From owner-freebsd-hackers@FreeBSD.ORG Mon Apr 21 12:02:25 2008 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id F19171065671 for ; Mon, 21 Apr 2008 12:02:25 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from harmony.bsdimp.com (bsdimp.com [199.45.160.85]) by mx1.freebsd.org (Postfix) with ESMTP id B1F828FC1E for ; Mon, 21 Apr 2008 12:02:25 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from localhost (localhost [127.0.0.1]) by harmony.bsdimp.com (8.14.2/8.14.1) with ESMTP id m3LC05hI027208; Mon, 21 Apr 2008 06:00:06 -0600 (MDT) (envelope-from imp@bsdimp.com) Date: Mon, 21 Apr 2008 06:01:07 -0600 (MDT) Message-Id: <20080421.060107.1079619394.imp@bsdimp.com> To: ertr1013@student.uu.se From: "M. Warner Losh" In-Reply-To: <20080421070050.GA13685@owl.midgard.homeip.net> References: <20080420103910.GA92852@owl.midgard.homeip.net> <20080420.232432.-1175574853.imp@bsdimp.com> <20080421070050.GA13685@owl.midgard.homeip.net> X-Mailer: Mew version 5.2 on Emacs 21.3 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: emily.bckr@gmail.com, freebsd-hackers@freebsd.org Subject: Re: symbol table X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Apr 2008 12:02:26 -0000 In message: <20080421070050.GA13685@owl.midgard.homeip.net> Erik Trulsson writes: : On Sun, Apr 20, 2008 at 11:24:32PM -0600, M. Warner Losh wrote: : > In message: <20080420103910.GA92852@owl.midgard.homeip.net> : > Erik Trulsson writes: : > : On Sun, Apr 20, 2008 at 12:02:09PM +0300, emily becker wrote: : > : > Hi, : > : > : > : > I have a question about symbol table. : > : > One of the section In symbol table is memory adress which symbol is located. : > : > I wonder if this memory adress is bound at run-time or compile-time? : > : : > : It depends. Symbols referring to objects in a dynamically loaded library : > : will be bound at run-time, the rest should be bound at compile-time. : > : > They are bound at link-time, not compile-time. This is splitting a : > fine hair, but compile-time is when a .o or .so is created, while link : > time combines .o-like things together into a bigger thing. : : Well, I consider linking to be part of the compilation process so for : me link-time is a subset of compile-time. : You are however completely correct that it is at link-time that the binding : happens (for those symbols that can be resolved at link-time anyway.) While you might consider them the same, these are very important differences that need to be taken into account. A compile-time constant, for example, can be used to size an automatic array. A link-time or run-time constant cannot without gcc's extensions (magic tricks can be played to make link-time constants size certain global objects, but then sizeof() those objects fail). The terminology is well worn, and matters in some contexts, so I tend to be a stickler here... Warner