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

[Mark Morgan Lloyd]

Bernd Oppolzer wrote:
> Am 21.08.2013 22:17, schrieb Steve:
>> Mark Morgan Lloyd wrote
>>
>>> > Otherwise we also rely on external tools (mostly the GNU linker)
>>> > here. So as a first step you'd choose the approach of using an
>>> > external assembler and linker, because simply calling a third party
>>> > utility is easier than completely implementing an internal assembler
>>> > and linker.
>>>
>>> With the caveat here that as I understand it experienced IBM programmers
>>> avoid the GNU assembler like the plague, since it doesn't have anything
>>> like the sort of macro facilities they're used to. By implication, that
>>> would imply that they prefer to avoid the GNU linker and related tools
>>> as well.
>>
>> There is a problem inherent in this discussion; zArch is not one 
>> environment!
>> It's one architecture supporting multiple operating systems, much like 
>> the
>> 386/486/586/686 etc supports Linux or DOS or OS/2 or Windows (all 37 
>> versions)
>> etc. zArch has MVS (in all it's varieties) VM, DOS, LINUX, MFT, MVT, 
>> MUSIC/SP,
>> and loads of other more niche stuff. In addition to all this, later 
>> versions of
>> MVS supply a POSIX compliant shell called OMVS. GNU anything is 
>> available in
>> hardly any of these environments even if we can handle the brain-dead 
>> assembler.
> 
> This is correct, but it should be possible to cover most of those 
> systems with
> one RTL - much the same way as LE (language environment) does it in the
> "big" IBM world, too.

I suspect that targeting "classic" OSes which use EBCDIC would need a 
branch of the RTL, even if the sourcecode in that branch were in ASCII. 
I also suspect that- however attractive this is- trying to port the 
compiler so that it would self-host on EBCDIC-based OSes would 
effectively fork the project, unless somebody could come up with a neat 
hack to automatically convert patches back to ASCII when they're sent to 
the Subversion repository.

Thought for everybody even remotely interested: if we could standardise 
on the first line of every unit being a non-essential comment (and 
specifically, not a compiler directive) then it would be possible for 
the parser to decide whether it were looking at ASCII or EBCDIC before 
hitting anything important.

> compilers. I recently learned a bit about the MIPS architecture, and it 
> seemed to
> me to have some similarities to IBM's, so I guess, a kind of 
> "translation" from MIPS
> to IBM could be successful.

A postcompilation translation probably wouldn't work since e.g. there 
are different ranges of parameters used for compiler passing, but I was 
wondering whether the MIPS directory could be moved en masse. But again, 
note Florian's warning about this.

> to IBM could be successful. Many people say that the IBM platform is the 
> only
> remaining platform today that reasonably can be programmed using 
> assembly language,
> because of the clear structure of the instruction set.

In fairness, the x86 probably falls into that category as well. However 
I think most people abandoned x86 assembler when both Linux and the NT 
family of OSes demonstrated that C was adequate for portable device 
drivers etc.

> I would strongly suggest not to use the "new" hardware stack, but 
> instead to
> rely on the OS linkage conventions (save area chaining, register 13), which
> in fact are used by most of the operating systems mentioned above - with
> minor differences.

Noted, but I think we have to go along with Linux practice for the 
initial port.

-- 
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]