Date: Wed, 20 Jul 2016 14:39:55 -0600 From: Warner Losh <wlosh@bsdimp.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-arch@freebsd.org, Sean Bruno <sbruno@freebsd.org> Subject: Re: Retiring in-tree GDB Message-ID: <B11C1EC4-B7D4-43DA-A291-5DDF0D1AC2B8@bsdimp.com> In-Reply-To: <3871457.xzmrTRH8AM@ralph.baldwin.cx> References: <2678091.es0AGJQ0Ou@ralph.baldwin.cx> <4450836.nX37FfBzNy@ralph.baldwin.cx> <068a0167-1d5d-a437-60e7-b74e407060a2@freebsd.org> <3871457.xzmrTRH8AM@ralph.baldwin.cx>
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> 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 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). >>>>=20 >>>> 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. >>>>=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 = should default >>>> to enabling lldb and disabling gdb for platforms that meet the = following >>>> 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 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). >>>>=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 = /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). >>>=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. Should >> 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 = FreeBSD/mips > at all. Does /usr/bin/gdb work on mips? It does, kinda. there=E2=80=99s a lot of stuff it gets right, so it can = 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 = replacement. If /usr/bin/gdb were super duper cool on mips, I=E2=80=99d have a = different take, but gdb on mips has never been stellar. Warner=
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