Retiring in-tree GDB

[Warner Losh]

> On Jul 20, 2016, at 2:19 PM, John Baldwin <jhb at 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.

Warner