Date: Wed, 20 Jul 2016 14:30:01 -0700 From: John Baldwin <jhb@freebsd.org> To: Warner Losh <wlosh@bsdimp.com> Cc: freebsd-arch@freebsd.org, Sean Bruno <sbruno@freebsd.org> Subject: Re: Retiring in-tree GDB Message-ID: <2386413.0UUCRd2KC2@ralph.baldwin.cx> In-Reply-To: <B11C1EC4-B7D4-43DA-A291-5DDF0D1AC2B8@bsdimp.com> References: <2678091.es0AGJQ0Ou@ralph.baldwin.cx> <3871457.xzmrTRH8AM@ralph.baldwin.cx> <B11C1EC4-B7D4-43DA-A291-5DDF0D1AC2B8@bsdimp.com>
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On Wednesday, July 20, 2016 02:39:55 PM Warner Losh wrote: > > > On Jul 20, 2016, at 2:19 PM, John Baldwin <jhb@freebsd.org> wrote: > > > > On Wednesday, July 20, 2016 01:20:34 PM Sean Bruno wrote: > >> > >> On 07/20/16 13:00, John Baldwin wrote: > >>> On Tuesday, October 20, 2015 01:36:28 PM John Baldwin wrote: > >>>> When this topic was last raised (by Warner I believe), the primary objection > >>>> (certainly my main one) was that the in-tree kgdb was the only kernel debugger > >>>> available. kgdb is now available via the devel/gdb port in ports (and as of > >>>> last week was enabled by default, so 'pkg install gdb' will get you a kgdb > >>>> binary). The kgdb in ports is in general superior to the one in the base > >>>> system. It is a cross debugger by default (and with my pending patches to > >>>> libkvm it even supports cross debugging of vmcores). > >>>> > >>>> There are some issues still with devel/gdb: namely it does not currently > >>>> support some of the platforms supported by our in tree gdb such as arm and > >>>> mips. For these platforms I think the in-tree gdb will need to remain until > >>>> there is a suitable alternative. > >>>> > >>>> However, I would like to propose that we retire the in-tree GDB for some of > >>>> our platforms (namely x86) for 11. In particular, I think we should default > >>>> to enabling lldb and disabling gdb for platforms that meet the following > >>>> criteria: > >>>> > >>>> 1) devel/gdb works including thread and kgdb support > >>>> 2) lldb works > >>>> > >>>> We could perhaps be more aggressive and handle lldb and gdb toggles > >>>> independently, but I think we want to ship some sort of userland debugger > >>>> out of the box on all of our platforms. The question I think might be if > >>>> we end up with platforms where 1) is true but 2) is not (such as powerpc). > >>>> > >>>> I believe that these conditions are only true for x86 currently. > >>>> > >>>> Comments? > >>> > >>> I believe I've fixed the one last thing that was depending on /usr/bin/gdb > >>> (crashinfo) to use devel/gdb if it is present. I'd either like to disable > >>> the base gdb on amd64 in the next week or so on HEAD, or perhaps if people are > >>> really gutsy, disable it for all platforms on HEAD. We still don't have kgdb > >>> in ports for non-x86 (though for ppc at least kgdb in ports and base is > >>> equally dysfunctional). > >>> > >>> However, to start with: > >>> > >>> 1) Does anyone have a reason to keep /usr/bin/gdb on amd64? > >>> > >>> 2) Does anyone have a reason to keep /usr/bin/gdb on !amd64? > >>> > >> > >> I don't have an immediate use case in the mips/mips64 case. Should > >> ports "just work" here or do I need some kind of "cross gdb"? > > > > ports gdb does not yet work on mips. Once it supports mips it will work as > > both a native and cross debugger, but it just doesn't know about FreeBSD/mips > > at all. Does /usr/bin/gdb work on mips? > > It does, kinda. there’s a lot of stuff it gets right, so it can be useful. However, > there’s enough wrong that it’s super frustrating. So there’s a low bar to > replacement. If I can build a new /bin/cat and debug it with a ports gdb, > even if things are broken that kinda work now, I’m all for replacement. > > If /usr/bin/gdb were super duper cool on mips, I’d have a different take, but > gdb on mips has never been stellar. Well, devel/gdb won't work at all on mips, so if we removed /usr/bin/gdb on all platforms you'd be left with no debugger at all. Starting with amd64 is probably the most prudent for now. i386 is probably also a good candidate even without working lldb. -- John Baldwin
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