[Info-vax] Virtual memory 101 (was Re: Android development...)

[JF Mezei]

On 14-09-23 16:02, Stephen Hoffman wrote:

> <http://h71000.www7.hp.com/doc/73final/5841/5841pro_078.html#user_written_sys> 
> documentation.

is this the key ?

"In addition, because user-written system services are called using the
system service dispatcher,"

So basically, when I call a system service, I don't branch to that code,
I branch to a stub which calls $CMKRNL with the real SYS$QIO entry point
as argument. Right ?

But that doesn't answer my question it only moves it to a stub routine:

When my user mode program executes a call/branch instruction to the
address that SYS$QIO has been resolved to, how come the next
instructions that are executed magically gain the ability to perform
whatever SYS$CMKRNL does ?

Does the mode automatically get activated when the code being executed
is inside special range of memory pages that have some bit set to
automatically enable that capability ?