Re: [PATCH v3 8/9] objtool/klp: Fix relocations for EXPORT_SYMBOL_FOR_MODULES() symbols

[Song Liu]

On Fri, Aug 7, 2026 at 2:38 PM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
>
> EXPORT_SYMBOL_FOR_MODULES() puts a symbol in a "module:<names>"
> namespace, which the module loader grants access to by matching the
> importing module's name against that list.
>
> klp_reloc_needed() only creates a klp reloc for module-owned exports; a
> vmlinux export gets a normal reloc.  For a vmlinux symbol exported with
> EXPORT_SYMBOL_FOR_MODULES(), using a normal reloc results in a modpost
> failure in klp-build:
>
>   ERROR: modpost: module livepatch-foo uses symbol mpol_shared_policy_lookup from namespace module:kvm, but does not import it.
>
> And the modpost error is correct: even with that error removed, the
> patch module would fail to load:
>
>   livepatch_foo: module uses symbol (mpol_shared_policy_lookup) from namespace module:kvm, but does not import it.
>   livepatch_foo: Unknown symbol mpol_shared_policy_lookup (err -22)
>
> Treat it like an unexported symbol by using a klp reloc.
>
> Note this only affects "module:" namespaces.  Ordinary namespaced
> exports continue to work with normal relocs thanks to copy_import_ns(),
> which propagates the patched object's import_ns tags to the patch
> module.
>
> Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
> Reported-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
> Link: https://lore.kernel.org/6a6608f4-0a05-4d75-8b7f-edddfac9c5d4@xxxxxxxxxx
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

Acked-by: Song Liu <song@xxxxxxxxxx>