[Info-vax] Reimplementing VMS, was: Re: HP adds OpenVMS Mature Product Support beyond the end of Standard Support

[Johnny Billquist]

On 2014-02-04 10:28, JF Mezei wrote:
> On 14-02-04 08:08, John Reagan wrote:
>
>> The frontends didn't need many changes from Alpha to Itanium as they pretty much figured it out from VAX to Alpha.  Some frontends, like Pascal, have common sources for all three architectures (VAX, Alpha, Itanium).  Others like BASIC, C and COBOL have VAX vs Alpha/Itanium.  Fortran has several due to the F77/F90 transition along the way.
>
>
> Since there are already compilers for x86-64, wouldn't it be simpler to
> just adapt an existing one to support VMS ? Or does the need for Bliss
> and Macro-32 require a x86-64 version of GEM, and once you have that,
> you might as well use the existing compilers that run on VMS ?

There is no existing MACRO-32 for x86-64. Nor is there for any other 
language in the dialects that VMS have, so if you want to use a backend 
that works on x86-64, you instead need to write all the front ends for 
the different languages, and that is most likely a much larger work than 
getting GEM generate x86-64 code.

So there is no explicit requirements for GEM, but there is explicit 
requirements for understanding the specific dialects of the different 
languages as they exist under VMS. What way it gets from source code it 
executable is not important.

> In the case of a C compiler available for both Windows and Linux on x86,
> are the object files that are outputted identical and the linker is the
> one that makes the OS specific executables, or would the object files be
> fo different format ?

Object files might be similar, and might not. Executables might be 
different, and might not. It depends on what formats the kernel can 
understand, and what formats the linker can deal with. But of course, 
the end executable also refers to shared libraries as well as linked in 
libraries that will differ between systems, so the same binary will not 
work under the different OSes anyway.

But the generic format of object files and executables can very well be 
compatible.

	Johnny