From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 18140 invoked by alias); 3 Jan 2007 11:37:22 -0000 Received: (qmail 18131 invoked by uid 22791); 3 Jan 2007 11:37:22 -0000 X-Spam-Check-By: sourceware.org Received: from sibelius.xs4all.nl (HELO brahms.sibelius.xs4all.nl) (82.92.89.47) by sourceware.org (qpsmtpd/0.31) with ESMTP; Wed, 03 Jan 2007 11:37:15 +0000 Received: from brahms.sibelius.xs4all.nl (kettenis@localhost.sibelius.xs4all.nl [127.0.0.1]) by brahms.sibelius.xs4all.nl (8.13.8/8.13.8) with ESMTP id l03Bb2YF026882; Wed, 3 Jan 2007 12:37:02 +0100 (CET) Received: (from kettenis@localhost) by brahms.sibelius.xs4all.nl (8.13.8/8.13.8/Submit) id l03Bb0rT031898; Wed, 3 Jan 2007 12:37:00 +0100 (CET) Date: Wed, 03 Jan 2007 11:37:00 -0000 Message-Id: <200701031137.l03Bb0rT031898@brahms.sibelius.xs4all.nl> From: Mark Kettenis To: drow@false.org CC: gdb-patches@sourceware.org In-reply-to: <20070101200248.GA19073@nevyn.them.org> (message from Daniel Jacobowitz on Mon, 1 Jan 2007 15:02:48 -0500) Subject: Re: [patch RFC] Re: Notes on a frame_unwind_address_in_block problem References: <20060706222157.GA1377@nevyn.them.org> <200607132020.k6DKKCSB023812@elgar.sibelius.xs4all.nl> <20060718183910.GB17864@nevyn.them.org> <20070101191927.GA14930@nevyn.them.org> <200701011954.l01Js85r031019@brahms.sibelius.xs4all.nl> <20070101200248.GA19073@nevyn.them.org> Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2007-01/txt/msg00061.txt.bz2 > Date: Mon, 1 Jan 2007 15:02:48 -0500 > From: Daniel Jacobowitz > > On Mon, Jan 01, 2007 at 08:54:08PM +0100, Mark Kettenis wrote: > > Well, I really can't say I like it. The problem is that it's been > > several months since we last discussed this problem, so I'll have to > > start to think again from scratch :(. Isn't it just a matter of > > Yeah, sorry about that. Anyway, I'm happy to discuss alternatives; > I don't like it much either. I have thought about this for a bit now, and I think I have found a way out. But let me first start by being a bit more specific about why I think your change is so bad: The basic principle of unwinding is that you get information about THIS_FRAME from NEXT_FRAME; you always walk the frame chain in one direction. This means that the only requirement for calling frame_unwind_xxx functions is that you have a NEXT_FRAME. Your change introduces a function that breaks this rule, by requiring THIS_FRAME to be there, walking the frame chain in the other direction. And it didn't take you very long to hit the problem with that: infinite recursion. Now the problem we're facing is that frame_unwind_address_in_block() (frame_func_unwind() is nothing but a fancy wrapper around that call) cannot be implemented reliably without knowledge about THIS_FRAME; it needs to know whether THIS_FRAME could be a fake frame set up by the kernel in order to determine whether it is a good idea to adjust the unwound PC or not. In our current implementation that information is carried by the frame type. The solution I think, is to pass this information explicitly to frame_unwind_address_in_block(), i.e. we change it's prototype from: CORE_ADDR frame_unwind_address_in_block (struct frame_info *next_frame); into CORE_ADDR frame_unwind_address_in_block (struct frame_info *next_frame, enum frame_type *this_type); Of course get_frame_address_in_block() doesn't need this extra argument, and would be implemented as: CORE_ADDR get_frame_address_in_block (struct frame_info *this_frame) { return frame_unwind_address_in_block (this_frame->next, get_frame_type (this_frame)); } If you think a bit further (almost) all cases where we currently call frame_unwind_address_in_block() in sniffers, we really need to specify THIS_FRAME's type explicitly. So signal frame sniffers would need to do call frame_unwind_address_in_block (next_frame, SIGTRAMP_FRAME). Doing so in the dwarf2_signal_frame_this_id() would fix the bug we're trying to fix. Mark