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From: ed@mtxinu.UUCP (Ed Gould)
Newsgroups: net.micro.68k
Subject: Re: asm construct in Alcyon-C and others
Message-ID: <581@mtxinu.UUCP>
Date: Sat, 19-Apr-86 17:11:00 EST
Article-I.D.: mtxinu.581
Posted: Sat Apr 19 17:11:00 1986
Date-Received: Mon, 21-Apr-86 07:46:56 EST
References: <293@Shasta.ARPA>
Reply-To: ed@mtxinu.UUCP (Ed Gould)
Organization: mt Xinu, Berkeley, CA
Lines: 39

>Alcyon-C, and compilers derived from the 'Portable' C compiler (at least)
>allow direct insertion of assembly statements into the compiled code.
>the syntax is:
>	asm( " any string to put into .s file ");
>
>The double quotes are mandatory, and the entire statement must appear on
>a single line.  This is processed during pass 1 of the compiler.  Any
>linkages to variables, etc., must be in conformance with the code
>generated by your compiler (look at a .s file for examples).

All true.  Note, however, that there is a bug in the 4.2BSD compiler,
and possibly other PCC derivatives as well.  I don't remember the
nature of the bug in any detail, but the workaround is to place
a null statement (extra semicolon) before the asm():

	;asm("whatever");

Of course, if this is to be included in an if (or other similar construct),
braces *must* be used:

	if(condition)
		;asm("xxx");

just won't do it!

	if(condition) {
		;asm("xxx");
	}

is required.

(It may be the case that the bug doesn't manifest itself after ifs.
I just don't remember where it matters.)

-- 
Ed Gould                    mt Xinu, 2910 Seventh St., Berkeley, CA  94710  USA
{ucbvax,decvax}!mtxinu!ed   +1 415 644 0146

"A man of quality is not threatened by a woman of equality."