Subject: debian-policy: Policy proposal: Cpu extension code
Package: debian-policy
Version: 3.1.1.1
Severity: wishlist
Greetings! I posted this proposal to debian-policy for discussion in
June, but am only now formally requesting its inclusion in the
policy. I've taken the liberty of including recommendations from
various submitters.
The goal of this proposal is to provide a mechanism whereby packages
can safely make use of cpu instruction set extensions
(e.g. sse1,sse2,3dnow,3dnowext, etc.) In this scheme, packages can
install on any machine of the general architecture, and extension
instructions only get executed on appropriately capable cpus, even if
/usr is served up over NFS.
Proposal outline:
1) All packages providing programs and/or libraries which make use of
CPU instruction set extensions (CISEs) must provide identical functionality
on all machines of the given general architecture. One way to
achieve this is for the code to be protected by runtime probes of
the cpu, followed by appropriate branching to correctly executable
sections. Alternatively, packages can separate routines using
CISEs into shared libraries. This section of the policy details the
machanism whereby ldso will load appropriate versions of such
libraries according to the capabilities of the runtime cpu.
2) Libraries containing CSIEs should be placed in a designated subdir
of /usr/lib specialized for code requiring the cpu extension in
question. All such directories should be agreed upon and sanctioned
by the policy committee. As a suggestion, the directory might be
named after the cpu capability (as reported in /proc/cpuinfo) required
to run the code, (e.g. /usr/lib/{sse,sse2,3dnow,3dnowext} on i386,
/usr/lib/ev5 on alpha, and perhaps /usr/lib/sparc64 on sparc, etc.)
3) All functionality provided by this code should also be provided by
a binary-equivalent generic shared lib of the same name and soname
in /usr/lib.
4) Ideally, ldso should be smart enough to search the special
directories first given the running cpu characteristics. Barring
this, a system script, update-ld.so.conf, should be created, which
packages can call at install/remove time, to add/remove the
specialized paths appropriate to the running cpu to /etc/ld.so.conf
and then run ldconfig. Optionally (and
preferably), this script could also be run at boot time to catch
cpu-upgrades and/or kernel upgrades (SSE requires kernel support).
Paths need not be added, and can be removed, if no libraries exist in
the directory. The package providing this script should be in the
'base' section if invoked at boot time. Otherwise, packages using
this functionality should depend upon the update-ld.so.conf package.
5) For this scheme to work, it is necessary to ensure that ldso loads
libraries in the directories specified in /etc/ld.so.conf in
preference to identically named versions in /lib or /usr/lib, as is
currently the case with Debian's ldso. It is part of this policy
that such behavior remain standard on Debian systems.
The Debian atlas packages currently use this scheme. I believe that
at least gmp can currently make use of it as well. I've provided a
sample update-ld.so.conf below. If this proposal is accepted, I'd be
happy to package it or something similar.
Thanks for your work on Debian!
--
Camm Maguire [EMAIL PROTECTED]
==========================================================================
"The earth is but one country, and mankind its citizens." -- Baha'u'llah
=============================================================================
sample update-ld.so.conf, can doubtlessly be improved
=============================================================================
#!/bin/bash
set -e
FILE=/etc/ld.so.conf
usage() {
echo "Usage: $0 [ --enable <ext> ] [ --disable <ext> ] [ --auto ]"
exit 1
}
do_ldso() {
local j=$@ jj=$@ p q qp qm i k zi pp tf
tf=$(tempfile -m 644)
( while read p; do
q=$(basename $p)
qp="+$q"
qm="_$q"
k=""
for i in $j ; do
if [ $i = $qp ] ; then
k=p
break
fi
if [ $i = $qm ] ; then
k=m
break
fi
done
case $k in
p) pp=""
zi=""
for i in $jj; do
if [ -z $zi ] && echo $i | grep -q "^+"
; then
echo /usr/lib/${i#+}
else
pp="$pp $i"
fi
if [ $i = $qp ] ; then zi=t ; fi
done
jj=$pp
;;
m) ;;
*) echo $p;;
esac
done < $FILE
for i in $jj; do
if echo $i | grep -q "^+" ; then
echo /usr/lib/${i#+}
fi
done
) >$tf
mv $tf $FILE
ldconfig
}
cpu_probe_i386() {
local fl i res kv j
if ! [ -r /proc/cpuinfo ] ; then
echo This script needs the proc filesystem to work
exit 1
fi
fl=$(grep ^flags /proc/cpuinfo)
kv=$(uname -a | cut -f3 -d\ | cut -f2 -d.)
