Re: iseries pgm call support

["Bob Donovan" <rjd@xxxxxxxxxx>]

On 07/12/2001 at 11:59:43 AM, steve richter wrote:

     Here is my list of iseries architecture features that  Rochester is
failing to exploit:

1. External module call. Single level store enables a running  pgm to jump
to code in an external object/module. This jump can execute as  quickly as
jumping to code within the pgm itself. Would enable true  modularization of
the code of an application.

Not provided so as not to detract from the ile model  monster.  ile must
exist so the iseries can mimic lesser platforms that the  iseries is
striving to be compatible with.

Steve,

The devil is in the details.  As I understand your proposal, I see a number
of technical details that must be addressed to make this feature usable and
robust.  Here are some things that come to mind:

o The proposal must address register usage.  What rules will you define for
register usage across the transfer of control?  If the external module
needs to use registers n through m, will the called module save and restore
them?  If so, where (such that the code is reentrant)?  Will these
conventions coexist with other programs on the system?  For example, can I
call off to existing runtime library functions?

o Will you allow passing parameters to the external modules?  How?

o What mechanism will you use for returning to your caller?

o How do the caller's obtain the address of the external module?   What if
I need to change the external module ... will all of the caller's be
updated with the new address (even if they are currently running)?

o Can external modules define data?  If so, explain how you might support
static or automatic variables.

As you address these details, I think you might come up with something that
is pretty similar to the existing mechanisms for transferring control
between code e.g., dynamic program calls and static binding).  If not, then
I would agree that Roch needs to take a closer look.

- Bob Donovan  rjd@us.ibm.com



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