From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7555 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: Re: [PATCH] generate debug_frame info for __syscall_cp_asm (i386) so gdb can get backtrace Date: Wed, 29 Apr 2015 11:57:03 -0400 Message-ID: <20150429155703.GV17573@brightrain.aerifal.cx> References: <20150429144618.GA12549@alex-ThinkPad-L530> 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 1430323041 5109 80.91.229.3 (29 Apr 2015 15:57:21 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2015 15:57:21 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-7568-gllmg-musl=m.gmane.org@lists.openwall.com Wed Apr 29 17:57:21 2015 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 1YnUMP-0007d5-Tk for gllmg-musl@m.gmane.org; Wed, 29 Apr 2015 17:57:18 +0200 Original-Received: (qmail 21693 invoked by uid 550); 29 Apr 2015 15:57:16 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 21672 invoked from network); 29 Apr 2015 15:57:15 -0000 Content-Disposition: inline In-Reply-To: <20150429144618.GA12549@alex-ThinkPad-L530> User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:7555 Archived-At: On Wed, Apr 29, 2015 at 04:46:18PM +0200, Alex Dowad wrote: > On Mon, 27 Apr 2015 16:57:22 -0400, Rich Felkner wrote: > > This has been requested before, but it really uglifies the asm and > > makes it unreadable. Do you have any ideas for mitigating the problem? > > Perhaps using PUSH() and POP() macros which automatically add .cfi_* > directives? The reason I don't like solutions like this is that anyone reading the code immediately wonders what those macros are and whether there is important functionality hidden in them that's obscuring what the code is doing. I know that's my first thought when I see asm (or C) written like that. Also this is rather x86-specific; many other archs don't have/use push/pop instructions. > > Another idea would be programmatically generating the cfi from the asm > > with a script that runs at compile-time, and passing the output of the > > script to the assembler. One benefit of this approach is that it could > > be tuned based on whether -g is in use or not. With hard-coded .cfi_* > > I don't see a clear way to suppress it when -g is not in use. > > Conditionally defining the PUSH() and POP() macros to omit the .cfi_* > stuff when debugging is disabled? > > Of course using a script to parse the asm is SO much more slick... but > you probably don't want to add too many dependencies to your build process > either. Would it have to be just a plain shell script? It would be either sed or awk most likely. Plain shell would work for writing it too but would probably be uglier, and sed is already required anyway for alltypes.h generation. If any new tool were required (unlikely) then configure would just detect its absence and turn off cfi generation for asm if it's missing/broken. Rich