Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!eecae!tank!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: Question about linking files
Message-ID: <16546@mimsy.UUCP>
Date: 26 Mar 89 16:10:37 GMT
References: <18925@iuvax.cs.indiana.edu> <16541@mimsy.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 40

In article <16541@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
>Given that the pANS does not have the concept of a `library', or
>even of `separate compilation', ...

I should probably rephrase that.  It does have something called
`external linkage'; it just does not tie it specifically to `separate
compilation' and `libraries'.  (The difference is that between what
must be and what usually is.)

I should also restate my point, which is this: You cannot tell which
functions are needed---consider the program

	main()
	{
		while (the_machine_continues_to_exist())
			/* void */;
		/* never gets here */
		library_function_f();
		exit(0);
	}

---so the best you can do is an approximation (`the function strftime
will never be called; the function strcpy might be called; ...').
Unfortunately, unless the link file format has been carefully defined
and the compiler cooperates, you cannot even do that:

	_foo:	.globl	_foo
		.word	0
		movl	$_foo+foosize,r0
		calls	$0,(r0)
		ret
		.align	2
	0:	.set	foosize,0b-_foo

The VAX-assembly-code function foo() calls whichever function is
linked immediately following it, so eliding that function because it
appears unused changes the execution.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris