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From: Mark Brown <broonie@kernel.org>
To: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	jpoimboe@redhat.com, jthierry@redhat.com,
	catalin.marinas@arm.com, will@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 5/8] arm64: Detect an FTRACE frame and mark a stack trace unreliable
Date: Tue, 23 Mar 2021 18:27:53 +0000	[thread overview]
Message-ID: <20210323182753.GE5490@sirena.org.uk> (raw)
In-Reply-To: <bc450f09-1881-9a9c-bfbc-5bb31c01d8ce@linux.microsoft.com>


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On Tue, Mar 23, 2021 at 12:23:34PM -0500, Madhavan T. Venkataraman wrote:
> On 3/23/21 12:02 PM, Mark Rutland wrote:

> > 3. Figure out exception boundary handling. I'm currently working to
> >    simplify the entry assembly down to a uniform set of stubs, and I'd
> >    prefer to get that sorted before we teach the unwinder about
> >    exception boundaries, as it'll be significantly simpler to reason
> >    about and won't end up clashing with the rework.

> So, here is where I still have a question. Is it necessary for the unwinder
> to know the exception boundaries? Is it not enough if it knows if there are
> exceptions present? For instance, using something like num_special_frames
> I suggested above?

For reliable stack trace we can live with just flagging things as
unreliable when we know there's an exception boundary somewhere but (as
Mark mentioned elsewhere) being able to actually go through a subset of
exception boundaries safely is likely to help usefully improve the
performance of live patching, and for defensiveness we want to try to
detect during an actual unwind anyway so it ends up being a performance
improvment and double check rather than saving us code.  Better
understanding of what's going on in the presence of exceptions may also
help other users of the unwinder which can use stacks which aren't
reliable get better results.

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  parent reply	other threads:[~2021-03-23 18:29 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <5997dfe8d261a3a543667b83c902883c1e4bd270>
2021-03-15 16:57 ` [RFC PATCH v2 0/8] arm64: Implement reliable stack trace madvenka
2021-03-15 16:57   ` [RFC PATCH v2 1/8] arm64: Implement stack trace termination record madvenka
2021-03-18 15:09     ` Mark Brown
2021-03-18 20:26       ` Madhavan T. Venkataraman
2021-03-19 12:30         ` Mark Brown
2021-03-19 14:29           ` Madhavan T. Venkataraman
2021-03-19 18:19             ` Madhavan T. Venkataraman
2021-03-19 22:03               ` Madhavan T. Venkataraman
2021-03-23 10:24                 ` Mark Rutland
2021-03-23 12:39                   ` Madhavan T. Venkataraman
2021-03-15 16:57   ` [RFC PATCH v2 2/8] arm64: Implement frame types madvenka
2021-03-18 17:40     ` Mark Brown
2021-03-18 22:22       ` Madhavan T. Venkataraman
2021-03-19 13:22         ` Mark Brown
2021-03-19 14:40           ` Madhavan T. Venkataraman
2021-03-19 15:02             ` Madhavan T. Venkataraman
2021-03-19 16:20               ` Mark Brown
2021-03-19 16:27                 ` Madhavan T. Venkataraman
2021-03-23 10:34     ` Mark Rutland
2021-03-15 16:57   ` [RFC PATCH v2 3/8] arm64: Terminate the stack trace at TASK_FRAME and EL0_FRAME madvenka
2021-03-18 18:26     ` Mark Brown
2021-03-18 20:29       ` Madhavan T. Venkataraman
2021-03-23 10:36         ` Mark Rutland
2021-03-23 12:40           ` Madhavan T. Venkataraman
2021-03-15 16:57   ` [RFC PATCH v2 4/8] arm64: Detect an EL1 exception frame and mark a stack trace unreliable madvenka
2021-03-23 10:42     ` Mark Rutland
2021-03-23 12:46       ` Madhavan T. Venkataraman
2021-03-23 13:04         ` Mark Rutland
2021-03-23 13:31           ` Madhavan T. Venkataraman
2021-03-23 14:33             ` Mark Rutland
2021-03-23 15:22               ` Madhavan T. Venkataraman
2021-03-15 16:57   ` [RFC PATCH v2 5/8] arm64: Detect an FTRACE " madvenka
2021-03-23 10:51     ` Mark Rutland
2021-03-23 12:56       ` Madhavan T. Venkataraman
2021-03-23 13:36         ` Mark Rutland
2021-03-23 13:38           ` Madhavan T. Venkataraman
2021-03-23 14:15             ` Madhavan T. Venkataraman
2021-03-23 14:57               ` Mark Rutland
2021-03-23 15:26                 ` Madhavan T. Venkataraman
2021-03-23 16:20                   ` Madhavan T. Venkataraman
2021-03-23 17:02                     ` Mark Rutland
2021-03-23 17:23                       ` Madhavan T. Venkataraman
2021-03-23 17:27                         ` Madhavan T. Venkataraman
2021-03-23 18:27                         ` Mark Brown [this message]
2021-03-23 20:23                           ` Madhavan T. Venkataraman
2021-03-23 18:30                         ` Mark Rutland
2021-03-23 20:24                           ` Madhavan T. Venkataraman
2021-03-23 21:04                             ` Madhavan T. Venkataraman
2021-03-23 16:48                   ` Mark Rutland
2021-03-23 16:53                     ` Madhavan T. Venkataraman
2021-03-23 17:09                       ` Mark Rutland
2021-03-15 16:57   ` [RFC PATCH v2 6/8] arm64: Check the return PC of every stack frame madvenka
2021-03-15 16:57   ` [RFC PATCH v2 7/8] arm64: Detect kretprobed functions in stack trace madvenka
2021-03-15 16:58   ` [RFC PATCH v2 8/8] arm64: Implement arch_stack_walk_reliable() madvenka
2021-03-15 19:01   ` [RFC PATCH v2 0/8] arm64: Implement reliable stack trace Madhavan T. Venkataraman

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