From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 22560 invoked by alias); 12 Oct 2002 17:55:13 -0000 Mailing-List: contact gdb-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sources.redhat.com Received: (qmail 22550 invoked from network); 12 Oct 2002 17:55:12 -0000 Received: from unknown (HELO crack.them.org) (65.125.64.184) by sources.redhat.com with SMTP; 12 Oct 2002 17:55:12 -0000 Received: from nevyn.them.org ([66.93.61.169] ident=mail) by crack.them.org with asmtp (Exim 3.12 #1 (Debian)) id 180RPZ-0002Tg-00; Sat, 12 Oct 2002 13:54:53 -0500 Received: from drow by nevyn.them.org with local (Exim 3.35 #1 (Debian)) id 180QTk-0004kR-00; Sat, 12 Oct 2002 13:55:08 -0400 Date: Sat, 12 Oct 2002 10:55:00 -0000 From: Daniel Jacobowitz To: Mark Kettenis Cc: gdb@sources.redhat.com Subject: Re: i386-linux signal backtraces broken Message-ID: <20021012175507.GA18048@nevyn.them.org> Mail-Followup-To: Mark Kettenis , gdb@sources.redhat.com References: <20021010184739.GA15971@nevyn.them.org> <863crbpmvl.fsf@elgar.kettenis.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <863crbpmvl.fsf@elgar.kettenis.dyndns.org> User-Agent: Mutt/1.5.1i X-SW-Source: 2002-10/txt/msg00112.txt.bz2 On Sat, Oct 12, 2002 at 07:50:38PM +0200, Mark Kettenis wrote: > Daniel Jacobowitz writes: > > > There's only one problem here. On my desktop (Debian GNU/Linux, glibc > > 2.2.5), there are two copies of sigaction in a dynamically linked > > executable. One of them's in libc.so.6 and the other is in ld-linux.so.2. > > The only __restore symbol we find is in ld-linux.so.2; this seems to be > > because we leave a symbol table in ld-linux.so.2 (probably for the > > debugger's benefit, so that it can find _dl_debug_state) - but we strip > > libc.so.6. > > How unfortunate. I'd recommend using an unstripped libc.so.6 when > doing any serious debugging, but I guess that won't trick the Debian > folks into distributing an unstripped libc. Never happen, I think. > > Unfortunately, the application gets the copy of __restore that is in > > libc.so.6. Which is right after a function whose name appears in the > > dynamic symbol table (sigaction). So it's considered to be part of > > sigaction, and NAME is "sigaction". > > > > We have two choices, that I see: > > - Call the code inspection functions always > > - Call the code inspection functions if the name is sigaction, taking > > advantage of the glibc implementation detail that sigaction is the > > only exported name for this function that I can see, and they are > > implemented right after it in the same file. > > We could also modify glibc such that __restore and __restore_rt get > included in libc.so's dynamic symbol table. Or perhaps we could > modify GDB such that it scans libc.so.6 for signal trampolines when it > is loaded. I don't like the former very much; then we'll require a newer libc for this to work. The latter would work... > > Option (A) is a performance hit. Option (B) is, well, a little fragile. > > I don't think implementing (B) makes the code more fragile than it > already is. That's true. I'll put together a patch for (B) in a few days, then. After I finish the host of changes needed for MIPS GNU/Linux signal backtracing... it's proving quite complicated :) -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer