On Wed, Nov 11, 2015 at 03:00:44PM +0100, Miroslav Benes wrote: > > Background: Why does livepatch need to write its own relocations? > > == > > A typical livepatch module contains patched versions of functions that can > > reference non-exported global symbols and non-included local symbols. > > Relocations referencing these types of symbols cannot be left in as-is > > since the kernel module loader cannot resolve them and will therefore > > reject the livepatch module. Furthermore, we cannot apply relocations that > > affect modules not loaded yet at run time (e.g. a patch to a driver). The > > current kpatch build system therefore solves this problem by embedding > > special "dynrela" (dynamic reloc) sections in the resulting patch module > > elf output. Using these dynrela sections, livepatch can correctly resolve > > symbols while taking into account its scope and what module the symbol > > belongs to, and then manually apply the dynamic relocations. > > I'll only add that we solve the problem with kallsyms calls in kGraft. It > can get really cumbersome from time to time, so this work would simplify > our effort as well. I haven't yet reviewed the code in-depth, but overall I think this patch set is a good idea. It simplifies livepatch itself as well as the patch creation process (for both kGraft and kpatch-build), so it's a win-win. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
