[TUHS] pdp11 UNIX memory allocation.

[clemc@ccc.com (Clem Cole)]

Right - that's how the kernel set up the page tables for the user processes.

On Tue, Jan 6, 2015 at 4:57 PM, Ronald Natalie <ron at ronnatalie.com> wrote:

>
> > On Jan 6, 2015, at 3:33 PM, random832 at fastmail.us wrote:
> >
> > Was it possible to read/write to the instruction space, or execute the
> > data space?
>
> In split I/D mode (411) magic number.    It is imposible to execute in D
> space or use regular data access instructions to access i-space.   The
> addresses are in completely different spaces (i.e, 0 in data is mapped to
> different memory than 0 in instruction space).  Some access at the kernel
> level can be done with MFPI and MPFD instructions.
>
> In write protected, non-split more (410 magic), you could read the I space
> and you could jump in to D space.   You were prohibited to write the i
> space.
>
> In non protected mode (407 magic) everything was fair game.
>
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