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From: rwhite@nusdhub.UUCP (Robert C. White Jr.)
Newsgroups: comp.lang.c
Subject: Re: Types
Message-ID: <117@nusdhub.UUCP>
Date: Fri, 9-Oct-87 13:33:39 EDT
Article-I.D.: nusdhub.117
Posted: Fri Oct  9 13:33:39 1987
Date-Received: Sun, 11-Oct-87 17:38:13 EDT
References: <7264@brl-adm.ARPA> <734@sdchema.sdchem.UUCP> <293@osupyr.UUCP> <384@mcdsun.UUCP>
Organization: National University, San Diego
Lines: 40
Summary: Linking Assembler.

In article <384@mcdsun.UUCP>, fnf@mcdsun.UUCP (Fred Fish) writes:
> 	the linker fix up all the jumps that are really "near" jumps
> 	to be "near" jumps.  In either case, you either grow or
> 	shrink the code as appropriate, in the linker.  What could
> 	be easier?  In either case, you end up with exactly the same
> 	executable object code.  No nops, no "non-optimal" jumps, the
> 	*same* *optimal* *code*.

	First, a linker is a "linking loader" and it's only REAL
purpose is to resolve refrences and setup dynamic relocation
information.  ALL "short" jumps [add/subtract value from the
instruction pointer directly] are compleetly generated and closed
in the assembler.  If there were to be an alteration in the size
of a block of code-text, the linker would have to "reassemble" the
code block to make up for the altered "short" jumps and such.  In
order for the linker to do this it would either need the source
code, or it would have to take a stab at disassembeling the object
code and hope not to get it wrong.
	The assembler is designed to AUTOMATICALLY determine the
"near"ness or "far"ness of a refrence.  This works beautfuly as
long as you act like a pascal programmer and only use backward
refrences.  For the forward refrences you must use a keyword like
"near" or "far" or else take what you get, and hope what you get
is close enough to work.
	It should be obvious that the assemblers job is to assemble
and the linkers job is to link.

MR FRED:  At one point you said "what could be simpler" [deleted from this text
for brevity].  If it is so simple, I would love to see your compleeted
disassembling-assebeling-optomizing-editing-linking-loader on the
market.  [For a PC or 3B2 prefreable, as these are the machines
I have avalible to test it on.]

Discalmer:  YES! I used x86 refrences, I did this because I like to
stick to topics and machines I know, so _PLEASE_, no "there are other
machines in existance, you introverted slob..." type flames.  And, yes,
I am woking on my spelling, but if I waited till my dislexic brain
could do it perfectly, nobody would ever see my deathless prose.

Rob ("So who asked you anyway?") white.