On Thu, Nov 11, 2021 at 07:34:38AM IST, Vinicius Costa Gomes wrote:
> Hi Kartikeya,
>
> Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> writes:
>
> > On Thu, Nov 11, 2021 at 05:21:53AM IST, Vinicius Costa Gomes wrote:
> >> Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes:
> >>
> >> >> Thanks for the fix.
> >> >>
> >> >> But instead of moving this to core.c, you can probably make the btf.h
> >> >> declaration conditional on CONFIG_BPF_SYSCALL, since this is not useful in
> >> >> isolation (only used by verifier for module kfunc support). For the case of
> >> >> kfunc_btf_id_list variables, just define it as an empty struct and static
> >> >> variables, since the definition is still inside btf.c. So it becomes a noop for
> >> >> !CONFIG_BPF_SYSCALL.
> >> >>
> >> >> I am also not sure whether BTF is useful without BPF support, but maybe I'm
> >> >> missing some usecase.
> >> >
> >> > Unlikely. I would just disallow such config instead of sprinkling
> >> > the code with ifdefs.
> >>
> >> Is something like this what you have in mind?
> >>
> >> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> >> index 6fdbf9613aec..eae860c86e26 100644
> >> --- a/lib/Kconfig.debug
> >> +++ b/lib/Kconfig.debug
> >> @@ -316,6 +316,7 @@ config DEBUG_INFO_BTF
> >> bool "Generate BTF typeinfo"
> >> depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
> >> depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
> >> + depends on BPF_SYSCALL
> >> help
> >> Generate deduplicated BTF type information from DWARF debug info.
> >> Turning this on expects presence of pahole tool, which will convert
> >>
> >>
> >
> > BTW, you will need a little more than that, I suspect the compiler optimizes out
> > the register/unregister call so we don't see a build failure, but adding a side
> > effect gives me errors, so something like this should resolve the problem (since
> > kfunc_btf_id_list variable definition is behind CONFIG_BPF_SYSCALL).
> >
> > diff --git a/include/linux/btf.h b/include/linux/btf.h
> > index 203eef993d76..e9881ef9e9aa 100644
> > --- a/include/linux/btf.h
> > +++ b/include/linux/btf.h
> > @@ -254,6 +254,8 @@ void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
> > struct kfunc_btf_id_set *s);
> > bool bpf_check_mod_kfunc_call(struct kfunc_btf_id_list *klist, u32 kfunc_id,
> > struct module *owner);
> > +extern struct kfunc_btf_id_list bpf_tcp_ca_kfunc_list;
> > +extern struct kfunc_btf_id_list prog_test_kfunc_list;
> > #else
> > static inline void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
> > struct kfunc_btf_id_set *s)
> > @@ -268,13 +270,13 @@ static inline bool bpf_check_mod_kfunc_call(struct kfunc_btf_id_list *klist,
> > {
> > return false;
> > }
> > +struct kfunc_btf_id_list {};
> > +static struct kfunc_btf_id_list bpf_tcp_ca_kfunc_list __maybe_unused;
> > +static struct kfunc_btf_id_list prog_test_kfunc_list __maybe_unused;
> > +
> > #endif
> >
> > #define DEFINE_KFUNC_BTF_ID_SET(set, name) \
> > struct kfunc_btf_id_set name = { LIST_HEAD_INIT(name.list), (set), \
> > THIS_MODULE }
> > -
> > -extern struct kfunc_btf_id_list bpf_tcp_ca_kfunc_list;
> > -extern struct kfunc_btf_id_list prog_test_kfunc_list;
> > -
> > #endif
> >
>
> I could not reproduce the build failure here even when adding some side
> effects, but I didn't try very hard.
>
> As you are more familiar with the code, I would be glad if you could
> take it from here and propose a patch.
>
Sure, no worries!
>
> Cheers,
> --
> Vinicius
--
Kartikeya
