LKML Archive on lore.kernel.org
 help / color / Atom feed
From: David Laight <David.Laight@ACULAB.COM>
To: 'Adrian Bunk' <bunk@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tom Stellard <tstellar@redhat.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	"Nathan Chancellor" <nathan@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Fangrui Song <maskray@google.com>,
	Serge Guelton <sguelton@redhat.com>,
	Sylvestre Ledru <sylvestre@mozilla.com>
Subject: RE: Very slow clang kernel config ..
Date: Sun, 2 May 2021 11:35:19 +0000
Message-ID: <0eba31ea508f4ec491f56e3b8c85fb6c@AcuMS.aculab.com> (raw)
In-Reply-To: <20210502093123.GC12293@localhost>

From: Adrian Bunk
> Sent: 02 May 2021 10:31
> 
> On Sat, May 01, 2021 at 09:32:25AM -0700, Linus Torvalds wrote:
> >...
> > Yes, it can save on disk use, but unless it's some very core library
> > used by a lot of things (ie particularly things like GUI libraries
> > like gnome or Qt or similar), the disk savings are often not all that
> > big - and disk is cheap. And the memory savings are often actually
> > negative (again, unless it's some big library that is typically used
> > by lots of different programs at the same time).
> >...
> > I think people have this incorrect picture that "shared libraries are
> > inherently good". They really really aren't. They cause a lot of
> > problems, and the advantage really should always be weighed against
> > those (big) disadvantages.
> >...
> 
> Disk and memory usage is not the biggest advantage.
> 
> The biggest advantage of shared libraries is that they enable
> distributions to provide security fixes.
> 
> Distributions try hard to have only one place to patch and one package
> to rebuild when a CVE has to be fixed.
> 
> It is not feasible to rebuild all users of a library in a
> distribution every time a CVE gets published for a library.

Absolutely.
You'd also need to rebuild every application that might include
the static version of the broken function.
Good luck finding all those on a big install.

OTOH just splitting a compiler into multiple shared objects
that have no other use is, as Linus said, stupid.

Building shared libraries requires the same control as building
the kernel.
The user interface mustn't change.
You can add new functions, but not change any existing ones.
This is easy in C, difficult in C++.

Since PLT lookups can only handle code, you really don't want
data areas shared between the program and library.
If the size ever changes 'horrid things (tm)' happen.

We compile any shared libraries with -fvisibility=hidden and
mark any entry points with __attribute__((visibility("protected"))).
This means that calls with a library are simple PC-relative
and only the entry points are visible outside.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-29 21:53 Linus Torvalds
2021-04-30  0:19 ` Nick Desaulniers
2021-04-30  2:22   ` Nick Desaulniers
2021-05-01  0:19     ` Nick Desaulniers
2021-05-01  0:23       ` Nick Desaulniers
2021-05-01  0:25         ` Nick Desaulniers
2021-05-01  0:40           ` Nick Desaulniers
2021-05-01  1:22           ` Linus Torvalds
2021-05-01  1:48             ` Nick Desaulniers
2021-05-01  2:16               ` Fangrui Song
2021-05-01  3:32               ` Tom Stellard
2021-05-01 16:32                 ` Linus Torvalds
2021-05-01 19:57                   ` Serge Guelton
2021-05-01 22:39                     ` Linus Torvalds
2021-05-01 23:55                       ` Fangrui Song
2021-05-01 21:58                   ` David Laight
2021-05-02  9:31                   ` Adrian Bunk
2021-05-02 11:35                     ` David Laight [this message]
2021-05-02 16:12                     ` Linus Torvalds
2021-05-02 16:45                       ` Adrian Bunk
2021-05-02 16:49                         ` Linus Torvalds
2021-05-02 17:55                           ` Adrian Bunk
2021-05-02 17:59                             ` Linus Torvalds
2021-05-02 21:48                               ` Adrian Bunk
2021-05-04 22:02                                 ` Miguel Ojeda
2021-05-05  0:58                                   ` Theodore Ts'o
2021-05-05 17:21                                     ` Miguel Ojeda
2021-05-04 21:32                     ` Miguel Ojeda
2021-05-05 11:05                       ` David Laight
2021-05-05 13:53                         ` Miguel Ojeda
2021-05-05 14:13                           ` David Laight
2021-05-05 16:06                             ` Miguel Ojeda
2021-05-05 16:25                               ` David Laight
2021-05-05 17:55                                 ` Miguel Ojeda
2021-05-03  1:03                   ` Maciej W. Rozycki
2021-05-03 14:38                     ` Theodore Ts'o
2021-05-03 14:54                       ` Theodore Ts'o
2021-05-03 17:14                         ` Maciej W. Rozycki
2021-05-03 16:09                       ` David Laight
2021-05-04 23:04                       ` Greg Stark
2021-05-05  0:55                         ` Theodore Ts'o
2021-05-01 23:37               ` Mike Hommey
2021-05-02  5:19               ` Dan Aloni
2021-05-03 16:48                 ` Tom Stellard
2021-05-03 19:00                   ` Fangrui Song
2021-04-30  0:52 ` Nathan Chancellor
2021-04-30  2:21   ` Nick Desaulniers

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=0eba31ea508f4ec491f56e3b8c85fb6c@AcuMS.aculab.com \
    --to=david.laight@aculab.com \
    --cc=bunk@kernel.org \
    --cc=clang-built-linux@googlegroups.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=masahiroy@kernel.org \
    --cc=maskray@google.com \
    --cc=nathan@kernel.org \
    --cc=ndesaulniers@google.com \
    --cc=sguelton@redhat.com \
    --cc=sylvestre@mozilla.com \
    --cc=torvalds@linux-foundation.org \
    --cc=tstellar@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git
	git clone --mirror https://lore.kernel.org/lkml/10 lkml/git/10.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git