Date: Thu, 22 Feb 2018 11:42:09 -0800 From: Eitan Adler <lists@eitanadler.com> To: Warner Losh <imp@bsdimp.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, FreeBSD Hackers <freebsd-hackers@freebsd.org>, Tijl Coosemans <tijl@freebsd.org>, FreeBSD Standards <freebsd-standards@freebsd.org>, Kevin Lo <kevlo@freebsd.org> Subject: Re: Marking select(2) as restrict Message-ID: <CAF6rxgn=-J5uAAG86zgV-vFiPpzgoFre-nBZ94EPPKz9eCX8Jg@mail.gmail.com> In-Reply-To: <CANCZdfrDCt6JCWcZDk8c3AdqX%2B1MwbUH2cNr=NqqyP7gWmUByg@mail.gmail.com> References: <CAF6rxg=h_oMiUu7P=GAOQf_OySQM2w31hg6Kas%2B3jeEM3qq_Cg@mail.gmail.com> <CAF6rxgnt9c0n8i-nHQwoKGbZKF2hM5AZqEJnz0CLo26XOO4_sg@mail.gmail.com> <20180221032247.GA81670@ns.kevlo.org> <CAF6rxg=WwqeBnmJzfOZgtwrYesXPfvJFeaVmQwtTa_89_sxaJg@mail.gmail.com> <CANCZdfo46bhfaRpbqOmJjk4%2B=1R2c5kvmrJPENaxNgK==5M4kg@mail.gmail.com> <CAF6rxg=wNVgDUF9o744ngmzPNeHB3hqdrLufy=yS3D4osczxFQ@mail.gmail.com> <20180221104400.GU94212@kib.kiev.ua> <20180222112752.10da7e51@kalimero.tijl.coosemans.org> <20180222105608.GE94212@kib.kiev.ua> <CANCZdfrDCt6JCWcZDk8c3AdqX%2B1MwbUH2cNr=NqqyP7gWmUByg@mail.gmail.com>
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On 22 February 2018 at 06:43, Warner Losh <imp@bsdimp.com> wrote: > On Thu, Feb 22, 2018 at 3:56 AM, Konstantin Belousov <kostikbel@gmail.com> > wrote: > >> On Thu, Feb 22, 2018 at 11:27:52AM +0100, Tijl Coosemans wrote: >> > On Wed, 21 Feb 2018 12:44:00 +0200 Konstantin Belousov < >> kostikbel@gmail.com> wrote: >> > > On Tue, Feb 20, 2018 at 10:14:05PM -0800, Eitan Adler wrote: >> > >> On 20 February 2018 at 21:19, Warner Losh <imp@bsdimp.com> wrote: >> > >>> Once upon a time, this would break a lot of code. Perhaps times have >> > >>> changed. >> > >> >> > >> I've seen very little code that this would break though some of it >> > >> certainly exists. >> > > You certainly seen very little code, but the question was about the >> > > existed code. >> > >> > FWIW, it seems that glibc uses restrict since 2000 so there's unlikely to >> > be much fallout: >> > https://sourceware.org/git/?p=glibc.git;a=blob;f=misc/sys/select.h >> > https://sourceware.org/git/?p=glibc.git;a=commitdiff;h= >> 98cbe360d947b59e7a5eda068581f4cfeb4b99b3 >> >> Clearly, nobody knowns. At least, glibc is used with gcc compilation, not >> with clang. >> >> Consider the recently changed devd code: >> select(n + 1, &fd, &fd, &fd); >> There, compiler can see that restrict is applied to arguments which are >> given same values. Since this leads to the self-contradicting statement >> fd != fd >> which cannot be true, compliler in its optimizing wisdom can assume that >> the code is never executing and remove it. I do not know whether clang >> actually makes such transformation, but it does not sound unfeasible >> looking at its other advances. >> > > If the compilers affirmatively fails when this happens Compilers cannot fail since errors are only detectable at runtime. The value of the exp-run is (a) ensuring that we don't break prototypes of some applications (b) exercising the applications as much as we can -- Eitan Adler
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