Re: [RFC bpf-next 5/6] bpf: selftests: test_tunnel: Disable CO-RE relocations

[Daniel Xu]

On Fri, Oct 27, 2023 at 01:33:09PM -0700, Andrii Nakryiko wrote:
> On Fri, Oct 27, 2023 at 11:46 AM Daniel Xu <dxu@xxxxxxxxx> wrote:
> >
> > Switching to vmlinux.h definitions seems to make the verifier very
> > unhappy with bitfield accesses. The error is:
> >
> >     ; md.u.md2.dir = direction;
> >     33: (69) r1 = *(u16 *)(r2 +11)
> >     misaligned stack access off (0x0; 0x0)+-64+11 size 2
> >
> > It looks like disabling CO-RE relocations seem to make the error go
> > away.
> >
> 
> for accessing bitfields libbpf provides
> BPF_CORE_READ_BITFIELD_PROBED() and BPF_CORE_READ_BITFIELD() macros

In this case the code in question is:

        __u8 direction = 0;
        md.u.md2.dir = direction;

IOW the problem is assigning to bitfields, not reading from them.

Is that something that libbpf needs to support as well?

Thanks,
Daniel