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From: quadibloc <quadibloc@gmail.com>
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Subject: Re: Why I've Dropped In
Date: Sun, 15 Jun 2025 19:29:23 +0000
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On Sat, 14 Jun 2025 16:45:23 +0000, Stephen Fuld wrote:
> On 6/14/2025 3:48 AM, Thomas Koenig wrote:

>> Which made nonsense the concept of making data relocatable by
>> always using base registers.
>
> Forgive me, but I don't see why.  When the program is linked, the COMMON
> block is at some fixed displacement from the start of the program.  So
> the program can "compute" the real address of the data in common blocks
> from the address in its base register.

The purpose of a COMMON block is to share variables between the main
program and subroutines.

On the System/360, a FORTRAN compiler typically compiled each subroutine
in a program separately from every other subroutine. They just got
linked together by the linking loader in order to run.

So no subroutine would know where a COMMON block created by loader for
the main program would be unless that information was given to it - and
the loader would give it that information, in the form of a full 24-bit
address constant, so it didn't have to be passed as a parameter.

John Savard