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:
>
> http://file.bos.redhat.com/~jolawren/klp-compiler-notes/livepatch/compiler-considerations.html
Hi Joe,
The notes link you shared is not accessible.
Regards,
--
Kamalesh
