Re: Live Patching Microconference at Linux Plumbers

From: Miroslav Benes <mbenes@suse.cz>
To: "Jose E. Marchesi" <jose.marchesi@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	jpoimboe@kernel.org, jikos@kernel.org, pmladek@suse.com,
	joe.lawrence@redhat.com, nstange@suse.de, mpdesouza@suse.de,
	broonie@kernel.org, live-patching@vger.kernel.org,
	Nick Desaulniers <ndesaulniers@google.com>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	elena.zannoni@oracle.com, indu.bhagat@oracle.com
Subject: Re: Live Patching Microconference at Linux Plumbers
Date: Fri, 14 Apr 2023 16:14:53 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LSU.2.21.2304141611090.4426@pobox.suse.cz> (raw)
In-Reply-To: <87r0sm39pt.fsf@oracle.com>

> > I'm happy to talk about the kernel-side of arm64 live patching; it'd be good to
> > get in contact with anyone looking at the arm64 userspace side (e.g.
> > klp-convert).
> >
> > I have some topics which overlap between live-patching and general toolchain
> > bits and pieces, and I'm not sure if they'd be best suited here or in a
> > toolchain track, e.g.
> >
> > * How to avoid/minimize the need to reverse-engineer control flow for things
> >   like ORC generation.
> >
> >   On the arm64 side we're pretty averse to doing this to generate metadata for
> >   unwinding (and we might not need to), but there are things objtool does today
> >   that requires awareness of control-flow (e.g. forward-edge checks for noinstr
> >   safety).
> >
> >   Hopefully without a flamewar about DWARF...
> >
> > * Better compiler support for noinstr and similar properties.
> >
> >   For example, noinstr functions are currently all noinline, and we can't
> >   inline a noinstr function into a noinstr function, leading to a painful mix
> >   of noinstr and __always_inline. Having a mechanism to allow noinstr code to
> >   be inlined into other noinstr code would be nice.
> >
> >   Likewise, whether we could somehow get compile-time warnings about unintended
> >   calls from instrumentable code from noinstr code.
> >
> > * How is this going to work with rust?
> >
> >   It's not clear to me whether/how things like ftrace, RELIABLE_STACKTRACE, and
> >   live-patching are going to work with rust. We probably need to start looking
> >   soon.
> >
> > I've Cc'd Nick, Jose, and Miguel, in case they have thoughts.
> 
> We have indeed submitted a proposal for a Toolchains MC for Plumbers.

Great.

> I think the two first topics mentioned above (CFG in ELF and handling of
> noinstr functions) would definitely fit well in the Toolchains MC.

Yes.

> As for Rust... we have the Rust GCC support and that would fit in the MC
> as well.  We can surely invite some of the hackers working in the
> front-end.  But maybe it would be better to have that discussion in a
> Rust MC, if there is gonna be one (Miguel?).

I would definitely welcome a session which Mark proposed. Be it at Live 
Patching MC or Rust MC. I know next to nothing about how Rust is wired 
into the kernel and what impact it might have on us. The sooner we 
understand possible issues, the better.

> For starters, I would make sure that the involved MCs (Live Patching,
> Toolchains, and an eventual Rust MC) do not overlap in the schedule.
> Then we could have these discussions in either microconferences.

Agreed.

Miroslav