Re: What's all this about Swarm modifying the runtime?

[Scott Christley]

On Monday, September 30, 2002, at 05:59 AM, Paul Johnson wrote:

> I don't even really know what "runtime" means, so take this with a 
> grain of salt.

When I speak about the "runtime", I am generally speaking about all of 
the bits that are provided by GCC, the GNU compiler.  This includes the 
code which parses/compiles ObjC  code as well as the libobjc.a library.  
A more strict definition of "runtime" is just the libobjc.a library; 
meaning the functions used by ObjC programs when they are being "run."


> Does Swarm really use a different runtime?

The basic answer is Yes, but the details are less clear.  In this case, 
Swarm has its own version of the libobjc.a library.  You can see this in 
the Swarm source code by the libobjc directory which correlates to the 
libobjc directory in the GCC source code.

From reading the ChangeLog, it appears that Marcus added mframe support 
from GNUstep, automake/libtool for building libobjc.a, changes to some 
runtime functions to use mframe support, and various bug fixes.  mframe 
is processor specific code for dynamically constructing/deconstructing 
stack frames for function calls; GNUstep uses it for its distributed 
objects.

I'm unsure how Swarm is using the mframe code though; it is referenced a 
few places with the defobj code.  It may just be used for the 
integration of Java and ObjC, or it may be central to ObjC method calls 
within Swarm.  My guess is the former because you only really need 
mframe support for proxies and forwarding.

So Paul, when you say that you are able to compile Swarm with the newer 
GCC; it may be that the libobjc directory within Swarm is being compiled 
and being used instead of the libobjc.a supplied by GCC.  I would guess 
this has to be the case because when you compile heatbugs, it would 
complain about not being able to find the mframe functions if GCC's 
libobjc.a was used.

cheers
Scott


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