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From: info-mac@uw-beaver
Newsgroups: fa.info-mac
Subject: Re: high byte of address question
Message-ID: <494@uw-beaver>
Date: Thu, 24-Jan-85 01:14:03 EST
Article-I.D.: uw-beave.494
Posted: Thu Jan 24 01:14:03 1985
Date-Received: Fri, 25-Jan-85 05:20:22 EST
Sender: daemon@uw-beaver
Organization: U of Washington Computer Science
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From: John W. Peterson <JW-Peterson@UTAH-20.ARPA>

The reason the high byte of an address gets trashed in SumacC code is a
side-effect of the Sumacc relocation scheme.  Unlike the Lisa/Workshop Pascal
compiler, Sumacc does not generate position independant code.  Since the C
compiler and loader have no way of knowing where the code will be loaded (this
is decided dynamicly by the Mac memory manager), addresses are resolved every
time a Sumacc program starts up.

To resolve addresses at startup time, Sumacc uses a "clever" scheme of
run-length encoding relocation info into the high order byte of addresses
that need relocating.  The gory details of how this works can be found
by looking in crtmac.s in the Sumacc lib/ subdirectory.
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