Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/17/84 chuqui version 1.9 3/12/85; site unisoft.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!harvard!seismo!lll-crg!dual!unisoft!fnf
From: fnf@unisoft.UUCP
Newsgroups: net.emacs
Subject: Re: GNU on Integrated Solutions
Message-ID: <561@unisoft.UUCP>
Date: Sun, 8-Sep-85 14:08:56 EDT
Article-I.D.: unisoft.561
Posted: Sun Sep  8 14:08:56 1985
Date-Received: Tue, 10-Sep-85 04:07:12 EDT
References: <34700009@ctvax>
Reply-To: fnf@unisoft.UUCP (Fred Fish)
Organization: UniSoft Systems, Berkeley
Lines: 42

In article <34700009@ctvax> pedz@ctvax writes:
>
>3) alloca not only has the same problem on the IS as on the other
>68000 systems but it has one much more serious problem.  The IS
>compiler does the link and then movm to save the registers.  Thus when
>the stack pointer is moved down, the registers are popped back off
>with the movm get bad values from the alloca storage...

Hmm, I don't know what the IS compiler is doing but both our 5.0 compiler
(based on the mit port of the pcc) and our 5.2 compiler (the SGS from the
generic 68000 microport), use the *frame pointer* with the link and movem
instructions, not the *stack pointer*.  Thus mucking with the stack pointer
has no effect on subroutine linkages or register save/restores.

Here is a copy of alloca.s that we use with our GNU emacs port under
SVR2 on a dual systems machine.  It seems to work fine.  Whether or
not it is correct is another matter :-).

-Fred

	file	"alloca.s"
	global	alloca
alloca:
	mov.l	(%sp)+,%a1	# pop return addr from top of stack
	mov.l	(%sp)+,%d0	# pop size in bytes from top of stack
	add.l	&R%1,%d0	# round size up to long word
	and.l	&-4,%d0		# mask out lower two bits of size
	sub.l	%d0,%sp		# allocate by moving stack pointer
	tst.b	P%1(%sp)	# stack probe to allocate pages
	mov.l	%sp,%a0		# return pointer as pointer
	mov.l	%sp,%d0		# return pointer as int to avoid disaster
	add.l	&-4,%sp		# new top of stack
	jmp	(%a1)		# not a normal return
	set	S%1,64		# safety factor for C compiler scratch
	set	R%1,3+S%1	# add to size for rounding
	set	P%1,-132	# probe this far below current top of stack


===========================================================================
Fred Fish    UniSoft Systems Inc, 739 Allston Way, Berkeley, CA  94710  USA
{ucbvax,dual}!unisoft!fnf	(415) 644 1230 		TWX 11 910 366-2145
===========================================================================