Xref: utzoo comp.unix.sysv386:9133 alt.sources:3920
Path: utzoo!utgpu!cs.utexas.edu!uunet!pdn!tscs!tct!chip
From: chip@tct.com (Chip Salzenberg)
Newsgroups: comp.unix.sysv386,alt.sources
Subject: Bug in SCO 3.2v2 memmove(), and fix
Message-ID: <285FBE64.468B@tct.com>
Date: 19 Jun 91 20:28:20 GMT
Organization: Teltronics/TCT, Sarasota, FL
Lines: 112

SCO's memmove() function in the 3.2v2 development system libc.a
library has an insidious bug: it trashes the EBX register.  This
register is used to hold register variables.  I suspect the bug crept
in due to a simple-minded translation of a '286 routine, because on
the '286, BX need not be preserved.

The fix is to replace memmove.o in /lib/libc.a with the version
included below.  Note that if you use profiling, you must also put a
profiling version of memmove() in /usr/lib/libp/libc.a.

To assemble the non-profiling version:

    as -m -o memmove.o memmove.s

To assemble the profiling verson:

    as -m -o memmove_p.o profile.s memmove.s

(How strange that this bug has gone unnoticed for so long...)

#! /bin/sh
# This is a shell archive.  Remove anything before this line, then unpack
# it by saving it into a file and typing "sh file".  To overwrite existing
# files, type "sh file -c".  You can also feed this as standard input via
# unshar, or by typing "sh <file", e.g..  If this archive is complete, you
# will see the following message at the end:
#		"End of shell archive."
# Contents:  profile.s memmove.s
# Wrapped by chip@count on Wed Jun 19 16:24:17 1991
PATH=/bin:/usr/bin:/usr/ucb ; export PATH
if test -f 'profile.s' -a "${1}" != "-c" ; then 
  echo shar: Will not clobber existing file \"'profile.s'\"
else
echo shar: Extracting \"'profile.s'\" \(139 characters\)
sed "s/^X//" >'profile.s' <<'END_OF_FILE'
X/ $Id: profile.s,v 1.1 1990/12/18 09:07:04 chip Exp $
X/
X/ Prefix file for turning on assembler profiling.
X/
X
Xdefine(`PROFILE',``PROFILE'')
END_OF_FILE
if test 139 -ne `wc -c <'profile.s'`; then
    echo shar: \"'profile.s'\" unpacked with wrong size!
fi
# end of 'profile.s'
fi
if test -f 'memmove.s' -a "${1}" != "-c" ; then 
  echo shar: Will not clobber existing file \"'memmove.s'\"
else
echo shar: Extracting \"'memmove.s'\" \(687 characters\)
sed "s/^X//" >'memmove.s' <<'END_OF_FILE'
X/ $Id: memmove.s,v 1.3 1991/06/05 19:15:44 chip Exp $
X/
X/ Implementation of memmove(), which is inexplicably missing
X/ from the SCO Unix C library.
X/
X
X	.globl	memmove
Xmemmove:
Xifdef(`PROFILE',`
X	.bss
X.L1:	.=.+4
X	.text
X	mov	$.L1,%edx
X	.globl	_mcount
X	call	_mcount
X')
X	push	%edi
X	push	%esi
X	mov	12(%esp),%edi
X	mov	16(%esp),%esi
X	mov	20(%esp),%ecx
X	mov	%edi,%eax		/ return value: dest
X	jcxz	mm_exit
X
X	mov	%edi,%edx
X	sub	%esi,%edx
X	jb	mm_simple
X	cmp	%edx,%ecx
X	jb	mm_simple
X
X	add	%ecx,%edi
X	dec	%edi
X	add	%ecx,%esi
X	dec	%esi
X	std
X	rep; movsb
X	cld
X	jmp	mm_exit
X
Xmm_simple:
X	cld
X	mov	%ecx,%edx
X	shr	$2,%ecx
X	rep; movs
X	mov	%edx,%ecx
X	and	$3,%ecx
X	rep; movsb
X
Xmm_exit:
X	pop	%esi
X	pop	%edi
X	ret
END_OF_FILE
if test 687 -ne `wc -c <'memmove.s'`; then
    echo shar: \"'memmove.s'\" unpacked with wrong size!
fi
# end of 'memmove.s'
fi
echo shar: End of shell archive.
exit 0