[TUHS] mental architecture models, Anyone ever heard of teaching a case study of Initial Unix?

[Aron Insinga]

See https://www.cs.tufts.edu/~nr/cs257/archive/ronald-brender/bliss.pdf

C allowed writing Unix with a limited amount of assembly code, but CMU's 
original BLISS-10 was designed to write an operating system with *no* 
outside assembly code.  Features like the 'MACHOP' (machine operation) 
builtin function made use of  the orthogonality of the PDP-10 
instruction format to execute machine-specific instructions in-line.  
(cf. the 'asm' extensions in some implementations of C.)  The PDP-10's 
36-bit word allowed single-precision floating point numbers to fit in 
machine words, so it had infix operators for both integer and 
single-precision floating point operations (which I presume were 
adequate for an operating system).

When DEC chose an implementation language, they knew about C but it had 
not yet escaped from Bell Labs.  PL/I was considered, but there were 
questions of whether or not it would be suitable for a minicomputer.  On 
the other hand, by choosing BLISS, DEC could start with the BLISS-11 
cross compiler running on the PDP-10, which is described in
https://en.wikipedia.org/wiki/The_Design_of_an_Optimizing_Compiler
BLISS-11 and DEC's Common BLISS had changes necessitated by different 
word lengths and architectures, including different routine linkages 
such as INTERRUPT, access to machine-specific operations such as INSQTI, 
and multiple-precision floating point operations using builtin functions 
which used the addresses of data instead of the values.

In order to port VMS to new architectures, DEC/HP/VSI retargeted and 
ported the BLISS compilers to new architectures.

What I find amazing is that they also turned the VAX MACRO assembly 
language (in which some of the VMS operating system was written) into a 
portable implementation language by 'compiling' the high-level CISC VAX 
instructions (and addressing modes) into sequences of RISC 
instructions.  I believe that this is similar to how modern CPU chips 
dynamically translate x86_64 instructions (or whatever) to an internal 
RISC format.

- Aron

(Disclaimer: I worked at DEC for a long time and VSI for a short time, 
but I wasn't responsible for the above work.)


On 7/6/24 17:32, Charles H Sauer (he/him) wrote:
> On 7/6/2024 3:56 PM, John R Levine wrote:
>> On Sat, 6 Jul 2024, Clem Cole wrote:
>>> Other systems programming languages followed, BCPL, BLISS, PL/360 
>>> and even
>>> B before C.
>> The original version of BLISS was only for the PDP-10.  DEC 
>> retargeted it to the PDP-11 and VAX, but I think that was after Unix 
>> moved to the Interdata and possibly other machines.