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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Mark Brown <broonie@kernel.org>
Cc: linux-kernel@vger.kernel.org, Jiri Kosina <jikos@kernel.org>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>, Miroslav Benes <mbenes@suse.cz>,
	Petr Mladek <pmladek@suse.com>,
	linux-doc@vger.kernel.org, live-patching@vger.kernel.org,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v3] Documentation: livepatch: document reliable stacktrace
Date: Fri, 15 Jan 2021 09:16:32 -0600	[thread overview]
Message-ID: <20210115151609.lqrl2yuy2zvrcm47@treble> (raw)
In-Reply-To: <20210115142446.13880-1-broonie@kernel.org>

On Fri, Jan 15, 2021 at 02:24:46PM +0000, Mark Brown wrote:
> From: Mark Rutland <mark.rutland@arm.com>
> 
> Add documentation for reliable stacktrace. This is intended to describe
> the semantics and to be an aid for implementing architecture support for
> HAVE_RELIABLE_STACKTRACE.
> 
> Unwinding is a subtle area, and architectures vary greatly in both
> implementation and the set of concerns that affect them, so I've tried
> to avoid making this too specific to any given architecture. I've used
> examples from both x86_64 and arm64 to explain corner cases in more
> detail, but I've tried to keep the descriptions sufficient for those who
> are unfamiliar with the particular architecture.
> 
> I've tried to give rationale for all the recommendations/requirements,
> since that makes it easier to spot nearby issues, or when a check
> happens to catch a few things at once. I believe what I have written is
> sound, but as some of this was reverse-engineered I may have missed
> things worth noting.
> 
> I've made a few assumptions about preferred behaviour, notably:
> 
> * If you can reliably unwind through exceptions, you should (as x86_64
>   does).
> 
> * 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.
> 
> * 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.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Jiri Kosina <jikos@kernel.org>
> Cc: Joe Lawrence <joe.lawrence@redhat.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Miroslav Benes <mbenes@suse.cz>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: linux-doc@vgert.kernel.org
> Cc: live-patching@vger.kernel.org
> [Updates following review -- broonie]
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
> 
> v3:
>  - Incorporated objtool section from Mark.
>  - Deleted confusing notes about using annotations.

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

-- 
Josh


  reply	other threads:[~2021-01-15 15:18 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-15 14:24 [PATCH v3] Documentation: livepatch: document reliable stacktrace Mark Brown
2021-01-15 15:16 ` Josh Poimboeuf [this message]
2021-01-15 16:47 ` Mark Rutland
2021-01-15 17:12   ` Mark Brown
2021-01-15 17:20     ` Jonathan Corbet
2021-01-18 12:21       ` Mark Rutland

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