Date: Wed, 3 May 2017 15:07:43 -0600 From: Alan Somers <asomers@freebsd.org> To: Bruce Evans <brde@optusnet.com.au> Cc: Eric van Gyzen <eric@vangyzen.net>, Warner Losh <imp@bsdimp.com>, Ngie Cooper <yaneurabeya@gmail.com>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r317755 - head/sbin/ifconfig Message-ID: <CAOtMX2gi0q4FiHKWUWK8bwtViKFscvCRrsaGKAkw6%2BbrSqYWMw@mail.gmail.com> In-Reply-To: <20170504062448.U1383@besplex.bde.org> References: <201705031721.v43HL2vS071819@repo.freebsd.org> <8EA7A2E9-A429-4DC2-85CE-1B5AAEDF86FD@gmail.com> <CAOtMX2hbiXAna_UxMonf1Drqx3PkzW2%2BToezai%2BQ32VYq_DXSg@mail.gmail.com> <CANCZdfpgUif9STteK=W3Pr0D9UqkPqU9edZqXLfLyoD5d=UPag@mail.gmail.com> <CAOtMX2iC9dqBmWHGODA%2BMg8caxeKP%2BtEGzGdXD48QaB0a9U5UQ@mail.gmail.com> <e93b38b5-6d1b-b463-ab50-b3f9ac2c4a17@vangyzen.net> <20170504062448.U1383@besplex.bde.org>
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On Wed, May 3, 2017 at 2:51 PM, Bruce Evans <brde@optusnet.com.au> wrote: > On Wed, 3 May 2017, Eric van Gyzen wrote: > >> On 05/03/2017 14:38, Alan Somers wrote: >>> >>> On Wed, May 3, 2017 at 1:34 PM, Warner Losh <imp@bsdimp.com> wrote: >>>> >>>> On Wed, May 3, 2017 at 1:32 PM, Alan Somers <asomers@freebsd.org> wrote: >>>>> >>>>> On Wed, May 3, 2017 at 12:16 PM, Ngie Cooper <yaneurabeya@gmail.com> >>>>> wrote: >>>>>> >>>>>> >>>>>>> On May 3, 2017, at 10:21, Alan Somers <asomers@FreeBSD.org> wrote: >>>>>>> >>>>>>> Author: asomers >>>>>>> Date: Wed May 3 17:21:01 2017 >>>>>>> New Revision: 317755 >>>>>>> URL: https://svnweb.freebsd.org/changeset/base/317755 >>>>>>> >>>>>>> Log: >>>>>>> Various Coverity fixes in ifconfig(8) >>>>>> >>>>>> >>>>>> ... >>>>>> >>>>>>> * Mark usage() as _Noreturn (1305806, 1305750) >>>>>> >>>>>> >>>>>> ... >>>>>> >>>>>>> -static void usage(void); >>>>>>> +static void usage(void) _Noreturn; >>>>>> >>>>>> >>>>>> Hi Alan, >>>>>> Please use __dead2 instead to be consistent with legacy use of >>>>>> similar gcc attributes. >>>>>> Thanks, >>>>>> -Ngie >>>>> >>>>> >>>>> Why not use _Noreturn? It's standardized by C11, so tools understand >>>>> it better than __dead2. >>>> >>>> >>>> Tools that can't understand #define __dead2 _Noreturn aren't worth >>>> supporting. >>> >>> Some tools don't expand preprocessor macros. Like my editor, for >>> example, which highlights _Noreturn as a keyword but not __dead2. >> >> >> Please use _Noreturn, because it's standard. sys/cdefs.h already >> defines it appropriately for C < C11. > > > _Noreturn is far too hard to use. The above use of it is a syntax error: > > pts/12:bde@freefall:~/u3> cat z.c > void foo(void) _Noreturn; > _Noreturn void foo(void); > pts/12:bde@freefall:~/u3> cc -std=c11 z.c > z.c:1:16: error: '_Noreturn' keyword must precede function declarator > void foo(void) _Noreturn; > ^~~~~~~~~ > _Noreturn > 1 error generated. > > sys/cdefs.h defines might define it appropropriately for C < C11, but > it defines it as __dead2 for all C, so prevents the C11 _Noreturn > keyword being used. This normally breaks detection of the syntax error. > Normally <sys/cdefs.h> is included first, so you __dead2 obfuscated by > spelling it _Noreturn instead of C11 _Noreturn. > > Defining _Noreturn as __dead2 is wrong because it gives the opposite > syntax error. __dead2 can now be placed anywhere, but everything in > sys/cdefs.h is supposed to be portable back to gcc-1. __dead2 must > be placed after the function for gcc-2.0, since __attribute__(()) had > more restrictions then. So if you write: > > #include <sys/cdefs.h> > _Noreturn void foo(void); > > to satisfy the C11 syntax, then you get a syntax error for old gcc (> 1). > > This is just the start of the complications for soft-coded C11'isms. > C11 also has noreturn. You have to include <stdnoreturn.h> to get that. > But you actiually get the _Noreturn macro which expands to __dead2. > > There are further complications for C++11. sys/cdefs.h does have a > correct-looking ifdef for C+11. This gives the [[noreturn]] keyward > instead of __dead2. C11 doesn't have <stdnoreturn.h>. I think its > keyword must be spelled [[noreturn]]. This spelling is completely > incompatibly with C. > > Bruce Why do you say that cdefs.h should be compatible with gcc-1? gcc-2 was released more than 25 years ago. gcc-1 isn't the default compiler for any architecture and isn't available in ports. If anybody can find a copy of gcc-1, I doubt that much of our codebase would compile. It sounds to me that the best practice would be to place both __dead2 and _Noreturn before the function name. -Alan
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