From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/9490 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: FreeBSD's Google Summer of Code 2016 Date: Sat, 5 Mar 2016 19:25:47 -0500 Message-ID: <20160306002547.GM9349@brightrain.aerifal.cx> References: <56DB3D70.8010601@FreeBSD.org> <20160305212517.GK9349@brightrain.aerifal.cx> <56DB6095.4060204@FreeBSD.org> <20160305233254.GL9349@brightrain.aerifal.cx> <56DB766A.3050500@FreeBSD.org> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1457223966 17087 80.91.229.3 (6 Mar 2016 00:26:06 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 6 Mar 2016 00:26:06 +0000 (UTC) Cc: musl@lists.openwall.com To: Pedro Giffuni Original-X-From: musl-return-9503-gllmg-musl=m.gmane.org@lists.openwall.com Sun Mar 06 01:26:05 2016 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1acMWK-0008PK-AA for gllmg-musl@m.gmane.org; Sun, 06 Mar 2016 01:26:04 +0100 Original-Received: (qmail 17763 invoked by uid 550); 6 Mar 2016 00:26:02 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 17738 invoked from network); 6 Mar 2016 00:26:01 -0000 Content-Disposition: inline In-Reply-To: <56DB766A.3050500@FreeBSD.org> User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:9490 Archived-At: On Sat, Mar 05, 2016 at 07:14:34PM -0500, Pedro Giffuni wrote: > > > On 03/05/16 18:32, Rich Felker wrote: > >On Sat, Mar 05, 2016 at 05:41:25PM -0500, Pedro Giffuni wrote: > >>First of all, great to hear there is interest on the musl side too. > >> > >>I think the biggest precedent of porting linux-oriented C libraries > >>came from Debian's kFreeBSD. We accomodated a little by for them > >>by defining __FreeBSD_kernel__ in sys/param.h. > >> > >>While using the optional linux-abi futex in FreeBSD could be an option, > >>it is not really the cleanest option. The Debian guys did a port of > >>NPTL using regular pthreads: > >> > > Of course I ahould have meant "based on regular FreeBSD kernel services". > > >>http://thread.gmane.org/gmane.linux.debian.ports.bsd/11702 > >> > >>I am certain this will require more research but it would be useful > >>for other ports as well. > > > > We could ask Petr Salinger for the details, but I am pretty sure > FreeBSD has the required functionality natively. > > >Glibc/NPTL has a lot of what I'd call "gratuitous abstraction" (like > >the lll stuff) in their pthread primitives which makes this > >"possible". I call it gratuitous because it's really really hard to > >achieve correct implementations of the pthread sync primitives that > >don't have serious corner-case bugs, and it's unlikely that their > >abstractions actually suffice to make correct alternate > >implementations. > > > >musl does not have any such abstraction. We require a compare-and-swap > >operation or equivalent on which arbitrary atomic operations can be > >constructed, a futex or equivalent operation that's roughly > >while(*addr==expected) sleep(), and implement all the sync primitives > >just once on top of these. > > > > I am not a threading expert (or even a CS guy), but it sounds like > mutex(9) with condvar(9) would do [1]: No, they don't satisfy the needs of musl; they have their own additional storage requirements and are probably not AS-safe. It might be possible to use them to implement a userspace-emulated futex queue (only if they are AS-safe), but I don't see a way to extend that to the process-shared case. Rich