From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31308 invoked by alias); 19 Feb 2014 17:01:41 -0000 Mailing-List: contact gcc-help-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-help-owner@gcc.gnu.org Received: (qmail 31293 invoked by uid 89); 19 Feb 2014 17:01:41 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW,RP_MATCHES_RCVD,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mail-ob0-f173.google.com Received: from mail-ob0-f173.google.com (HELO mail-ob0-f173.google.com) (209.85.214.173) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-SHA encrypted) ESMTPS; Wed, 19 Feb 2014 17:01:40 +0000 Received: by mail-ob0-f173.google.com with SMTP id uz6so720164obc.4 for ; Wed, 19 Feb 2014 09:01:38 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc:content-type; bh=cGl6nJzIQxEX5vLg/SpZ2joESTxRR6VmZEYQZA1PscY=; b=WgUEP+xFcsM3lmHrmA7yJIYrq1Cetrf7PhGbHZcdq0tB9JCnbkU54zsE6kSMTdauO7 S6VXL3QXi9yn2RhFfA4x7JLh1gM/en+oYam/XOAE4F7owIzgsG0f09T6ig/0NaWPCI+z I24wFUKOtLev3poxtSkJY+TbUqrZFRyz/vbqVhNzX1nWjjeDRjhkXBBnBnT01w7fJKvM kRtpeA/981n2HKT1+NAGFAM48cH2CN34KrBFraj4+/j37rwYVPRPVzEdjyXJvSOc25Q/ H47kWRACOWcJweI0Wbudps+BQPlCyrawOwCwUpDCFnIdk5dNLb1moZoMqD4p0wGhodLA 0YSQ== X-Gm-Message-State: ALoCoQlXzgdRxfs01s4p2JVY+7cLCV4ShnT3f//Mozj96b94HuT2qzFqIEZV42hr8+Tgtolahvh0niiVhY+qWQAohNZoI+zIXNyUYdJ22velTi953F2JTAHer4v+q/wpIgjQEJj6CeoSG0c0hszUEP6+N4x6aZBr35AS+A8VvAtYN2dOxyMnh0eDhy4d6rXiFasFsQUAt5Y3 MIME-Version: 1.0 X-Received: by 10.60.70.239 with SMTP id p15mr31748033oeu.26.1392829298424; Wed, 19 Feb 2014 09:01:38 -0800 (PST) Received: by 10.60.39.2 with HTTP; Wed, 19 Feb 2014 09:01:38 -0800 (PST) In-Reply-To: References: Date: Wed, 19 Feb 2014 17:01:00 -0000 Message-ID: Subject: Re: Moving C++ code to a different ELF section From: Ian Lance Taylor To: Saul Tamari Cc: "gcc-help@gcc.gnu.org" Content-Type: text/plain; charset=UTF-8 X-IsSubscribed: yes X-SW-Source: 2014-02/txt/msg00110.txt.bz2 On Wed, Feb 19, 2014 at 7:15 AM, Saul Tamari wrote: > > I am trying to see if moving mostly unused code (e.g. conditional > debug print statements) to a different section (and to different > pages) would impact performance in a large application. So, you want -freorder-blocks-and-partition. You can't do it using asm statements that change the section in ways that the compiler doesn't know about. Ian > On Wed, Feb 19, 2014 at 9:11 AM, Ian Lance Taylor wrote: >> On Wed, Feb 19, 2014 at 5:57 AM, Saul Tamari wrote: >>> >>> I'm trying to move some C++ code to a different ELF section and am >>> facing some errors which I don't understand. I'm using g++ v4.8.1 on >>> x86. >>> >>> When compiling the following code I'm getting these errors: >>> /tmp/ccpp2AkE.s: Assembler messages: >>> /tmp/ccpp2AkE.s:63: Error: CFI instruction used without previous .cfi_startproc >>> /tmp/ccpp2AkE.s:64: Error: CFI instruction used without previous .cfi_startproc >>> /tmp/ccpp2AkE.s:66: Error: .cfi_endproc without corresponding .cfi_startproc >>> /tmp/ccpp2AkE.s: Error: open CFI at the end of file; missing >>> .cfi_endproc directive >>> >>> >>> The source is: >>> #include >>> #include >>> >>> int qqq; >>> >>> int main(int argc, char* argv[]) >>> { >>> std::cout << "hey " << std::endl; >>> >>> qqq = rand(); >>> if (qqq > 0x1000000) { >>> asm volatile ("jmp 1f \n\t .pushsection >>> __kuku,\"ax\",@progbits \n\t 1:"); >>> std::cout << "0x123456" << std::endl; >>> throw 12345; >>> asm volatile("jmp 3f \n\t .popsection \n\t 3:"); >>> } >>> >>> return 0; >>> } >>> >>> >>> What do these errors mean? Is there a way to fix them? Is there an >>> alternate method to move similar code to a different section? >> >> The assembler errors occur because GCC emits debug info in the >> assembler stream using CFI pseudo-ops, and you are moving the >> pseudo-ops to a different section in a way that GCC does not >> understand. The assembler is seeing CFI pseudo-ops that make no >> sense, so it is giving errors about them. >> >> The approach you are using can not work. The compiler is not an >> assembler. It does not issue instructions in precise sequence. It >> copies and duplicates and rearranges instructions as it sees fit. >> This is so even though you are using asm volatile. All the asm >> volatile promises is that the string will appear at the right point in >> execution sequence. Your strings can only work if they appear at the >> right point in the assembler output. That is a different matter that >> the compiler does not guarantee. >> >> You didn't see what you are trying to do, but at a guess you should >> look at the -freorder-blocks-and-partition option. >> >> Ian