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From: ifarqhar@sunb.mqcc.mq.oz.au (Ian Farquhar)
Newsgroups: comp.sys.amiga.emulations
Subject: Re: Emulator Mechanics [Transpiler]
Message-ID: <1338@macuni.mqcc.mq.oz>
Date: 13 Mar 91 03:24:04 GMT
References: <5097@mindlink.UUCP>
Sender: root@macuni.mqcc.mq.oz
Organization: Macquarie University, Sydney, Australia.
Lines: 32

In article <5097@mindlink.UUCP> Chris_Johnsen@mindlink.UUCP (Chris Johnsen) writes:
>Ian Farquhar (ifarqhar@sunb.mqcc.mq.oz.au) suggested that a compiled module  be
>run concurrent with an emulator type section so that in some parallel  way, any
>references within the source executable, which would also be loaded during
>runtime of the emulation, could be validated.  It could be argued that this
>should be placed on the pro side of the ledger, but the incurred overhead
>during execution would be large.  This function, I had imagined initially,
>would be carried out during the transpiler phase and not attached to, or
>burdening, the runtime execution.

No, I suggested that an image of the original code, without translation,
be carried around with the compiled code, with indexes into the compiled
code's equivalent sections that would allow jump tables and so forth to
function correctly.  This would be a memory intensive but low-time-overhead
time way of resolving problems.  It should also be noted that such a
system would allow trapping of addresses that need to be handled by
special code (hardware locations etc.), and that the image is also used
for data storage, meaning that once loaded and allocated, the program
would be unlikely to need any further allocation of heap.

This system solves two problems: the data/code differentiation (if you
accidentally compile some data, it is no great problem) though a much
more minor problem remains if a couple of opcodes are missed because of
data being accidentally compiled and the compiler assuming an opcode is
the data for a false opcode, and also the problem of jump tables
and jumping to locations stored in registers.

--
Ian Farquhar                      Phone : + 61 2 805-9400
Office of Computing Services      Fax   : + 61 2 805-7433
Macquarie University  NSW  2109   Also  : + 61 2 805-7420
Australia                         EMail : ifarqhar@suna.mqcc.mq.oz.au