[fpc-devel] Re. z370 Cross Compilation, Pass 2 of ....

[Sven Barth]

On 01.09.2013 15:49, Bernd Oppolzer wrote:

Most points were already answered by Jonas, so I'll only tackle the 
remaining ones:

> BTW: is it possible to print the linear assembler representation - the
> outcome of step 2 -
> which in my understanding is NOT target-specific - and compare it - for
> example - to
> the assembler code generated for MIPS? I believe that from that mapping
> there could
> indeed be learned something ...

There is currently no way to write this linear assembler representation 
as is. Only through the assembler writers they can be written.

The entries of that linear presentation are mostly located inside the 
aasmtai.pas and $CPUTARGET/aasmcpu.pas units (each tai is one entry 
inside the linear list) with one of the more important ones being taicpu 
as this is the one which encapsulates the platform specific CPU 
instructions.

>>
>> For a new port it is advisable to not implement internal assemblers
>> and linkers, because that means more work, but to use existing tools
>> for the given platform. And here like for the RTL assembler/linker
>> interfaces for the GNU assembler and linker already exist which
>> simplify a port. Later on additional assembler/linker interfaces for
>> other assemblers/linkers can be added or even an internal assembler
>> and/or linker can be written.
>
> I, too, would try to rely on existing assemblers and linkers,
> but I have the feeling that HLASM (or free Assemblers supporting
> the z-Arch vocabulary) is a better choice than gas. I believe that
> there are some people out there waiting for FPC being available
> on z-Arch, and they are not all Unix-aware, but they read and
> understand the classical z-machinery well and would like it,
> if FPC was available there, without additional prerequisites
> (from their point of view).

The point is still that one should choose Linux as a first target OS for 
that new platform and thus the assembler must be supported there as 
well. As GNU as is normally always there where there is a Linux this 
would mean that for the first steps of the implementation no new 
assembler writer needs to be implemented (though this isn't necessarily 
rocket science). If HLASM supports assembling code for Linux you can of 
course implement that as first.
My suggestion is however to only implement as few things as possible as 
the first step which means "only" implementing the code generator and no 
new RTL, no assembler writer and no linker interface. Later on once 
Linux works good enough (not everything needs to be implemented for 
this!) additional assembler writers or target OSes can be added. You are 
working inside an unfamiliar environment (the compiler's code) and thus 
you should it make yourself as easy as possible. Otherwise you might 
experience frustration when doing this port...

Regards,
Sven