Of course PC is the replacement for SVC. You have to look at SVC when PC came
out and how it was being used. It doesn't matter what it was on OS/360. PC came
out when address spaces and running authorized was available. Nearly every
feature of PC was implemented to address use cases of SVC (e.g. xmem,
limitations and restrictions). Even non-authorized came from an SVC use case
(running non-authorized as much as possible).
Can you name any PC instruction features that don't fill a niche we needed in
SVC? Remember that there were a lot of tricks we used to get around SVC's
limitations.
As for "executing authorized code in other address spaces", I actually meant
any address space. I was not thinking specifically about running code located
in private which was another problem we had with SVC.
Jon.
On Thursday, August 29, 2019, 09:49:03 AM PDT, Tom Marchant
<[email protected]> wrote:
On Thu, 29 Aug 2019 04:22:02 +0000, Jon Perryman wrote:
>The PC instruction is a replacement for SVC. Both instructions exist
>solely to run authorized programs in other address spaces.
No. The SVC instruction, as implemented by OS/360 and its descendants,
exists to provide a service that requires execution in Supervisor state.
The concepts of address spaces and authorized programs didn't exist
until years later.
While a common use case for PC routines is to execute code in another
address space, that is not its only use case. Also, PC routines can be
defined which receive control in problem state.
--
Tom Marchant
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