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Re: assembler/bytecode interface

daemon@ATHENA.MIT.EDU (Sat Mar 11 00:30:53 1995 )

Date: Fri, 10 Mar 95 21:27:45 -0800
From: jsp@betz.biostr.washington.edu (Jeff Prothero)
To: coldstuff@MIT.EDU

| > Great idea.  Could the data format for the "assembly code" PLEASE be
| > published?
| I certainly hope not.  The internal byte codes used by the Coldmud
| server are an implementation detail.

What I've done in Muq is to provide an Assembler class
which encapsulates the assembly process and guarantees
that only correct executables get produced, while allowing
full in-db flexibility.  The interface looks approximately

   make-assembler    ( create an instance )
   reset             ( start a new assembly )
   assemble-call     ( assemble a call to a function.
                       If the 'function' is actually a primitive,
                       the appropriate bytecode is deposited
                       instead of an actual CALL.  This keeps the
                       distinction between >most< prims and fns
                       transparent even to in-db compilers, which
                       frees me to move functionality from in-server
                       to in-db in successive releases. )
   assemble-label    ( Deposit a logical target for a branch. )
   assemble-bra      ( Deposit a branch to given label.  May precede
                       label. )
   [...]             ( A few more calls that deposit special stack-
                       hacking instructions for exception handling,
                       and obscure stuff like that. )
   finish-assembly   ( Wraps it all up and returns an executable object.
                       Aborts if there are jumps to missing labels or
                       such.  Makes sure there is a RETURN at the end. )

Thus, there's no "assembly language" in the texual sense (well, for
internal debugging I have a symbolic bytecode assembler, but that's
another issue entirely) but in-db code can assemble arbitrary (rational)

(You can poke around http://betz.biostr.washington.edu/~jsp/muq/muq.html
if you want the gory details.)