#
# Names changed in 2.4.x
# Listed possibilities must be in order of preference here
#
case $kv in
2) ss="26 xmm 3dnowext 3dnow";;
*) ss="sse2 sse 3dnowext 3dnow";;
esac
res=""
for i in $ss; do
j=${i/xmm/sse}
j=${j/26/sse2}
if echo $fl | grep -q "\<$i\>" ; then
res="$res +$j"
else
res="$res _$j"
fi
done
echo $res
}
cpu_probe_alpha() {
local fl i res j
if ! [ -r /proc/cpuinfo ] ; then
echo This script needs the proc filesystem to work
exit 1
fi
fl=$(grep ^"cpu model" /proc/cpuinfo)
res=""
for i in EV7 EV6 EV5; do
j=${i/EV7/ev5}
j=${j/EV6/ev5}
if grep -q "\<$i\>" $fl ; then
res="$res +$j"
else
res="$res -$j"
fi
done
echo $res
}
cpu_probe_sparc() {
local fl i res
if ! [ -r /proc/cpuinfo ] ; then
echo This script needs the proc filesystem to work
exit 1
fi
fl=$(grep ^"cpu" /proc/cpuinfo)
res=""
for i in $fl; do
case $i in
UltraSparc) res="$res sparc64";;
*);;
esac
done
echo $res
}
mmatch() {
local k t j i
k=$1
t=""
shift
j=$@
for i in $j; do
if [ $k = ${i#?} ] ; then
t=$i;
fi
done
echo $t
}
off() {
local k j t i
k=$1
shift
j=$@
t=""
for i in $j ; do
if [ $k = ${i#?} ] ; then
t="$t _$k"
else
t="$t $i"
fi
done
echo $t
}
on() {
local k j t i
k=$1
shift
j=$@
t=""
for i in $j ; do
if [ $k = ${i#?} ] ; then
t="$t +$k"
else
t="$t $i"
fi
done
echo $t
}
AUTO=""
EN=""
DIS=""
EXT=""
if [ $# -lt 1 ] ; then
usage;
fi
case $1 in
--auto) AUTO=t; if [ $# -ne 1 ] ; then usage; fi;;
--enable) EN=t; if [ $# -ne 2 ] ; then usage; fi; EXT=$2;;
--disable) DIS=t; if [ $# -ne 2 ] ; then usage; fi; EXT=$2;;
*) usage;;
esac
ARCH=$(dpkg --print-architecture)
case $ARCH in
i386) cpu=$(cpu_probe_i386);;
alpha) cpu=$(cpu_probe_alpha);;
sparc) cpu=$(cpu_probe_sparc);;
*) echo "There are no cpu extensions supported for this architecture
($ARCH)";
exit 0;;
esac
if [ "$AUTO" = "" ] ; then
if [ "$(mmatch $EXT $cpu)" != "+$EXT" ] ; then
echo "Cpu extension $EXT is not supported on this architecture
($ARCH)"
exit 1
fi
ldso=""
while read p ; do
q=$(basename $p)
ldso="$ldso +$q"
done < $FILE
final=""
for i in $cpu ; do
t="_${i#?}"
for j in $ldso ; do
if [ $i = $j ] ; then
t=$j
fi
done
final="$final $t"
done
if [ "$EN" != "" ] ; then
final=$(on $EXT $final)
else
final=$(off $EXT $final)
fi
fi
do_ldso $final
exit 0
=============================================================================
-- System Information
Debian Release: 2.2
Kernel Version: Linux intech19 2.2.19-gen #1 SMP Fri May 25 15:14:23 EDT 2001
i686 unknown
