On 2020-Feb-27, at 16:37, John Baldwin <jhb at FreeBSD.org> wrote: > On 2/27/20 2:45 PM, Mark Millard wrote: >> John Baldwin jhb at FreeBSD.org wrote on >> Thu Feb 27 16:55:01 UTC 2020: >> >>> On 2/27/20 7:30 AM, Warner Losh wrote: >>>> Author: imp >>>> Date: Thu Feb 27 15:30:13 2020 >>>> New Revision: 358392 >>>> URL: https://svnweb.freebsd.org/changeset/base/358392 >>>> >>>> Log: >>>> _Static_assert is to be preferred to CTASSERT. >>>> >>>> Document the existing prefernce that _Static_assert be used in preference >>>> to the >>>> old CTASSERT we used to use for compile time assertions. >>> >>> Actually, I think what we want to use is static_assert(). The intention in >>> userland C is that _Static_assert() is an internal keyword and <assert.h> >>> adds static_assert() as an alias, similar to <stdalign.h> defining alignas, >>> etc. I think what we should do for the kernel is have <sys/systm.h> define >>> map static_assert to _Static_assert and replace existing _Static_assert >>> usage with the proper spelling. >>> >> >> Be warned static_assert is a C++ keyword as of C++11. >> >> c++11 added: static_assert(bool_constexpr,message) >> c++17 added: static_assert(bool_constexpr) >> >> C11 added _Static_assert(expression,message) >> C2x gets _Static_assert(expression) >> >> C11 added "#define static_assert _Static_assert" to <assert.h> >> >> It makes for a bit of a mess in code to be allowed >> to be processed by both C and C++. >> >> The wording may need to specify enough to tell what to >> do for such code and the headers may need logic to >> cause that context to exist across both languages >> when the header is allowed for both. > > The intent of the C11 changes is to permit equivalent use of static_assert() > in both languages. The #define in <assert.h> is guarded to not kick in for > C++. Ahh. I had vague memories of past oddities in the area that I was involved in. So I looked and found (in head -r3578132 source) : # more /usr/src/sys/sys/cdefs.h . . . #if !__has_extension(c_static_assert) #if (defined(__cplusplus) && __cplusplus >= 201103L) || \ __has_extension(cxx_static_assert) #define _Static_assert(x, y) static_assert(x, y) #elif __GNUC_PREREQ__(4,6) && !defined(__cplusplus) /* Nothing, gcc 4.6 and higher has _Static_assert built-in */ #elif defined(__COUNTER__) #define _Static_assert(x, y) __Static_assert(x, __COUNTER__) #define __Static_assert(x, y) ___Static_assert(x, y) #define ___Static_assert(x, y) typedef char __assert_ ## y[(x) ? 1 : -1] \ __unused #else #define _Static_assert(x, y) struct __hack #endif #endif . . . # more /usr/include/assert.h . . . /* * Static assertions. In principle we could define static_assert for * C++ older than C++11, but this breaks if _Static_assert is * implemented as a macro. * * C++ template parameters may contain commas, even if not enclosed in * parentheses, causing the _Static_assert macro to be invoked with more * than two parameters. */ #if __ISO_C_VISIBLE >= 2011 && !defined(__cplusplus) #define static_assert _Static_assert #endif . . . So one can define a _Static_assert macro, sometimes in terms of static_assert, and the other sometimes defines a static_assert macro in terms of _Static_assert. Messy, but possibly localized. That prompted a more general grep: # grep -r "define[ _]*[Ss]tatic_assert" /usr/src/* | more /usr/src/contrib/llvm-project/libcxx/include/__config:# define static_assert(...) _Static_assert(__VA_ARGS__) /usr/src/contrib/llvm-project/libunwind/src/config.h: #define static_assert(__b, __m) \ /usr/src/include/assert.h: * Static assertions. In principle we could define static_assert for /usr/src/include/assert.h:#define static_assert _Static_assert /usr/src/sys/sys/cdefs.h:#define _Static_assert(x, y) static_assert(x, y) /usr/src/sys/sys/cdefs.h:#define _Static_assert(x, y) __Static_assert(x, __COUNTER__) /usr/src/sys/sys/cdefs.h:#define __Static_assert(x, y) ___Static_assert(x, y) /usr/src/sys/sys/cdefs.h:#define ___Static_assert(x, y) typedef char __assert_ ## y[(x) ? 1 : -1] \ /usr/src/sys/sys/cdefs.h:#define _Static_assert(x, y) struct __hack /usr/src/usr.bin/dtc/util.hh:#define static_assert(x, y) ((void)0) So not much else. === Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar) _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
Re: svn commit: r358392 - head/share/man/man9
Mark Millard via svn-src-head Thu, 27 Feb 2020 19:04:24 -0800
- svn commit: r358392 - head/share/man/man9 Warner Losh
- Re: svn commit: r358392 - head/share/ma... John Baldwin
- Re: svn commit: r358392 - head/share/ma... Mark Millard via svn-src-head
- Re: svn commit: r358392 - head/shar... John Baldwin
- Re: svn commit: r358392 - head/... Mark Millard via svn-src-head
- Re: svn commit: r358392 - h... Mark Millard via svn-src-head
- Re: svn commit: r35839... Warner Losh