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From: Joe Lawrence <>
To: Kamalesh Babulal <>,
	Josh Poimboeuf <>,
	Peter Zijlstra <>,
	Randy Dunlap <>
Subject: Re: [PATCH] Revert "kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled"
Date: Mon, 20 Jul 2020 07:47:43 -0400
Message-ID: <> (raw)
In-Reply-To: <>

On 7/20/20 4:50 AM, Kamalesh Babulal wrote:
> On 20/07/20 9:05 am, Joe Lawrence wrote:
>> On 7/17/20 2:29 PM, Josh Poimboeuf wrote:
>>> Use of the new -flive-patching flag was introduced with the following
>>> commit:
>>>     43bd3a95c98e ("kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled")
>>> This flag has several drawbacks:
>>> [ ... snip ... ]
>>> - While there *is* a distro which relies on this flag for their distro
>>>     livepatch module builds, there's not a publicly documented way to
>>>     create safe livepatch modules with it.  Its use seems to be based on
>>>     tribal knowledge.  It serves no benefit to those who don't know how to
>>>     use it.
>>>     (In fact, I believe the current livepatch documentation and samples
>>>     are misleading and dangerous, and should be corrected.  Or at least
>>>     amended with a disclaimer.  But I don't feel qualified to make such
>>>     changes.)
>> FWIW, I'm not exactly qualified to document source-based creation either, however I have written a few of the samples and obviously the kselftest modules.
>> The samples should certainly include a disclaimer (ie, they are only for API demonstration purposes!) and eventually it would be great if the kselftest modules could guarantee their safety as well.  I don't know quite yet how we can automate that, but perhaps some kind of post-build sanity check could verify that they are in fact patching what they intend to patch.
>> As for a more general, long-form warning about optimizations, I grabbed Miroslav's LPC slides from a few years back and poked around at some IPA-optimized disassembly... Here are my notes that attempt to capture some common cases:
> Hi Joe,
> The notes link you shared is not accessible.

Oops, lets try that again:

-- Joe

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 18:29 Josh Poimboeuf
2020-07-20  3:35 ` Joe Lawrence
2020-07-20  8:50   ` Kamalesh Babulal
2020-07-20 11:47     ` Joe Lawrence [this message]
2020-07-21 11:27   ` Miroslav Benes
2020-07-21 11:17 ` Miroslav Benes
2020-08-06  9:24   ` Petr Mladek

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