[Vm-dev] debugging the garbage collector

[Eliot Miranda]

Hi Noah,

On Fri, Feb 15, 2013 at 5:52 AM, Noah Evans <noah.evans at gmail.com> wrote:
>
> I've taken bert's advice and gotten the canonical svn tree. For the
> moment I've gone away from VMMaker sources and started with the svn
> tree's cointerp.c.

I hope you're not considering editing cointerp.c?  That route is
doomed to failure.  You need to start from the VMMaker and Slang
source and generate legal C.  Does cointerp.c compile?  If not, what
errors are you getting?  What's preventing compilation?

> Once I have that working (most of it already
> compiles, I just need to decide what to do with alloca--it's
> unimplemented in Plan9 posix emulation).

Hmm.  If Plan9 supports anything like a POSIX threads system then you
may have to implement alloca.  The issue here is that Cog runs machine
code in the stack zone which is usually allocated using alloca, and
that alloca allocates memory on the C stack, so allocating the stack
zone via alloca arranges that the stack zone is also on the C stack.
Some (e.g. older linux) thread implementations derive the thread id
from the stack pointer.  On these implementations it is essential to
allocate the stack zone via alloca so that thread determination is
correct within machine code.  Luckily this thread id being encoded in
the stack pointer (because each thread gets its own distinct stack) is
giving way to a more modern one using a segment register to implement
the pointer to the thread control block.  So if you can't implement
alloca and/or the thread system doesn't depend on the stack pointer
for thread id, you can simply use malloc, e.g.
#define alloca(n) malloc


> I'll go back and work with
> Spoon. I'm just trying to minimize the number of variables for the
> moment. The svn tree has been really great in this regard.

>
> Can anyone point me to a contributing page for how to submit patches?
> Or just to the mailing list proper?

You can send patches to me.  I maintain (and authored) the Cog branch.

>
> Noah
>
>
> On Fri, Feb 15, 2013 at 2:47 PM, David T. Lewis <lewis at mail.msen.com> wrote:
>>
>> On Fri, Feb 15, 2013 at 01:14:17PM +0100, Bert Freudenberg wrote:
>>>
>>> On 2013-02-15, at 11:27, Noah Evans <noah.evans at gmail.com> wrote:
>>>
>>> > Craig, which version of Cog are you using? I'm using the tip of the
>>> > gitorious tree.
>>>
>>> Eliot's canonical sources are in subversion:
>>>
>>> http://squeakvm.org/svn/squeak/branches/Cog/
>>>
>>
>> Oh dear, I suspect we may have some confusion here. Craig says:
>>
>>
>>>      The current release of Spoon is 3 beta 3 (23 October 2012),
>>> available at:
>>>
>>>      http://netjam.org/spoon/releases/current
>>>
>>>      It includes a Squeak 4.2 object memory (4 February 2011) with
>>> VMMaker dtl.237 (23 May 2011) installed, and the Spoon VM changes
>>> applied to that, and with remote browsing support installed. It runs on
>>> the VM it generates, which is the only one supplied in the release (Mac
>>> OS, Linux and win32).
>>
>> Noah, what platform sources did you start with? The VM that Craig
>> describes would have been compiled with platform sources from the
>> trunk VM (not branches/Cog). Those sources are at:
>>
>>   http://squeakvm.org/svn/squeak/trunk
>>
>> You would need to use a version of those sources from the early 2011
>> time frame. But I would suggest very stongly that you get an exact
>> copy of sources from Craig so that you are starting from exactly the
>> same code base that he is using (or maybe that's what you meant in your
>> question to Craig the about gitorious tree).
>>
>> Mixing generated source code from VMMaker trunk (e.g. VMMaker-dtl.237)
>> with platform sources from branches/Cog will definitely not work.
>> And mixing generated sources (from VMMaker) with platform sources
>> (from Subversion) that are not from the same general time frame will
>> probably not work.
>>
>> Dave
>>



-- 
best,
Eliot