From owner-freebsd-threads@FreeBSD.ORG Mon Mar 29 15:18:33 2004 Return-Path: Delivered-To: freebsd-threads@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id EBC6316A4D1 for ; Mon, 29 Mar 2004 15:18:33 -0800 (PST) Received: from daintree.corp.yahoo.com (daintree.corp.yahoo.com [216.145.52.172]) by mx1.FreeBSD.org (Postfix) with ESMTP id DF5ED43D1F for ; Mon, 29 Mar 2004 15:18:33 -0800 (PST) (envelope-from peter@yahoo-inc.com) Received: by daintree.corp.yahoo.com (Postfix, from userid 2154) id D4D03881F; Mon, 29 Mar 2004 15:18:33 -0800 (PST) From: Peter Wemm To: freebsd-threads@freebsd.org Date: Mon, 29 Mar 2004 15:18:33 -0800 User-Agent: KMail/1.6.1 References: In-Reply-To: MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200403291518.33559.peter@wemm.org> Subject: Re: Thread Local Storage X-BeenThere: freebsd-threads@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Threading on FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 29 Mar 2004 23:18:34 -0000 On Monday 29 March 2004 02:36 pm, Daniel Eischen wrote: [..] > > > > You don't need a syscall at thread switch if you do something > > > > like: > > > > > > > > _thread_switch(...) > > > > { > > > > if (tcb doesn't have LDT entry) { > > > > if (!free LDT entries) > > > > steal LDT entry from non-running thread; > > > > allocate LDT entry and point it at TLS goop for tcb. > > > > } > > > > load_gs(tcb's LDT sel); > > > > > > That's a system call on amd64. > > > > I'm not quite up to speed on amd64. So in 64-bit mode it doesn't > > really have an LDT at all, is that right? > > I'm not sure, but you have to make a system call to set it > or it's equivalent (amd64_set_fsbase()). Correct. There are two ways to do these things on this cpu. One is to use descriptor tables. The catch is that using descriptor tables forces a 4GB limit. It won't wrap around. The other way is to write to the MSRs for fsbase/gsbase. But the downside of that is that is a priviliged operation and needs to be done in supervisor mode. I don't *have* an LDT on the amd64 kernel. I'm dreading having to emulate the i386 sysarch LDT stuff already. -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5