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: >=20 > > On Jul 20, 2016, at 2:19 PM, John Baldwin <jhb@freebsd.org> wrote: > >=20 > > On Wednesday, July 20, 2016 01:20:34 PM Sean Bruno wrote: > >>=20 > >> 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 prima= ry objection > >>>> (certainly my main one) was that the in-tree kgdb was the only k= ernel debugger > >>>> available. kgdb is now available via the devel/gdb port in port= s (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). > >>>>=20 > >>>> There are some issues still with devel/gdb: namely it does not c= urrently > >>>> 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. > >>>>=20 > >>>> 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 sh= ould default > >>>> to enabling lldb and disabling gdb for platforms that meet the f= ollowing > >>>> criteria: > >>>>=20 > >>>> 1) devel/gdb works including thread and kgdb support > >>>> 2) lldb works > >>>>=20 > >>>> We could perhaps be more aggressive and handle lldb and gdb togg= les > >>>> 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 mi= ght be if > >>>> we end up with platforms where 1) is true but 2) is not (such as= powerpc). > >>>>=20 > >>>> I believe that these conditions are only true for x86 currently.= > >>>>=20 > >>>> Comments? > >>>=20 > >>> I believe I've fixed the one last thing that was depending on /us= r/bin/gdb > >>> (crashinfo) to use devel/gdb if it is present. I'd either like t= o 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 b= ase is > >>> equally dysfunctional). > >>>=20 > >>> However, to start with: > >>>=20 > >>> 1) Does anyone have a reason to keep /usr/bin/gdb on amd64? > >>>=20 > >>> 2) Does anyone have a reason to keep /usr/bin/gdb on !amd64? > >>>=20 > >>=20 > >> I don't have an immediate use case in the mips/mips64 case. Shoul= d > >> ports "just work" here or do I need some kind of "cross gdb"? > >=20 > > 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 Fr= eeBSD/mips > > at all. Does /usr/bin/gdb work on mips? >=20 > It does, kinda. there=E2=80=99s a lot of stuff it gets right, so it c= an be useful. However, > there=E2=80=99s enough wrong that it=E2=80=99s super frustrating. So = there=E2=80=99s 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=E2=80=99m all for re= placement. >=20 > If /usr/bin/gdb were super duper cool on mips, I=E2=80=99d have a dif= ferent 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/gd= b on all platforms you'd be left with no debugger at all. Starting with amd64 i= s probably the most prudent for now. i386 is probably also a good candidate even = without working lldb. --=20 John Baldwin
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