From mboxrd@z Thu Jan 1 00:00:00 1970 From: random832@fastmail.us (random832@fastmail.us) Date: Tue, 06 Jan 2015 15:33:53 -0500 Subject: [TUHS] pdp11 UNIX memory allocation. In-Reply-To: <54AC4394.3050302@update.uu.se> References: <54AC4394.3050302@update.uu.se> Message-ID: <1420576433.410248.210385277.513EF8EC@webmail.messagingengine.com> On Tue, Jan 6, 2015, at 15:20, Johnny Billquist wrote: > Later model PDP-11 processors had a hardware feature called split I/D > space. This meant that you could have one 64Kb virtual memory space for > instructions, and one 64Kb virtual memory space for data. Was it possible to read/write to the instruction space, or execute the data space? From what I've seen, the calling convention for PDP-11 Unix system calls read their arguments from directly after the trap instruction (which would mean that the C wrappers for the system calls would have to write their arguments there, even if assembly programs could have them hardcoded.)