[COFF] machine code translation,as mental architecture models

[Aron Insinga]

On 7/13/24 19:46, John Levine wrote:
> It appears that Douglas McIlroy <douglas.mcilroy at dartmouth.edu> said:
>> -=-=-=-=-=-
>>
>>> the DEC PDP-1 MACRO assembler manual says that a macro call
>>> is expanded by copying the *sequence of 'storage words' and
>>> advancing the current location (.) for each word copied*
>>> I am quite surprised.
> I looked at the manual and I think he's misreading it. The "words" in
> question are the tokens in the macro definition.
>
> The example macros look pretty straightforward, instructions and
> pseudo-ops that are expanded replacing dummy arguments by actual ones.
> There's no conditional assembly so each macro is just a parameterized
> chunk of code.
>
> https://bitsavers.org/pdf/dec/pdp1/PDP-1_Macro.pdf
>
> R's,
> John

Possibly, but they use 'syllables' for tokens (symbols or integers), and 
they say here that they advance the location counter after each word 
copied.  If they were copying characters into the input stream, they 
would not be incrementing the location counter ('.') after each word 
transferred.

And as you say, it is simple parameter substitution, so tracking which 
macro argument goes into which instruction's address field is easy.  The 
instruction format is simple.  So for each line in the macro definition 
body, if the opcode is a memory reference instruction, put the argument 
number in the binary instruction address field before storing the 
instruction word in a list/block. When expanding the macro, if the 
opcode is a memory reference instruction, get the argument number from 
the address field and replace it with the symbol table value of the 
symbol passed in as the actual argument, and store the word in the 
output stream (and incrememnt '.').

I haven't yet gotten the 18-bit-but-incompatible PDP-4 documentation for 
comparison.  [IIRC the PDP-4 assembler was the one with a single pass 
assembler that punched the symbol table at the end of the tape, and the 
clever loader that read the tape upside down and backwards to first 
rebuild the symbol table and then fix up the instructions and load them 
into memory.]

- Aron