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Bug#120418: marked as done (Policy for code using CPU extensions)

Your message dated Fri, 11 Aug 2017 12:44:51 -0700
with message-id <87o9rlx51o.fsf@iris.silentflame.com>
and subject line Closing inactive Policy bugs
has caused the Debian Bug report #120418,
regarding Policy for code using CPU extensions
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
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-- 
120418: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=120418
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message --- 
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			     			camm@enhanced.com
==========================================================================
"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

--- End Message ---
--- Begin Message --- 
control: user debian-policy@packages.debian.org
control: usertag -1 +obsolete
control: tag -1 +wontfix

Russ Allbery and I did a round of in-person bug triage at DebConf17 and
we are closing this bug as inactive.

The reasons for closing fall into the following categories, from most
frequent to least frequent:

- issue is appropriate for Policy, there is a consensus on how to fix
  the problem, but preparing the patch is very time-consuming and no-one
  has volunteered to do it, and we do not judge the issue to be
  important enough to keep an open bug around;

- issue is appropriate for Policy but there does not yet exist a
  consensus on what should change, and no recent discussion.  A fresh
  discussion might allow us to reach consensus, and the messages in the
  old bug are unlikely to help very much; or

- issue is not appropriate for Policy.

If you feel this bug is still relevant and want to restart the
discussion, you can re-open the bug.  However, please consider instead
opening a new bug with a message that summarises and condenses the
previous discussion, updates the report for the current state of Debian,
and makes clear exactly what you think should change.

A lot of these old bugs have long side tangents and numerous messages,
and that old discussion is not necessarily helpful for figuring out what
Debian Policy should say today.

-- 
Sean Whitton

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