mailing list of musl libc
 help / color / mirror / code / Atom feed
From: Rich Felker <dalias@libc.org>
To: Arnd Bergmann <arnd@kernel.org>
Cc: musl@lists.openwall.com, Markus Wichmann <nullplan@gmx.net>,
	Florian Weimer <fweimer@redhat.com>
Subject: Re: [musl] Backwards kernel compatibility
Date: Wed, 2 Jun 2021 10:56:33 -0400	[thread overview]
Message-ID: <20210602145632.GC13220@brightrain.aerifal.cx> (raw)
In-Reply-To: <CAK8P3a2MDvXCQGbjcUiXZko8yWgn+r1Gc0G6ajYG08m41ibY8g@mail.gmail.com>

On Wed, Jun 02, 2021 at 01:52:43PM +0200, Arnd Bergmann wrote:
> On Wed, Jun 2, 2021 at 9:38 AM Martin Vajnar <martin.vajnar@gmail.com> wrote:
> >
> > Hi Rich,
> >
> > thank you for such detailed reply.> Cc: <stable@vger.kernel.org>
> > Cc: Martin Vajnar <martin.vajnar@gmail.com>
> > Cc: musl@lists.openwall.com
> > Acked-by: Will Deacon <will.deacon@arm.com>
> > Signed-off-by: Michael Weiser <michael.weiser@gmx.de>
> > Signed-off-by: Will Deacon <will.deacon@arm.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > This was backported to v4.14 and later, but is missing in v4.4 and
> > before, apparently because of a trivial merge conflict. This is
> > a manual backport I did after I saw a report about the issue
> > by Martin Vajnar on the musl mailing list.
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> >  arch/arm64/kernel/traps.c | 8 --------
> >  1 file changed, 8 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> > index 9322be69ca09..db4163808c76 100644
> > --- a/arch/arm64/kernel/traps.c
> > +++ b/arch/arm64/kernel/traps.c
> > @@ -363,14 +363,6 @@ asmlinkage long do_ni_syscall(struct pt_regs *regs)
> >         }
> >  #endif
> >
> > -       if (show_unhandled_signals && printk_ratelimit()) {
> > -               pr_info("%s[%d]: syscall %d\n", current->comm,
> > -                       task_pid_nr(current), (int)regs->syscallno);
> > -               dump_instr("", regs);
> > -               if (user_mode(regs))
> > -                       __show_regs(regs);
> > -       }
> > -
> >         return sys_ni_syscall();
> >  }
> >
> > --
> > 2.29.2
> >
> >
> > út 25. 5. 2021 v 0:00 odesílatel Rich Felker <dalias@libc.org> napsal:
> > >
> > > On Mon, May 24, 2021 at 03:52:44PM +0200, Martin Vajnar wrote:
> > > > Hi, Markus,
> > > >
> > > > sorry for the late reply it was quite busy lately. You're describing
> > > > exactly the issue, we are facing in our project. We need to use old kernel
> > > > which we have only in binary form and have headers for it. At the same time
> > > > we would like to have the latest musl running on it.
> > > >
> > > > The problem we encounter is that for unsupported (or better said, not
> > > > supported yet) syscalls we get performance overhead because of the ENOSYS.
> > >
> > > Can you give some information on what syscalls these are and if/how
> > > you measured the performance overhead as being significant?
> >
> >
> > The main source of overhead comes from the kernel 4.4 which on arm64
> > produces stack traces when not implemented syscall is invoked:
> >
> >     https://github.com/torvalds/linux/blob/afd2ff9b7e1b367172f18ba7f693dfb62bdcb2dc/arch/arm64/kernel/traps.c#L369
> 
> That is clearly a bug that was fixed in mainline and backported to linux-4.14
> but not 4.4 or 4.9. I've sent a manual backport for inclusion in those kernels
> now.

Is this practical to hotpatch into kernels on devices that aren't
readily upgradable?

Rich

  reply	other threads:[~2021-06-02 14:56 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10  5:50 Martin Vajnar
2021-05-10  6:46 ` Florian Weimer
2021-05-10 18:58 ` Markus Wichmann
2021-05-24 13:52   ` Martin Vajnar
2021-05-24 22:00     ` Rich Felker
2021-06-02  7:38       ` Martin Vajnar
2021-06-02 11:52         ` Arnd Bergmann
2021-06-02 14:56           ` Rich Felker [this message]
2021-06-02 16:01             ` Arnd Bergmann
2021-06-02 16:18               ` Arnd Bergmann
2021-06-09  7:03           ` Arnd Bergmann
2021-06-08 22:16       ` Martin Vajnar
2021-06-09  0:37         ` Rich Felker

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=20210602145632.GC13220@brightrain.aerifal.cx \
    --to=dalias@libc.org \
    --cc=arnd@kernel.org \
    --cc=fweimer@redhat.com \
    --cc=musl@lists.openwall.com \
    --cc=nullplan@gmx.net \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://git.vuxu.org/mirror/musl/

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).