Path: utzoo!utgpu!attcan!uunet!ncrlnk!ncr-sd!hp-sdd!hplabs!ucbvax!purdue.edu!comer
From: comer@purdue.edu (Douglas Comer)
Newsgroups: comp.os.xinu
Subject: Re:  disable macro in V6 XINU
Message-ID: <8811031232.AA03013@merlin.cs.purdue.edu>
Date: 3 Nov 88 12:32:54 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 40


  >>	     I am using version 6 of Xinu on a PDP/11.  I am attempting to
  >>	     disable the interrupts and am having a few problems.
  >>	     The first question is why when you use the disable macro must
  >>	     you use the symbol ps (ie disable(ps))?

The disable macro is a kludge.  We chose it because calling a procedure is
too expensive on slow machines.  The cc11 command inserts an awk script
between the compiler and assembler to substitute correct offsets in place
of the text "~ps".  It only works with variable name "ps" because the cpp
used doesn't substitute parameters inside quoted strings.

  >>	     Where is the space
  >>	     for this symbol defined?  Why does the compiler not care if
  >>	     you did not define it in your program?

You must define	a local variable "ps" in any procedure that calls disable()
restore().

  >>	     My second question is why the statement "disable( ps)" make
  >>	     the compiler spit up with the following error: "/tmp/ctm3a###"
  >>	     followed by an "r 20" on the line immediately below it.  The
  >>	     ### represents a random number.

That's an assembler error messages (no kidding, that's what the original UNIX
C compiler used -- really short, cryptic messages).  It's a relocation error
on line 20 of the temporary file that the C compiler has produced for you.
You must have an old version of cc11 and the substitution script.  The version
of cc11 we've distributed for many years is a C program and the awk script is
updated to catch missing ps declarations and report them.  You should get the
latest version.
	
  >>	    Finally, what does the ~ tell the assembler? (ie asm("mfps ~ps"))

It means that the symbol is to be relocated wrt the local stack (i.e., it's
a local variable in the code being assembled).


Cheers,
Doug