From owner-freebsd-current@FreeBSD.ORG Thu Mar 10 18:29:55 2011 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id ADD04106566C; Thu, 10 Mar 2011 18:29:55 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id 834CE8FC0A; Thu, 10 Mar 2011 18:29:55 +0000 (UTC) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id 34CEA46B98; Thu, 10 Mar 2011 13:29:55 -0500 (EST) Received: from jhbbsd.localnet (unknown [209.249.190.10]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id C214F8A01B; Thu, 10 Mar 2011 13:29:54 -0500 (EST) From: John Baldwin To: Matthew Fleming Date: Thu, 10 Mar 2011 13:29:53 -0500 User-Agent: KMail/1.13.5 (FreeBSD/7.4-CBSD-20110107; KDE/4.4.5; amd64; ; ) References: <20110308173909.GA71091@freebsd.org> <20110310163732.GA38320@freebsd.org> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201103101329.54044.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.6 (bigwig.baldwin.cx); Thu, 10 Mar 2011 13:29:54 -0500 (EST) Cc: Roman Divacky , freebsd-current@freebsd.org, Dimitry Andric Subject: Re: [TESTING]: one more boot2 shrinking patch X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 10 Mar 2011 18:29:55 -0000 On Thursday, March 10, 2011 11:58:30 am Matthew Fleming wrote: > On Thu, Mar 10, 2011 at 8:37 AM, Roman Divacky wrote: > > On Thu, Mar 10, 2011 at 09:20:58AM -0500, John Baldwin wrote: > >> On Wednesday, March 09, 2011 6:24:36 pm Dimitry Andric wrote: > >> > On 2011-03-09 14:23, John Baldwin wrote: > >> > >> gcc nor clang emits any code to initialize static type foo = 0; > >> > >> because it's expected that BSS is zeroed, which is not the case > >> > >> in boot2 so we have to initialize that explicitly > >> > > It used to be that if you explicitly initialized a variable to 0, it was > >> > > initialized to 0 in .data, but now gcc and clang recognize it is set to 0 and > >> > > move it to .bss. There appears to be no way to turn this feature off, > >> > > >> > Yes, there is; both gcc and clang have this option to turn it off: > >> > > >> > -fno-zero-initialized-in-bss > >> > If the target supports a BSS section, GCC by default puts variables > >> > that are initialized to zero into BSS. This can save space in the > >> > resulting code. > >> > > >> > This option turns off this behavior because some programs > >> > explicitly rely on variables going to the data section. E.g., so > >> > that the resulting executable can find the beginning of that > >> > section and/or make assumptions based on that. > >> > > >> > The default is -fzero-initialized-in-bss. > >> > >> Hah, that is better then. Thanks! I should have searched about this more > >> myself. :( Roman, can you try reverting the kname changes and adding this > >> to CFLAGS instead for both compilers? > > > > when I put -fno-zero-initialized-in-bss clang does not fit by 1.7K and > > gcc by 0.5K, we dont want this :) > > If there's that many variables explicitly initialized to zero, does > boot2 then need to explicitly bzero all of bss, not just kname, since > it's not handled by the loader? Otherwise it sounds like either > there's a lot of explicitly initialized variables that didn't need to > be, or there's a lot of potential for uninitialized variable nonsense > to happen. Yes. It would be good to see which symbols move from .bss to .data with this change. Hopefully the compilers aren't putting everything into .data. -- John Baldwin