Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!utah-gr!uplherc!esunix!bpendlet
From: bpendlet@esunix.UUCP (Bob Pendleton)
Newsgroups: comp.arch
Subject: Re: Software Distribution
Message-ID: <970@esunix.UUCP>
Date: 15 Sep 88 15:01:45 GMT
References: <1988Sep7.210317.5781@utzoo.uucp>
Organization: Evans & Sutherland, Salt Lake City, Utah
Lines: 48

From article <1988Sep7.210317.5781@utzoo.uucp>, by henry@utzoo.uucp (Henry Spencer):
> In article <963@esunix.UUCP> bpendlet@esunix.UUCP (Bob Pendleton) writes:
> 
> Distribution with sources is Good.  Distribution without sources is Evil.

Oh, great... GOOD versus EVIL! Send me your definition of good and
evil and how you feel about absolute moral values and I'll send you
mine. Then we can debate the whole issue. But PLEASE do it off line.
I've found that very few people are much interested in these kinds of
debates. 

>>68020. But, you can make it run without error if those contraints are
>>available to the target machine code generator...
> 
> You miss my point.  36-bit ints can be dealt with in the software fairly
> well.  What I'm thinking of is much more subtle things that the compiler
> can't easily discover and put in the intermediate form, e.g. "this program
> depends on being able to dereference NULL pointers".  Or, for that matter,
> "the details of the arithmetic in this program assume that integers are
> at least 36 bits".  This is the sort of thing that will not be known to
> the compiler unless the programmer is explicit about it -- and lack of
> programmer attention to such details is exactly the problem.

I've addressed this problem in another posting, but what the hey, I'll
do it again. To be truely portable the intermediate form MUST address
the issues you mention. Even if the source language doesn't define the
semantics of dereferencing NULL pointers, the intermediate form must
define the semantics of dereferencing NULL pointers. Otherwise, just
as C code that counts on being able to dereference NULL pointers is
not fully portable, an intermediate form that doesn't define the
semantics of dereferencing NULL pointers will not be fully portable.

No matter what the source language, a compiler that generates a
portable intermediate form will have to explicitly state the
assumptions it is making about things like word size, arithmetic, and
the semantics of dereferencing NULL pointers, or conform to the
semantics defined for these things in the portable intermediate form.
Otherwise it just won't work.

Yes, that means that C compilers will have to put information into the
intermediate form that does not derive from any programmer provided
declarations. That indicates a flaw in C, not a problem with the idea
of a portable intermediate language. 

			Bob P.-- 
Bob Pendleton @ Evans & Sutherland
UUCP Address:  {decvax,ucbvax,allegra}!decwrl!esunix!bpendlet
Alternate:     utah-cs!esunix!bpendlet
        I am solely responsible for what I say.