[Gc] Porting gc to IBM AS/400

Ben Hutchings ben.hutchings at businesswebsoftware.com
Thu Oct 14 02:17:01 PDT 2004

Peter Colson wrote:
> On 14/10/2004, at 3:17 AM, Ben Hutchings wrote:
>> Peter Colson wrote:
>>   (If it is purely stack-based then there may be no need to write any 
>> machine-specific code.)
> Indeed, maybe that's what I'm looking at here. If that's the case libgc 
> only needs to be able to scan statically allocated memory or stack 
> allocated memory. The pushing of registers onto the stack can be ignored 
> (GC_generic_push_regs, that is). How does this sound?

It sounds reasonable.  Of course you still need to locate the stack(s) 
but one of the sort-of-portable heuristics may work.

>>   I believe there is an assembly language for this virtual machine.
> If there is it's well hidden! I'm told the compiler actually produces 
> instructions in intermediate code form that pass through a Common Use 
> Back End (CUBE) that can then access machine capabilities. There is 
> further processing and a System Licensed Internal Code (SLIC) layer 
> (hiding the underlying hardware?). Also, the compiler (or the code 
> produced by it) has a certain privileged access level not available to 
> application programs.
> Common users only get to see the abstract MI layer which has no concept 
> of registers.

The MI compiler is approximately an assembler, though.  Apparently there 
is also a lower-level assembly language called W-code which is used by 
the more modern AS/400 compilers but is not publicly documented.


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