Date: Thu, 27 Feb 2020 20:17:39 -0800 From: Mark Millard <marklmi@yahoo.com> To: John Baldwin <jhb@FreeBSD.org> Cc: svn-src-head@freebsd.org, Warner Losh <imp@bsdimp.com> Subject: Re: svn commit: r358392 - head/share/man/man9 Message-ID: <45DC452F-C753-46D7-A071-0B231F6F6206@yahoo.com> In-Reply-To: <DE283429-4303-4929-96A6-8EF43BDF8F17@yahoo.com> References: <217D39BA-4FDC-490C-8490-533D244E79CE.ref@yahoo.com> <217D39BA-4FDC-490C-8490-533D244E79CE@yahoo.com> <59374055-922a-81f1-1b05-a572e1cb6b1a@FreeBSD.org> <DE283429-4303-4929-96A6-8EF43BDF8F17@yahoo.com>
next in thread | previous in thread | raw e-mail | index | archive | help
[Ignoring llvm-project and libstdc++, I only find about 24 other instances of "static_assert".] On 2020-Feb-27, at 19:03, Mark Millard <marklmi at yahoo.com> wrote > On 2020-Feb-27, at 16:37, John Baldwin <jhb at FreeBSD.org> wrote: >=20 >> 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: >>>=20 >>>> 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 >>>>>=20 >>>>> Log: >>>>> _Static_assert is to be preferred to CTASSERT. >>>>>=20 >>>>> Document the existing prefernce that _Static_assert be used in = preference to the >>>>> old CTASSERT we used to use for compile time assertions. >>>>=20 >>>> 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. >>>>=20 >>>=20 >>> Be warned static_assert is a C++ keyword as of C++11. >>>=20 >>> c++11 added: static_assert(bool_constexpr,message) >>> c++17 added: static_assert(bool_constexpr) >>>=20 >>> C11 added _Static_assert(expression,message) >>> C2x gets _Static_assert(expression) >>>=20 >>> C11 added "#define static_assert _Static_assert" to <assert.h> >>>=20 >>> It makes for a bit of a mess in code to be allowed >>> to be processed by both C and C++. >>>=20 >>> 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. >>=20 >> 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++. >=20 > 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) : >=20 > # more /usr/src/sys/sys/cdefs.h > . . . > #if !__has_extension(c_static_assert) > #if (defined(__cplusplus) && __cplusplus >=3D 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 > . . . >=20 > # 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 >=3D 2011 && !defined(__cplusplus) > #define static_assert _Static_assert > #endif > . . . >=20 > 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. >=20 > Messy, but possibly localized. >=20 > That prompted a more general grep: >=20 > # 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) >=20 > So not much else. Just an FYI: Looks like static_assert is little used (outside llvm-project and libstdc++): # grep -r "\<static_assert\>" /usr/src/* | grep -v llvm-project | grep = -v "libstdc\+\+" | more /usr/src/contrib/googletest/googlemock/include/gmock/gmock-matchers.h: = static_assert( /usr/src/contrib/googletest/googlemock/include/gmock/gmock-matchers.h: = static_assert(sizeof...(Args) > 0, "Must have at least one matcher."); /usr/src/contrib/googletest/googlemock/docs/DesignDoc.md:Google Test = (the name is chosen to match `static_assert` in C++0x). = /usr/src/contrib/googletest/googletest/include/gtest/internal/gtest-port.h= :# define GTEST_COMPILE_ASSERT_(expr, msg) static_assert(expr, #msg) = /usr/src/contrib/googletest/googletest/include/gtest/internal/gtest-port.h= :// (In C++11, we simply use static_assert instead of the following) /usr/src/contrib/bsnmp/snmpd/trans_inet.c:static_assert(offsetof(struct = port_sock, input) =3D=3D 0, /usr/src/contrib/bsnmp/snmpd/trans_inet.c:static_assert(offsetof(struct = inet_port, tport) =3D=3D 0, /usr/src/contrib/libcxxrt/guard.cc:static_assert(sizeof(guard_t) =3D=3D = sizeof(uint64_t), ""); /usr/src/contrib/ofed/libibumad/umad.c:static_assert(sizeof(struct = ib_user_mad_reg_req) =3D=3D IOCPARM_LEN(IB_USER_MAD_REGISTER_AGENT), /usr/src/contrib/ofed/libibumad/umad.c:static_assert(sizeof(struct = ib_user_mad_reg_req2) =3D=3D IOCPARM_LEN(IB_USER_MAD_REGISTER_AGENT2), /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/contrib/zstd/contrib/pzstd/utils/FileSystem.h: = static_assert(false, "No POSIX stat() support."); /usr/src/sys/contrib/zstd/contrib/pzstd/utils/FileSystem.h: = static_assert(false, "NO POSIX stat() support."); /usr/src/usr.bin/dtc/HACKING:The code also makes use of = `static_assert()` to track compile-time invariants. /usr/src/usr.bin/dtc/util.hh:#ifndef static_assert /usr/src/usr.bin/dtc/util.hh:#define static_assert(x, y) ((void)0) /usr/src/usr.bin/dtc/util.hh: static_assert(sizeof(T) > 1, /usr/src/usr.sbin/bhyve/task_switch.c:static_assert(sizeof(struct tss32) = =3D=3D 104, "compile-time assertion failed"); /usr/src/usr.sbin/bhyve/pci_emul.h:static_assert(sizeof(struct msicap) = =3D=3D 14, "compile-time assertion failed"); /usr/src/usr.sbin/bhyve/pci_emul.h:static_assert(sizeof(struct msixcap) = =3D=3D 12, "compile-time assertion failed"); /usr/src/usr.sbin/bhyve/pci_emul.h:static_assert(sizeof(struct pciecap) = =3D=3D 60, "compile-time assertion failed"); /usr/src/usr.sbin/syslogd/syslogd.c: = static_assert(sizeof(f->f_prevline) =3D=3D sizeof(saved), _Static_assert looks to be far more common. (Too long to list here.) =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?45DC452F-C753-46D7-A071-0B231F6F6206>