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From: scotty@l5comp.UUCP (Scott Turner)
Newsgroups: comp.sys.amiga
Subject: Re: Difference in Aztec and Lattice Executables
Message-ID: <114@l5comp.UUCP>
Date: Sat, 9-May-87 22:18:11 EDT
Article-I.D.: l5comp.114
Posted: Sat May  9 22:18:11 1987
Date-Received: Sun, 10-May-87 11:43:42 EDT
References: <8705080053.AA10033@cory.Berkeley.EDU>
Reply-To: scotty@l5comp.UUCP (Scott Turner)
Organization: L5 Computing, Edmonds, WA
Lines: 27
Summary: Why Manx doesn't use BSS

In article <8705080053.AA10033@cory.Berkeley.EDU> dillon@CORY.BERKELEY.EDU (Matt Dillon) writes:
>	I've noticed that Lattice uses a BSS hunk for BSS data in its 
>executables, where as Aztec places it in the DATA hunk by specifying a
>larger buffer for the DATA hunk in the table section of the HEADER
>hunk than the actual DATA hunk contains.
The reason for this lies with the fact that Manx wished to access their global
data and variables via disp(A4) addressing. The AmigaDOG loader "scatter loads"
hunks into memory. Thus you can't assume that DATA and BSS hunks will follow
each other in memory. So they crammed their BSS in with their DATA.

They also didn't want to give up the space savings from using the BSS concept.
So, they make the table entry larger than the actual size so that when the
loader loads the data hunk it will allocate enough space for the data & the BSS,
WITHOUT taking up space for the BSS on the disk! Cute. The side-effect is that
they must zero the BSS themselves which they do with a hard coded ram zeroing
routine in their main startup code.

They are also in effect exploiting a bug in the loader :-). It could be argued
that the loader should check that the table size matched with the hunk size to
make sure that the code file wasn't mangled.

Scott Turner

L5 Computing, the home of Merlin, Arthur, Excalibur and the CRAM.
GEnie: JST | UUCP: stride!l5comp!scotty | 12311 Maplewood Ave; Edmonds WA 98020
If Motorola had wanted us to use BPTR's they'd have built in shifts on A regs
[ BCPL? Just say *NO*! ] (I don't smoke, send flames to /dev/null)