Re: Trying the bpf trace a bpf xdp program

[Yonghong Song <yhs@fb.com>]

On 12/2/19 8:34 AM, Eelco Chaudron wrote:
> 
> 
> On 29 Nov 2019, at 17:52, Yonghong Song wrote:
> 
>> On 11/29/19 8:30 AM, Eelco Chaudron wrote:
>>>
>>>
>>> On 28 Nov 2019, at 20:47, Alexei Starovoitov wrote:
>>>
>>>> On Thu, Nov 28, 2019 at 11:16 AM Eelco Chaudron <echaudro@redhat.com>
>>>> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 28 Nov 2019, at 19:18, Alexei Starovoitov wrote:
>>>>>
>>>>>> On Thu, Nov 28, 2019 at 9:20 AM Eelco Chaudron <echaudro@redhat.com>
>>>>>> wrote:
>>>>>>>
>>>>>>> Trying out the BPF trace to trace a BPF program, but I’m already
>>>>>>> getting stuck loading the object with the fexit  :(
>>>>>>
>>>>>> I can take a look after holidays.
>>>>>
>>>>> Enjoy the Holidays!! I figured out my auto kernel install script 
>>>>> failed
>>>>> whiteout me noticing, and I was running an old kernel :(
>>>>>
>>>>> I will try tomorrow with the correct kernel…
>>>>
>>>> Please also check that you have the latest llvm and pahole.
>>>> pahole version should be >= 1.13.
>>>> clang ideally from master.
>>>> If all that is working then downgrade one by one and bisect whether
>>>> the bug is.
>>>>
>>>
>>> I tried it with the latest kernel loaded but still I got some errors on
>>> bpf_object__load_xattr():
>>>
>>> $ sudo ./xdp_sample_fentry_fexit_user
>>> libbpf: Cannot find bpf_func_info for main program sec
>>> fexit/xdp_prog_simple. Ignore all bpf_func_info.
>>> libbpf: load bpf program failed: Operation not permitted
>>> libbpf: failed to load program 'fexit/xdp_prog_simple'
>>> libbpf: failed to load object './xdp_sample_fentry_fexit_kern.o'
>>> ERROR: Failed to load object file: Operation not permitted
>>>
>>>
>>> With strace:
>>>
>>> [vagrant@xdp-tutorial tracing05-xdp-fentry]$ sudo
>>> /home/vagrant/strace/strace -e bpf ./xdp_sample_fentry_fexit_user
>>> bpf(BPF_PROG_GET_FD_BY_ID, {prog_id=36, next_id=0, open_flags=0}, 
>>> 120) = 3
>>> bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_SOCKET_FILTER, insn_cnt=2,
>>> insns=0x7ffcaedfd4f0, license="GPL", log_level=0, log_size=0,
>>> log_buf=NULL, kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0,
>>> prog_name="", prog_ifindex=0,
>>> expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0,
>>> func_info_rec_size=0, func_info=NULL, func_info_cnt=0,
>>> line_info_rec_size=0, line_info=NULL, line_info_cnt=0}, 120) = 5
>>> bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_SOCKET_FILTER, insn_cnt=2,
>>> insns=0x7ffcaedfd4f0, license="GPL", log_level=0, log_size=0,
>>> log_buf=NULL, kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0,
>>> prog_name="test", prog_ifindex=0,
>>> expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0,
>>> func_info_rec_size=0, func_info=NULL, func_info_cnt=0,
>>> line_info_rec_size=0, line_info=NULL, line_info_cnt=0}, 120) = 5
>>> bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_ARRAY, key_size=4,
>>> value_size=32, max_entries=1, map_flags=0, inner_map_fd=0, map_name="",
>>> map_ifindex=0, btf_fd=0, btf_key_type_id=0, btf_value_type_id=0}, 
>>> 120) = 5
>>> bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_SOCKET_FILTER, insn_cnt=5,
>>> insns=0x7ffcaedfd490, license="GPL", log_level=0, log_size=0,
>>> log_buf=NULL, kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0,
>>> prog_name="", prog_ifindex=0,
