On 07/06/2023 11:19 am, Jan Beulich wrote: > On 07.06.2023 11:17, Roger Pau Monné wrote: >> On Wed, Jun 07, 2023 at 11:10:27AM +0200, Jan Beulich wrote: >>> On 07.06.2023 11:01, Roger Pau Monne wrote: >>>> Guard it with CONFIG_LIVEPATCH. Note alternatives are applied at boot >>>> using _apply_alternatives(). >>>> >>>> Signed-off-by: Roger Pau Monné <roger....@citrix.com> >>>> Reviewed-by: Julien Grall <jgr...@amazon.com> >>> Reviewed-by: Jan Beulich <jbeul...@suse.com> >>> albeit the implicit ack therein is only on the assumption that (apart >>> from me) it is generally deemed better ... >>> >>>> --- a/xen/arch/x86/alternative.c >>>> +++ b/xen/arch/x86/alternative.c >>>> @@ -358,11 +358,12 @@ static void init_or_livepatch >>>> _apply_alternatives(struct alt_instr *start, >>>> } >>>> } >>>> >>>> -void init_or_livepatch apply_alternatives(struct alt_instr *start, >>>> - struct alt_instr *end) >>>> +#ifdef CONFIG_LIVEPATCH >>> ... to have the #ifdef than the init_or_livepatch attribute. >> But the init_or_livepatch attribute doesn't remove the function when >> !CONFIG_LIVEPATCH, > Yes up to here. > >> so it's not a replacement for the ifdef. > That depends how you look at it. We don't meaningfully care about a > few extra bytes in .init.text, I think. So it really is the Misra > requirement of not having unreferenced symbols which makes the > difference here.
A different option, which I've recommended before for other reasons, is to build with function/data sections (already supported for livepatch), and use --gc-sections at link time. That would remove examples like this from the final binary, and there's probably wiggle-room at the MISRA level to say "we comply with this because the linker deletes it". ~Andrew
