[TUHS] pdp11 UNIX memory allocation.
Ronald Natalie
ron at ronnatalie.com
Wed Jan 7 07:57:14 AEST 2015
> 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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