On Tue, Nov 16, 2021 at 4:48 PM Matteo Croce <mcroce@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, Nov 12, 2021 at 6:02 AM Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
> >
> > From: Alexei Starovoitov <ast@xxxxxxxxxx>
> >
> > v1->v2:
> > . Refactor uapi to pass 'struct bpf_core_relo' from LLVM into libbpf and further
> > into the kernel instead of bpf_core_apply_relo() bpf helper. Because of this
> > change the CO-RE algorithm has an ability to log error and debug events through
> > the standard bpf verifer log mechanism which was not possible with helper
> > approach.
> > . #define RELO_CORE macro was removed and replaced with btf_member_bit_offset() patch.
> >
> > This set introduces CO-RE support in the kernel.
> > There are several reasons to add such support:
> > 1. It's a step toward signed BPF programs.
> > 2. It allows golang like languages that struggle to adopt libbpf
> > to take advantage of CO-RE powers.
> > 3. Currently the field accessed by 'ldx [R1 + 10]' insn is recognized
> > by the verifier purely based on +10 offset. If R1 points to a union
> > the verifier picks one of the fields at this offset.
> > With CO-RE the kernel can disambiguate the field access.
> >
>
> Great, I tested the same code which was failing with the RFC series,
> now there isn't any error.
> This is the output with pr_debug() enabled:
>
> root@debian64:~/core# ./core
> [ 5.690268] prog '(null)': relo #-2115894237: kind <(null)>
> (163299788), spec is
> [ 5.690272] prog '(null)': relo #-2115894246: (null) candidate #-2115185528
> [ 5.690392] prog '(null)': relo #2: patched insn #208 (LDX/ST/STX)
> off 208 -> 208
> [ 5.691045] prog '(efault)': relo #-2115894237: kind <(null)>
> (163299788), spec is
> [ 5.691047] prog '(efault)': relo #-2115894246: (null) candidate
> #-2115185528
> [ 5.691148] prog '(efault)': relo #3: patched insn #208
> (LDX/ST/STX) off 208 -> 208
> [ 5.692456] prog '(null)': relo #-2115894237: kind <(null)>
> (163302708), spec is
> [ 5.692459] prog '(null)': relo #-2115894246: (null) candidate #-2115185668
> [ 5.692564] prog '(null)': relo #2: patched insn #104 (LDX/ST/STX)
> off 104 -> 104
> [ 5.693179] prog '(efault)': relo #-2115894237: kind <(null)>
> (163299788), spec is
> [ 5.693181] prog '(efault)': relo #-2115894246: (null) candidate
> #-2115185528
> [ 5.693258] prog '(efault)': relo #3: patched insn #208
> (LDX/ST/STX) off 208 -> 208
> [ 5.696141] prog '(null)': relo #-2115894237: kind <(null)>
> (163302708), spec is
> [ 5.696143] prog '(null)': relo #-2115894246: (null) candidate #-2115185668
> [ 5.696255] prog '(null)': relo #2: patched insn #104 (LDX/ST/STX)
> off 104 -> 104
> [ 5.696733] prog '(efault)': relo #-2115894237: kind <(null)>
> (163299788), spec is
> [ 5.696734] prog '(efault)': relo #-2115894246: (null) candidate
> #-2115185528
> [ 5.696833] prog '(efault)': relo #3: patched insn #208
> (LDX/ST/STX) off 208 -> 208
All the logged values are completely wrong, some corruption somewhere.
But I tried to see it for myself and I couldn't figure out how to get
these logs with lskel. How did you get the above?
Alexei, any guidance on how to get those verifier logs back with
test_progs? ./test_progs -vvv didn't help, I also checked trace_pipe
output, it was empty. I thought that maybe verifier truncates logs on
success and simulated failed prog validation, but still nothing.
>
> And the syscall returns success:
>
> bpf(BPF_PROG_TEST_RUN, {test={prog_fd=4, retval=0, data_size_in=0,
> data_size_out=0, data_in=NULL, data_out=NULL, repeat=0, duration=0,
> ctx_size_in=68, ctx_size_out=0, ctx_in=0x5590b97dd2a0, ctx_out=NULL}},
> 160) = 0
>
> Regards,
> --
> per aspera ad upstream
