Re: [PATCH bpf-next 1/3] selftests/bpf: Use cpu_number only on arches that have it

[Ilya Leoshkevich <iii@linux.ibm.com>]

On Tue, 2021-10-12 at 05:56 +0200, Andrii Nakryiko wrote:
> On Tue, Oct 12, 2021 at 4:51 AM Ilya Leoshkevich <iii@linux.ibm.com>
> wrote:
> > 
> > cpu_number exists only on Intel and aarch64, so skip the test
> > involing
> > it on other arches. An alternative would be to replace it with an
> > exported non-ifdefed primitive-typed percpu variable from the
> > common
> > code, but there appears to be none.
> > 
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> > ---
> >  tools/testing/selftests/bpf/prog_tests/btf_dump.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/bpf/prog_tests/btf_dump.c
> > b/tools/testing/selftests/bpf/prog_tests/btf_dump.c
> > index 87f9df653e4e..12f457b6786d 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/btf_dump.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/btf_dump.c
> > @@ -778,8 +778,10 @@ static void test_btf_dump_struct_data(struct
> > btf *btf, struct btf_dump *d,
> >  static void test_btf_dump_var_data(struct btf *btf, struct
> > btf_dump *d,
> >                                    char *str)
> >  {
> > +#if defined(__i386__) || defined(__x86_64__) ||
> > defined(__aarch64__)
> >         TEST_BTF_DUMP_VAR(btf, d, NULL, str, "cpu_number", int,
> > BTF_F_COMPACT,
> >                           "int cpu_number = (int)100", 100);
> > +#endif
> 
> We are in the talks about supporting cross-compilation of selftests,
> and this will be just another breakage that we'll have to undo.

Why would this break? Cross-compilation should define these macros
based on target, not build system.

> Can we find some other variable that will be available on all
> architectures? Maybe "runqueues"?

Wouldn't runqueues be pointless? We already have cpu_profile_flip. I
thought the idea here was to have something marked with
EXPORT_PER_CPU_SYMBOL.

> >         TEST_BTF_DUMP_VAR(btf, d, NULL, str, "cpu_profile_flip",
> > int, BTF_F_COMPACT,
> >                           "static int cpu_profile_flip = (int)2",
> > 2);
> >  }
> > --
> > 2.31.1