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Path: utzoo!watmath!clyde!cbosgd!ukma!david
From: david@ukma.UUCP (David Herron, NPR Lover)
Newsgroups: net.bugs.4bsd
Subject: /lib/c2 optimizes calls instructions
Message-ID: <2064@ukma.UUCP>
Date: Sun, 18-Aug-85 21:43:46 EDT
Article-I.D.: ukma.2064
Posted: Sun Aug 18 21:43:46 1985
Date-Received: Tue, 20-Aug-85 21:22:24 EDT
Organization: U of Kentucky, Mathematical Sciences, Lexington KY
Lines: 96

Index: /lib/c2, BRL-Unix release 3, likely appears in other 4.?BSD.

Problem: Calls instructions have a format "calls <const-#-of-args>,<addr>".
	The <const-#-of-args> argument will sometimes be "optimized" into
	a register reference.  This isn't necessary, and breaks the
	massager which helps create the code in the kernel.

Repeat-by: Compile the following program segment:

	b() {}
	a()
	{
		register int i;

		i = 0;
		b();
	}

	For which you get:

LL0:
	.data
	.text
	.align	1
	.globl	_b
_b:
	.word	L12
	jbr 	L14
L15:
	ret
	.set	L12,0x0
L14:
	jbr 	L15
	.data
	.text
	.align	1
	.globl	_a
_a:
	.word	L17
	jbr 	L19
L20:
	clrl	r11
	calls	$0,_b
	ret
	.set	L17,0x800
L19:
	jbr 	L20

After running /lib/c2 -i:

.data
LL0:.data
.text
.align	1
.globl	_b
.set	L12,0x0
.data
.text
_b:.word	L12
ret
.align	1
.globl	_a
.set	L17,0x800
.data
.text
_a:.word	L17
clrl	r11
calls	r11,_b
ret


	Notice that the $0 has been changed to r11.

Fix: I was going to provide a fix, but I took one look at the code for
	c2 and decided I wasn't that brave :-).  I did notice a few
	places in c21.c which looked to be likely candidates for fixing.
	What I suggest is that c2 be taught not to optimize calls instructions.

Work-around:  Add rules to asm.sed or inline (as appropriate) to match
	all the possibilities that calls might be optimized into.
	Since this is non-trivial I would really prefer for c2 to be fixed.


Could someone who still runs 4.2BSD (and 4.3BSD too) check to see if the
bug is that widely spread?  And System V while yer at it..... :-)




-- 
--- David Herron
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Hackin's in me blood.  My mother was known as Miss Hacker before she married!