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Error loading xdp program that worked with bpf_load

Jesper Dangaard Brouer
 

(Cross-posting to iovisor-dev)

Seeking input from BPF-llvm developers. How come Clang/LLVM 10+ is
generating incompatible BTF-info in ELF file, and downgrading to LLVM-9
fixes the issue ?

On Wed, 10 Jun 2020 14:50:27 -0700 Elerion <elerion1000@...> wrote:

Never mind, I fixed it by downgrading to Clang 9.

It appears to be an issue with Clang/LLVM 10+

https://github.com/cilium/ebpf/issues/43

On Wed, Jun 10, 2020 at 2:38 PM Toke Høiland-Jørgensen <toke@...> wrote:

Elerion <elerion1000@...> writes:

[69] FUNC xdp_program type_id=68 vlen != 0
'vlen != 0' is the error. Not sure why you hit that; what's the output
of 'bpftool btf dump file yourprog.o' ?

-Toke
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer

Andrii Nakryiko
 

On Thu, Jun 11, 2020 at 4:00 AM Jesper Dangaard Brouer
<@NetOptimizer> wrote:

(Cross-posting to iovisor-dev)

Seeking input from BPF-llvm developers. How come Clang/LLVM 10+ is
generating incompatible BTF-info in ELF file, and downgrading to LLVM-9
fixes the issue ?


On Wed, 10 Jun 2020 14:50:27 -0700 Elerion <elerion1000@...> wrote:

Never mind, I fixed it by downgrading to Clang 9.

It appears to be an issue with Clang/LLVM 10+

https://github.com/cilium/ebpf/issues/43
This is newer Clang recording that function is global, not static.
libbpf is sanitizing BTF to remove this flag, if kernel doesn't
support this. But given this is re-implementation of libbpf, that's
probably not happening, right?


On Wed, Jun 10, 2020 at 2:38 PM Toke Høiland-Jørgensen <toke@...> wrote:

Elerion <elerion1000@...> writes:

[69] FUNC xdp_program type_id=68 vlen != 0
'vlen != 0' is the error. Not sure why you hit that; what's the output
of 'bpftool btf dump file yourprog.o' ?

-Toke

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer

Alexei Starovoitov
 

On Thu, Jun 11, 2020 at 9:35 AM Andrii Nakryiko
<andrii.nakryiko@...> wrote:

On Thu, Jun 11, 2020 at 4:00 AM Jesper Dangaard Brouer
<@NetOptimizer> wrote:

(Cross-posting to iovisor-dev)

Seeking input from BPF-llvm developers. How come Clang/LLVM 10+ is
generating incompatible BTF-info in ELF file, and downgrading to LLVM-9
fixes the issue ?


On Wed, 10 Jun 2020 14:50:27 -0700 Elerion <elerion1000@...> wrote:

Never mind, I fixed it by downgrading to Clang 9.

It appears to be an issue with Clang/LLVM 10+

https://github.com/cilium/ebpf/issues/43
This is newer Clang recording that function is global, not static.
libbpf is sanitizing BTF to remove this flag, if kernel doesn't
support this. But given this is re-implementation of libbpf, that's
probably not happening, right?
just running ./test_xdp_veth.sh on the latest bpf-next with the latest
clang I see:
BTF debug data section '.BTF' rejected: Invalid argument (22)!
- Length: 514
Verifier analysis:
...
[11] VAR _license type_id=9 linkage=1
[12] DATASEC license size=0 vlen=1 size == 0


BTF debug data section '.BTF' rejected: Invalid argument (22)!
- Length: 494
Verifier analysis:
...
[11] VAR _license type_id=9 linkage=1
[12] DATASEC license size=0 vlen=1 size == 0


BTF debug data section '.BTF' rejected: Invalid argument (22)!
11] VAR _license type_id=9 linkage=1
[12] DATASEC license size=0 vlen=1 size == 0

PING 10.1.1.33 (10.1.1.33) 56(84) bytes of data.
64 bytes from 10.1.1.33: icmp_seq=1 ttl=64 time=0.042 ms

--- 10.1.1.33 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.042/0.042/0.042/0.000 ms
selftests: xdp_veth [PASS]

Is that just the noise from libbpf probing or what?

Andrii Nakryiko
 

On Thu, Jun 11, 2020 at 1:41 PM Elerion <elerion1000@...> wrote:

I am using libbpf from here https://github.com/libbpf/libbpf I'm not
using ebpf. I just linked to the ebpf issue because it seems like the
only thing related to this problem when I googled it.
Ok, that I can help with, then.

What's the kernel version? Where I can find repro? Steps, etc.
Basically, a bit more context would help, as I wasn't part of initial
discussion.



On Thu, Jun 11, 2020 at 9:34 AM Andrii Nakryiko
<andrii.nakryiko@...> wrote:

On Thu, Jun 11, 2020 at 4:00 AM Jesper Dangaard Brouer
<@NetOptimizer> wrote:

(Cross-posting to iovisor-dev)

Seeking input from BPF-llvm developers. How come Clang/LLVM 10+ is
generating incompatible BTF-info in ELF file, and downgrading to LLVM-9
fixes the issue ?


On Wed, 10 Jun 2020 14:50:27 -0700 Elerion <elerion1000@...> wrote:

Never mind, I fixed it by downgrading to Clang 9.

It appears to be an issue with Clang/LLVM 10+

https://github.com/cilium/ebpf/issues/43
This is newer Clang recording that function is global, not static.
libbpf is sanitizing BTF to remove this flag, if kernel doesn't
support this. But given this is re-implementation of libbpf, that's
probably not happening, right?


On Wed, Jun 10, 2020 at 2:38 PM Toke Høiland-Jørgensen <toke@...> wrote:

Elerion <elerion1000@...> writes:

[69] FUNC xdp_program type_id=68 vlen != 0
'vlen != 0' is the error. Not sure why you hit that; what's the output
of 'bpftool btf dump file yourprog.o' ?

-Toke

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer