Diff below adds C11 support to the feature test macros in <sys/cdefs.h> and uses those to conditionally define the max_align_t type in <stddef.h>. All systems/compilers seem to use the same construct. See
https://reviews.llvm.org/rL201729 for a bit more background. This will make it possible to remove clang's private <stddef.h> without losing functionality. Since our base compiler doesn't have C11 support, the type generally won't be available. But it can be made available by using gcc -D_ISOC11_SOURCE With clang, C11 support is enabled by default, so max_align_t is visible. But it can be hidden by using clang -std=c99 I don't expect any major fall-out in ports from this. ok? Index: sys/sys/cdefs.h =================================================================== RCS file: /cvs/src/sys/sys/cdefs.h,v retrieving revision 1.39 diff -u -p -r1.39 cdefs.h --- sys/sys/cdefs.h 18 Apr 2014 11:51:17 -0000 1.39 +++ sys/sys/cdefs.h 5 Jan 2017 20:07:02 -0000 @@ -375,14 +375,19 @@ #endif /* - * _ISOC99_SOURCE and __STDC_VERSION__ override any of the other macros since - * they are non-exclusive. + * _ISOC99_SOURCE, _ISOC11_SOURCE and __STDC_VERSION__ override any of + * the other macros since they are non-exclusive. */ #if defined(_ISOC99_SOURCE) || \ (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901) || \ (defined(__cplusplus) && __cplusplus >= 201103) # undef __ISO_C_VISIBLE # define __ISO_C_VISIBLE 1999 +#endif +#if defined(_ISOC11_SOURCE) || \ + (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112) +# undef __ISO_C_VISIBLE +# define __ISO_C_VISIBLE 2011 #endif /* Index: include/stddef.h =================================================================== RCS file: /cvs/src/include/stddef.h,v retrieving revision 1.13 diff -u -p -r1.13 stddef.h --- include/stddef.h 9 Sep 2016 18:12:37 -0000 1.13 +++ include/stddef.h 5 Jan 2017 20:07:02 -0000 @@ -71,4 +71,11 @@ typedef __mbstate_t mbstate_t; #define offsetof(type, member) ((size_t)(&((type *)0)->member)) #endif +#if __ISO_C_VISIBLE >= 2011 +typedef struct { + long long __max_align_ll __aligned(__alignof__(long long)); + long double __max_align_ld __aligned(__alignof__(long double)); +} max_align_t; +#endif + #endif /* _STDDEF_H_ */
