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Date: Wed, 2 Jun 2021 10:56:33 -0400
From: Rich Felker <dalias@...c.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: musl@...ts.openwall.com, Markus Wichmann <nullplan@....net>,
Florian Weimer <fweimer@...hat.com>
Subject: Re: Backwards kernel compatibility
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@...il.com> wrote:
> >
> > Hi Rich,
> >
> > thank you for such detailed reply.> Cc: <stable@...r.kernel.org>
> > Cc: Martin Vajnar <martin.vajnar@...il.com>
> > Cc: musl@...ts.openwall.com
> > Acked-by: Will Deacon <will.deacon@....com>
> > Signed-off-by: Michael Weiser <michael.weiser@....de>
> > Signed-off-by: Will Deacon <will.deacon@....com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Signed-off-by: Arnd Bergmann <arnd@...db.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@...db.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@...c.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
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