e..aa6ae549cc 100644 --- a/tests/test-stddef.c +++ b/tests/test-stddef.c @@ -55,6 +55,16 @@ verify (alignof (ptrdiff_t) <= alignof (max_align_t)); verify (alignof (size_t) <= alignof (max_align_t)); verify (alignof (wchar_t) <= alignof (max_align_t)); verify (alignof (struct d) <= alignof (max_align_t)); +#if defined __GNUC__ || defined __IBM__ALIGNOF__ +verify (__alignof__ (double) <= __alignof__ (max_align_t)); +verify (__alignof__ (int) <= __alignof__ (max_align_t)); +verify (__alignof__ (long double) <= __alignof__ (max_align_t)); +verify (__alignof__ (long int) <= __alignof__ (max_align_t)); +verify (__alignof__ (ptrdiff_t) <= __alignof__ (max_align_t)); +verify (__alignof__ (size_t) <= __alignof__ (max_align_t)); +verify (__alignof__ (wchar_t) <= __alignof__ (max_align_t)); +verify (__alignof__ (struct d) <= __alignof__ (max_align_t)); +#endif int main (void)