ubuntu_bpf test failed to build on F-OEM-5.6

[Po-Hsu Lin]

Test build failed with:
    Couldn't find kernel BTF; set VMLINUX_BTF to specify its location.

Please find attachment for the complete build log.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.6.0-1010-oem 5.6.0-1010.10
ProcVersionSignature: User Name 5.6.0-1010.10-oem 5.6.8
Uname: Linux 5.6.0-1010-oem x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
Date: Mon May 18 16:03:17 2020
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=C.UTF-8
 SHELL=/bin/bash
SourcePackage: linux-signed-oem-5.6
UpgradeStatus: No upgrade log present (probably fresh install)

[Po-Hsu Lin (cypressyew)]

This is affecting the net test in ubuntu_kernel_selftests on F-OEM-5.6 as well.

[Po-Hsu Lin (cypressyew)]

Build log on jenkins is complaining about the use of unknown builtin '__builtin_preserve_field_info:

    ^
    progs/test_core_reloc_bitfields_direct.c:59:13: error: use of unknown builtin '__builtin_preserve_field_info' [-Wimplicit-function-declaration]
    out->s32 = BPF_CORE_READ_BITFIELD(in, s32);
    ^
    /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:68:36: note: expanded from macro 'BPF_CORE_READ_BITFIELD'
    const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
    ^
    /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:23:2: note: expanded from macro '__CORE_RELO'
    __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
    ^
    7 errors generated.
    llc-9: error: llc-9: :1:1: error: expected top-level entity
    BPF obj compilation failed
    ^

[Timo Aaltonen (tjaalton)]

a fix is committed to git

[Po-Hsu Lin (cypressyew)]

Issue still exist in 5.6.0-1011.11

 Warning: Kernel ABI header at 'tools/include/uapi/linux/if_link.h' differs from latest version at 'include/uapi/linux/if_link.h'
 progs/test_xdp_bpf2bpf.c:11:18: warning: unknown attribute 'preserve_access_index' ignored [-Wunknown-attributes]
 } __attribute__((preserve_access_index));
 ^
 progs/test_xdp_bpf2bpf.c:19:18: warning: unknown attribute 'preserve_access_index' ignored [-Wunknown-attributes]
 } __attribute__((preserve_access_index));
 ^
 progs/test_xdp_bpf2bpf.c:28:18: warning: unknown attribute 'preserve_access_index' ignored [-Wunknown-attributes]
 } __attribute__((preserve_access_index));
 ^
 3 warnings generated.
 progs/test_core_reloc_bitfields_direct.c:53:13: error: use of unknown builtin '__builtin_preserve_field_info' [-Wimplicit-function-declaration]
 out->ub1 = BPF_CORE_READ_BITFIELD(in, ub1);
 ^
 /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:68:36: note: expanded from macro 'BPF_CORE_READ_BITFIELD'
 const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
 ^
 /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:23:2: note: expanded from macro '__CORE_RELO'
 __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
 ^
 progs/test_core_reloc_bitfields_direct.c:54:13: error: use of unknown builtin '__builtin_preserve_field_info' [-Wimplicit-function-declaration]
 out->ub2 = BPF_CORE_READ_BITFIELD(in, ub2);
 ^
 /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:68:36: note: expanded from macro 'BPF_CORE_READ_BITFIELD'
 const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
 ^
 /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:23:2: note: expanded from macro '__CORE_RELO'
 __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
 ^
 progs/test_core_reloc_bitfields_direct.c:55:13: error: use of unknown builtin '__builtin_preserve_field_info' [-Wimplicit-function-declaration]
 out->ub7 = BPF_CORE_READ_BITFIELD(in, ub7);
 ^
 /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:68:36: note: expanded from macro 'BPF_CORE_READ_BITFIELD'
 const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
 ^
 /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:23:2: note: expanded from macro '__CORE_RELO'
 __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
 ^
 progs/test_core_reloc_bitfields_direct.c:56:13: error: use of unknown builtin '__builtin_preserve_field_info' [-Wimplicit-function-declaration]
 out->sb4 = BPF_CORE_READ_BITFIELD(in, sb4);
 ^
 /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:68:36: note: expanded from macro 'BPF_CORE_READ_BITFIELD'
 const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
 ^
 /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/test...

[Timo Aaltonen (tjaalton)]

try it with clang-10?

[Timo Aaltonen (tjaalton)]

reference:
https://lkml.org/lkml/2020/2/19/433

[Po-Hsu Lin (cypressyew)]

Test built OK with clang-10, I will see if this change can be applied to all different kernel / arch in Focal

(It's reported that the clang-10 does not work well with s390x https://kernel.ubuntu.com/git/ubuntu/autotest-client-tests.git/commit/?id=95f91d5964229e56faa7034c258e5b36b6c59b17)

[Po-Hsu Lin (cypressyew)]

The test_map test build with llvm-10 / clang-10 on Focal s390x zVM will fail with:
  libbpf: Error loading .BTF into kernel: -22.
  libbpf: Error loading BTF: Invalid argument(22)

I think I will need to make exception for 5.6 kernel on Focal.

[Timo Aaltonen (tjaalton)]

yeah, and make it default in groovy and up

[Po-Hsu Lin (cypressyew)]

On Groovy it seems clang was pointed to clang-10, so no further fixes were needed for now.