>>> expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0,
>>> func_info_rec_size=0, func_info=NULL, func_info_cnt=0,
>>> line_info_rec_size=0, line_info=NULL, line_info_cnt=0}, 120) = 6
>>> bpf(BPF_BTF_LOAD,
>>> {btf="\237\353\1\0\30\0\0\0\0\0\0\0000\0\0\0000\0\0\0\t\0\0\0\1\0\0\0\0\0\0\1"..., 
>>>
>>> btf_log_buf=NULL, btf_size=81, btf_log_size=0, btf_log_level=0}, 120) 
>>> = 5
>>> bpf(BPF_BTF_LOAD,
>>> {btf="\237\353\1\0\30\0\0\0\0\0\0\08\0\0\08\0\0\0\t\0\0\0\0\0\0\0\0\0\0\1"..., 
>>>
>>> btf_log_buf=NULL, btf_size=89, btf_log_size=0, btf_log_level=0}, 120) 
>>> = 5
>>> bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_ARRAY, key_size=4,
>>> value_size=4, max_entries=1, map_flags=0x400 /* BPF_F_??? */,
>>> inner_map_fd=0, map_name="", map_ifindex=0, btf_fd=0, btf_key_type_id=0,
>>> btf_value_type_id=0}, 120) = -1 EPERM (Operation not permitted)
>>> bpf(BPF_BTF_LOAD,
>>> {btf="\237\353\1\0\30\0\0\0\0\0\0\0`\1\0\0`\1\0\0\236\0\0\0\0\0\0\0\0\0\0\3"..., 
>>>
>>> btf_log_buf=NULL, btf_size=534, btf_log_size=0, btf_log_level=0}, 
>>> 120) = 5
>>> bpf(BPF_OBJ_GET_INFO_BY_FD, {info={bpf_fd=3, info_len=208,
>>> info=0x7ffcaedfd4a0}}, 120) = 0
>>> bpf(BPF_OBJ_GET_INFO_BY_FD, {info={bpf_fd=3, info_len=208,
>>> info=0x2018c30}}, 120) = 0
>>> bpf(BPF_BTF_GET_FD_BY_ID, {btf_id=3}, 120) = 4
>>> bpf(BPF_OBJ_GET_INFO_BY_FD, {info={bpf_fd=4, info_len=16,
>>> info=0x7ffcaedfd5a0}}, 120) = 0
>>> libbpf: Cannot find bpf_func_info for main program sec
>>> fexit/xdp_prog_simple. Ignore all bpf_func_info.
>>> bpf(BPF_PROG_LOAD, {prog_type=0x1a /* BPF_PROG_TYPE_??? */, insn_cnt=30,
>>> insns=0x20191f0, license="GPL", log_level=7, log_size=16777215,
>>> log_buf="", kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0,
>>> prog_name="trace_on_exit", prog_ifindex=0, expected_attach_type=0x19 /*
>>> BPF_??? */, prog_btf_fd=5, func_info_rec_size=0, func_info=NULL,
>>> func_info_cnt=0, line_info_rec_size=0, line_info=NULL, line_info_cnt=0,
>>> ...}, 120) = -1 EPERM (Operation not permitted)
>>> libbpf: load bpf program failed: Operation not permitted
>>> libbpf: failed to load program 'fexit/xdp_prog_simple'
>>> libbpf: failed to load object './xdp_sample_fentry_fexit_kern.o'
>>> ERROR: Failed to load object file: Operation not permitted
>>> +++ exited with 0 +++
>>>
>>> And with full libbpf print debugging:
>>>
>>> libbpf: loading ./xdp_sample_fentry_fexit_kern.o
>>> libbpf: section(1) .strtab, size 250, link 0, flags 0, type=3
>>> libbpf: skip section(1) .strtab
>>> libbpf: section(2) .text, size 0, link 0, flags 6, type=1
>>> libbpf: skip section(2) .text
>>> libbpf: section(3) fexit/xdp_prog_simple, size 240, link 0, flags 6, 
>>> type=1
>>> libbpf: found program fexit/xdp_prog_simple
>>> libbpf: section(4) license, size 4, link 0, flags 3, type=1
>>> libbpf: license of ./xdp_sample_fentry_fexit_kern.o is GPL
>>> libbpf: section(5) .rodata.str1.1, size 52, link 0, flags 32, type=1
>>> libbpf: skip section(5) .rodata.str1.1
>>> libbpf: section(6) .debug_str, size 344, link 0, flags 30, type=1
>>> libbpf: skip section(6) .debug_str
>>> libbpf: section(7) .debug_loc, size 70, link 0, flags 0, type=1
>>> libbpf: skip section(7) .debug_loc
>>> libbpf: section(8) .debug_abbrev, size 297, link 0, flags 0, type=1
>>> libbpf: skip section(8) .debug_abbrev
>>> libbpf: section(9) .debug_info, size 403, link 0, flags 0, type=1
>>> libbpf: skip section(9) .debug_info
