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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, ardb@kernel.org, nobuta.keiya@fujitsu.com,
	sjitindarsingh@gmail.com, catalin.marinas@arm.com,
	will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com,
	jthierry@redhat.com, linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v6 3/3] arm64: Create a list of SYM_CODE functions, check return PC against list
Date: Thu, 29 Jul 2021 15:52:10 +0100	[thread overview]
Message-ID: <20210729145210.GP4670@sirena.org.uk> (raw)
In-Reply-To: <f9931a57-7a81-867b-fa2a-499d441c5acd@linux.microsoft.com>

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On Thu, Jul 29, 2021 at 09:06:26AM -0500, Madhavan T. Venkataraman wrote:
> On 7/28/21 12:25 PM, Mark Rutland wrote:
> > On Wed, Jun 30, 2021 at 05:33:56PM -0500, madvenka@linux.microsoft.com wrote:

> > Since some of the above is speculative (e.g. the bit about optprobes),
> > and as code will change over time, I think we should have a much terser
> > comment, e.g.

> > 	/*
> > 	 * As SYM_CODE functions don't follow the usual calling
> > 	 * conventions, we assume by default that any SYM_CODE function
> > 	 * cannot be unwound reliably.
> > 	 *
> > 	 * Note that this includes exception entry/return sequences and
> > 	 * trampoline for ftrace and kprobes.
> > 	 */

> Just to confirm, are you suggesting that I remove the entire large comment
> detailing the various cases and replace the whole thing with the terse comment?
> I did the large comment because of Mark Brown's input that we must be verbose
> about all the cases so that it is clear in the future what the different
> cases are and how we handle them in this code. As the code evolves, the comments
> would evolve.

I do agree with Mark that this has probably gone from one extreme to the
other and could be cut back a lot - originally it didn't reference there
being complicated cases like the trampoline at all IIRC so you needed
external knowledge to figure out that those cases were handled.

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WARNING: multiple messages have this Message-ID (diff)
From: Mark Brown <broonie@kernel.org>
To: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com,
	sjitindarsingh@gmail.com, catalin.marinas@arm.com,
	will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com,
	jthierry@redhat.com, linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v6 3/3] arm64: Create a list of SYM_CODE functions, check return PC against list
Date: Thu, 29 Jul 2021 15:52:10 +0100	[thread overview]
Message-ID: <20210729145210.GP4670@sirena.org.uk> (raw)
In-Reply-To: <f9931a57-7a81-867b-fa2a-499d441c5acd@linux.microsoft.com>


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On Thu, Jul 29, 2021 at 09:06:26AM -0500, Madhavan T. Venkataraman wrote:
> On 7/28/21 12:25 PM, Mark Rutland wrote:
> > On Wed, Jun 30, 2021 at 05:33:56PM -0500, madvenka@linux.microsoft.com wrote:

> > Since some of the above is speculative (e.g. the bit about optprobes),
> > and as code will change over time, I think we should have a much terser
> > comment, e.g.

> > 	/*
> > 	 * As SYM_CODE functions don't follow the usual calling
> > 	 * conventions, we assume by default that any SYM_CODE function
> > 	 * cannot be unwound reliably.
> > 	 *
> > 	 * Note that this includes exception entry/return sequences and
> > 	 * trampoline for ftrace and kprobes.
> > 	 */

> Just to confirm, are you suggesting that I remove the entire large comment
> detailing the various cases and replace the whole thing with the terse comment?
> I did the large comment because of Mark Brown's input that we must be verbose
> about all the cases so that it is clear in the future what the different
> cases are and how we handle them in this code. As the code evolves, the comments
> would evolve.

I do agree with Mark that this has probably gone from one extreme to the
other and could be cut back a lot - originally it didn't reference there
being complicated cases like the trampoline at all IIRC so you needed
external knowledge to figure out that those cases were handled.

