From owner-freebsd-arch@freebsd.org Fri Nov 13 23:12:42 2015 Return-Path: Delivered-To: freebsd-arch@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id C5ADFA2E8AE for ; Fri, 13 Nov 2015 23:12:42 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 8648B1EA9 for ; Fri, 13 Nov 2015 23:12:42 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from ralph.baldwin.cx (c-73-231-226-104.hsd1.ca.comcast.net [73.231.226.104]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id A5060B989; Fri, 13 Nov 2015 18:12:40 -0500 (EST) From: John Baldwin To: Marius Strobl Cc: freebsd-arch@freebsd.org Subject: Re: Supporting cross-debugging vmcores in libkvm (Testing needed) Date: Fri, 13 Nov 2015 11:50:37 -0800 Message-ID: <5385051.zAN7Yc63R0@ralph.baldwin.cx> User-Agent: KMail/4.14.3 (FreeBSD/10.2-STABLE; KDE/4.14.3; amd64; ; ) In-Reply-To: <20151112234146.GA76156@alchemy.franken.de> References: <3121152.ujdxFEovO3@ralph.baldwin.cx> <111428878.dys4vNKReT@ralph.baldwin.cx> <20151112234146.GA76156@alchemy.franken.de> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Fri, 13 Nov 2015 18:12:40 -0500 (EST) X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 Nov 2015 23:12:42 -0000 On Friday, November 13, 2015 12:41:46 AM Marius Strobl wrote: > On Thu, Nov 12, 2015 at 02:36:42PM -0800, John Baldwin wrote: > > On Monday, August 31, 2015 02:21:19 PM John Baldwin wrote: > > > On Wednesday, August 12, 2015 10:50:20 AM John Baldwin wrote: > > > > On Tuesday, August 04, 2015 10:56:09 AM John Baldwin wrote: > > > > > Many debuggers (recent gdb and lldb) support cross-architecture debugging > > > > > just fine. My current WIP port of kgdb to gdb7 supports cross-debugging for > > > > > remote targets already, but I wanted it to also support cross-debugging for > > > > > vmcores. > > > > > > > > > > The existing libkvm/kgdb code in the tree has some limited support for > > > > > cross-debugging. It requires building a custom libkvm (e.g. libkvm-i386.a) > > > > > and custom kgdb for each target platform. However, gdb (and lldb) both > > > > > support multiple targets in a single binary, so I'd like to have a single > > > > > kgdb binary that can cross-debug anything. > > > > > > > > > > I started hacking on libkvm last weekend and have a prototype that I've used > > > > > (along with some patches to my kgdb port) to debug an amd64 vmcore on an > > > > > i386 machine and vice versa. > > > > > > > > > > ... > > > > > > > > > > What I'm mostly after is comments on the API, etc. Once that is settled I > > > > > will move forward on converting and/or stubbing the other backends (the > > > > > stub route would be to only support other backends on native systems for > > > > > now). > > > > > > > > I guess this is closer to a nuclear power plant than a bikeshed judging by the > > > > feedback. I have ported the rest of the MD backends and verified that the > > > > updated libkvm passes a universe build (including various static assertions > > > > for the duplicated constants in other backends). What I have not done is any > > > > runtime testing and I would like to ask for help with that now. In particular > > > > I need someone to test that kgdb and/or ps works against a native core dump > > > > on all platforms other than amd64 and i386. Note that some of the trickiness > > > > is that the backends now have to make runtime decisions for things that were > > > > previously compile-time decisions. The biggest one affected by this is the > > > > MIPS backend as that backend handles three ABIs (mipso32, mipsn32, and mipsn64). > > > > I believe I have the handling for that correct (mips[on]32 use 32-bit KSEGs > > > > where as mipsn64 uses the extended segments and compat32 KSEGS, and mipso32 > > > > uses 32-bit PTEs and mipsn32/n64 both use 64-bit PTEs) (plus both endians > > > > for both in theory). The ARM backend also handles both endians (in theory). > > > > > > > > Another wrinkle is that sparc64 uses its own dump format instead of writing > > > > out an ELF file. I had to convert the header structures to use fixed-width > > > > types to be cross-friendly. It would be good to ensure that a new libkvm > > > > can read a vmcore from an old kernel and vice versa to make sure my conversion > > > > is correct (I added an explicit padding field that I believe was implicit > > > > before). > > > > > > > > The code is currently available for review in phabric at > > > > https://reviews.freebsd.org/D3341 > > > > > > > > To test, you can run 'arc patch D3341' in a clean tree to apply the patch. > > > > > > I've just rebased this to port aarch64's minidump support. I just need people > > > willing and able to test on non-x86. Testing with the in-tree kgdb using an > > > updated libkvm would be sufficient. > > > > After a lot of crickets, I have updated the manpages for the new API. I will > > commit this "soon". If you want kgdb to keep working on your non-x86 > > platform, this is your chance to test this before it hits the tree. > > > > What exact test procedure do you suggest for full coverage of an > architecture? Just ensuring that kgdb and things like ps -M -N still work. Btw, Mark Linimon tried to generate a crashdump for me on his sparc64 running HEAD recently so I could test the updated kgdb but it failed to generate a dump. I was hoping that the thread on sparc64 with the guy from qemu would result in working qemu as that would let me do the testing I need for this and kgdb locally. -- John Baldwin