Re: [PATCH] Revert "kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled"

[Joe Lawrence]

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:
> > >
> > >  ÂÂ 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
> > >  ÂÂ 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
> > >  ÂÂ use it.
> > >
> > >  ÂÂ (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
> > >  ÂÂ 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.

Oops, lets try that again:

http://people.redhat.com/~jolawren/klp-compiler-notes/livepatch/compiler-considerations.html

-- Joe