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  reply	other threads:[~2021-07-29 14:52 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <3f2aab69a35c243c5e97f47c4ad84046355f5b90>
2021-06-30 22:33 ` [RFC PATCH v6 0/3] arm64: Implement stack trace reliability checks madvenka
2021-06-30 22:33   ` madvenka
2021-06-30 22:33   ` [RFC PATCH v6 1/3] arm64: Improve the unwinder return value madvenka
2021-06-30 22:33     ` madvenka
2021-07-28 16:56     ` Mark Rutland
2021-07-28 16:56       ` Mark Rutland
2021-07-29 13:54       ` Madhavan T. Venkataraman
2021-07-29 13:54         ` Madhavan T. Venkataraman
2021-06-30 22:33   ` [RFC PATCH v6 2/3] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-06-30 22:33     ` madvenka
2021-06-30 22:33   ` [RFC PATCH v6 3/3] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-06-30 22:33     ` madvenka
2021-07-28 17:25     ` Mark Rutland
2021-07-28 17:25       ` Mark Rutland
2021-07-29 14:06       ` Madhavan T. Venkataraman
2021-07-29 14:06         ` Madhavan T. Venkataraman
2021-07-29 14:52         ` Mark Brown [this message]
2021-07-29 14:52           ` Mark Brown
2021-07-29 17:07           ` Madhavan T. Venkataraman
2021-07-29 17:07             ` Madhavan T. Venkataraman
2021-07-29 15:48         ` Mark Rutland
2021-07-29 15:48           ` Mark Rutland
2021-07-29 16:27           ` Mark Brown
2021-07-29 16:27             ` Mark Brown
2021-07-29 17:09           ` Madhavan T. Venkataraman
2021-07-29 17:09             ` Madhavan T. Venkataraman
2021-07-26 13:49   ` [RFC PATCH v6 0/3] arm64: Implement stack trace reliability checks Madhavan T. Venkataraman
2021-07-26 13:49     ` Madhavan T. Venkataraman
2021-08-12 13:24 ` [RFC PATCH v7 0/4] arm64: Reorganize the unwinder and implement " madvenka
2021-08-12 13:24   ` madvenka
2021-08-12 13:24   ` [RFC PATCH v7 1/4] arm64: Make all stack walking functions use arch_stack_walk() madvenka
2021-08-12 13:24     ` madvenka
2021-08-12 15:23     ` Mark Brown
2021-08-12 15:23       ` Mark Brown
2021-08-12 16:30       ` Madhavan T. Venkataraman
2021-08-12 16:30         ` Madhavan T. Venkataraman
2021-08-12 20:59     ` kernel test robot
2021-08-12 13:24   ` [RFC PATCH v7 2/4] arm64: Reorganize the unwinder code for better consistency and maintenance madvenka
2021-08-12 13:24     ` madvenka
2021-08-12 13:24   ` [RFC PATCH v7 3/4] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-08-12 13:24     ` madvenka
2021-08-12 13:24   ` [RFC PATCH v7 4/4] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-08-12 13:24     ` madvenka
2021-08-12 18:53     ` kernel test robot
2021-08-12 18:31   ` [RFC PATCH v7 0/4] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman
2021-08-12 18:31     ` Madhavan T. Venkataraman
2021-08-12 18:45     ` Madhavan T. Venkataraman
2021-08-12 18:45       ` Madhavan T. Venkataraman
2021-08-12 18:35 ` madvenka
2021-08-12 18:35   ` madvenka
2021-08-12 18:35   ` [RFC PATCH v7 1/4] arm64: Make all stack walking functions use arch_stack_walk() madvenka
2021-08-12 18:35     ` madvenka
2021-08-12 18:35   ` [RFC PATCH v7 2/4] arm64: Reorganize the unwinder code for better consistency and maintenance madvenka
2021-08-12 18:35     ` madvenka
2021-08-12 18:35   ` [RFC PATCH v7 3/4] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-08-12 18:35     ` madvenka
2021-08-12 18:35   ` [RFC PATCH v7 4/4] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-08-12 18:35     ` madvenka

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