Re: announcing LLpatch: arch-independent live-patch creation

[Peter Swain <swine@pobox.com>]

(apologies for re-post, having trouble enforcing no-HTML mode in gmail)

On Fri, Aug 27, 2021 at 9:08 AM Evgenii Shatokhin <eshatokhin@virtuozzo.com>
wrote:
> LLpatch requires a pre-built kernel tree ("repository"), right?
Yes.
It doesn't rebuild existing *.o as a pre-image of the patched code, as
kpatch does.
But LLpatch does use the dependency analysis the previous make left in
*.o.cmd, although the same information could also be extracted by "make -n
-W changed_file ..."

> Does that mean that the kernel should be built with clang first?
> Or, perhaps, clang is only used when building the patch itself, while
> the kernel can be built with GCC or other compiler used by the given
> Linux distro?
We haven't explored this deeply, as all our kernels are clang-built.
In principle this should work with gcc-built kernels, as long as the
particular change doesn't intersect with some feature which is expressed
differently between the gcc/clang worlds, such as some ELF section names.
But as there are so many such potential incompatibilities, we do not
recommend this.
As a precondition for LLpatch-patchable kernels, I would recommend moving
to clang-built base kernels