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
next prev parent 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
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