Path: utzoo!mnetor!uunet!husc6!think!bloom-beacon!oberon!skat.usc.edu!blarson
From: blarson@skat.usc.edu (Bob Larson)
Newsgroups: comp.lang.misc
Subject: Re: HLLs vs asm (was Re: portable "asm")
Message-ID: <7924@oberon.USC.EDU>
Date: 28 Mar 88 20:02:10 GMT
References: <11702@brl-adm.ARPA> <243@eagle_snax.UUCP> <1988Mar27.002601.17038@utzoo.uucp>
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Reply-To: blarson@skat.usc.edu (Bob Larson)
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In article <1988Mar27.002601.17038@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:

>> > plus it allows access to the "bare
>> >metal", etc.)

>> Are we talking about the same language?

>Probably.  One of C's strengths -- and a major reason for its popularity --
>is that it *does* let you get at much of the underlying machine if you
>really want to *and* understand your implementation in detail.

AND your machine happens to match C fairly well AND your implimentation
does a straitforward mapping.

>  It's not
>enough to understand C and the machine, you have to understand the mapping
>between them that the compiler provides.  But once you do, you can use C
>to do most of the things an assembler can do.

This can be said of most high level languages.

>  C insists on managing the stack and some of the registers itself,

?some?  Are you implying that there are C implementations that use the
register keyword for anything other than a promise not to take the
address? :-)

> places constraints on what you
>you can do to the PC, and won't generate funny instructions for you,

Does this include the funny instructions added for use by the C
compiler? :-)  (Prime expended their 32i mode instruction set into
32ix mode mainly for use by the C compiler.)

> but
>these limitations often aren't a problem.  Otherwise it opens the machine
>up pretty thoroughly, *if* you know what you're doing.

C opens up an idea of what a machine could look like.  Not all
machines look like that.  Some machines have basic concepts difficult
or impossible to express in C.  (Such as a dec 10/20 "byte pointer"
[variable size bytes])

C is a high level language that closely models some common
architectures.  It is a mistake to think it can be used for "access to
the 'bare metal'" without specifying what 'bare metal' you are
thinking of.  (Not all the world is a vax or pdp11 or 68k or spark.)

-- 
Bob Larson	Arpa: Blarson@Ecla.Usc.Edu	blarson@skat.usc.edu
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