linux-kernel - Re: [PATCH v4] Documentation: livepatch: document reliable stacktrace

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Date:   Mon, 18 Jan 2021 17:50:54 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        Jiri Kosina <jikos@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Miroslav Benes <mbenes@...e.cz>, linux-doc@...r.kernel.org,
        live-patching@...r.kernel.org, Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v4] Documentation: livepatch: document reliable stacktrace

Hi Petr,

On Mon, Jan 18, 2021 at 03:02:31PM +0100, Petr Mladek wrote:
> On Fri 2021-01-15 17:16:17, Mark Brown wrote:
> > I've made a few assumptions about preferred behaviour, notably:
> > 
> > * If you can reliably unwind through exceptions, you should (as x86_64
> >   does).

IIRC this was confirmed as desireable, and the text already reflects
this.

> > * It's fine to omit ftrace_return_to_handler and other return
> >   trampolines so long as these are not subject to patching and the
> >   original return address is reported. Most architectures do this for
> >   ftrace_return_handler, but not other return trampolines.

Likewise I think we agreed this was fine, given these were not
themselves subkect to patching.

> > * For cases where link register unreliability could result in duplicate
> >   entries in the trace or an inverted trace, I've assumed this should be
> >   treated as unreliable. This specific case shouldn't matter to
> >   livepatching, but I assume that that we want a reliable trace to have
> >   the correct order.

I don't think we had any comments either way on this, but I think it's
sane to say this for now and later relax it if we need to.

... so I reckon we can just delete all this as Josh suggests. Any acks
for the patch itself tacitly agrees with these points. :)

Thanks,
Mark.