>>> libbpf: section(10) .rel.debug_info, size 528, link 21, flags 0, type=9
>>> libbpf: skip relo .rel.debug_info(10) for section(9)
>>> libbpf: section(11) .debug_ranges, size 96, link 0, flags 0, type=1
>>> libbpf: skip section(11) .debug_ranges
>>> libbpf: section(12) .debug_macinfo, size 1, link 0, flags 0, type=1
>>> libbpf: skip section(12) .debug_macinfo
>>> libbpf: section(13) .BTF, size 534, link 0, flags 0, type=1
>>> libbpf: section(14) .rel.BTF, size 16, link 21, flags 0, type=9
>>> libbpf: skip relo .rel.BTF(14) for section(13)
>>> libbpf: section(15) .BTF.ext, size 152, link 0, flags 0, type=1
>>> libbpf: section(16) .rel.BTF.ext, size 96, link 21, flags 0, type=9
>>> libbpf: skip relo .rel.BTF.ext(16) for section(15)
>>> libbpf: section(17) .debug_frame, size 40, link 0, flags 0, type=1
>>> libbpf: skip section(17) .debug_frame
>>> libbpf: section(18) .rel.debug_frame, size 32, link 21, flags 0, type=9
>>> libbpf: skip relo .rel.debug_frame(18) for section(17)
>>> libbpf: section(19) .debug_line, size 206, link 0, flags 0, type=1
>>> libbpf: skip section(19) .debug_line
>>> libbpf: section(20) .rel.debug_line, size 16, link 21, flags 0, type=9
>>> libbpf: skip relo .rel.debug_line(20) for section(19)
>>> libbpf: section(21) .symtab, size 792, link 1, flags 0, type=2
>>> libbpf: Cannot find bpf_func_info for main program sec
>>> fexit/xdp_prog_simple. Ignore all bpf_func_info.
>>> libbpf: load bpf program failed: Operation not permitted
>>> libbpf: failed to load program 'fexit/xdp_prog_simple'
>>> libbpf: failed to load object './xdp_sample_fentry_fexit_kern.o'
>>> ERROR: Failed to load object file: Operation not permitted
>>>
>>> I’m using the latest pahole, but standard llvm 9.0.0 from Fedora.
> 
> Same error with latest llvm
> 
>>> So I decided to at least run the self-test and see if this passes, and
>>> work my way from there.
>>> But it’s failing to build with errors like “use of unknown builtin
>>> '__builtin_preserve_field_info’”, so I’m assuming my clang9 needs
>>> upgrading…
>>
>> Yes, please try latest llvm trunk. You can find the information on the
>> web. Below is the instruction from iovisor/bcc repo.
>> (https://github.com/iovisor/bcc/blob/master/INSTALL.md#older-instructions) 
>>
>>
>> git clone https://github.com/llvm/llvm-project.git
>> mkdir -p llvm-project/llvm/build/install
>> cd llvm-project/llvm/build
>> cmake -G "Ninja" -DLLVM_TARGETS_TO_BUILD="BPF;X86" \
>>    -DLLVM_ENABLE_PROJECTS="clang" \
>>    -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=$PWD/install ..
>> ninja && ninja install
>> export PATH=$PWD/install/bin:$PATH
>>
> 
> I tried compiling with the latest master llvm, but the selftest failed 
> for bpf2bpf (other fail to sudo ./test_progs, Summary: 44/138 PASSED, 1 
> SKIPPED, 16 FAILED)
> 
> #5 core_reloc:FAIL
> test_fentry_fexit:PASS:prog_load sched cls 32573 nsec
> libbpf: failed to find valid kernel BTF
> libbpf: vmlinux BTF is not found
> libbpf: fentry/bpf_fentry_test1 is not found in vmlinux BTF
> test_fentry_fexit:FAIL:prog_load fail err -2 errno 2
> #6 fentry_fexit:FAIL
> test_fentry_test:PASS:prog_load sched cls 0 nsec
> libbpf: failed to find valid kernel BTF
> libbpf: vmlinux BTF is not found
> libbpf: fentry/bpf_fentry_test1 is not found in vmlinux BTF
> test_fentry_test:FAIL:prog_load fail err -2 errno 2
> #7 fentry_test:FAIL
> test_fexit_bpf2bpf:PASS:prog_load sched cls 32764 nsec
> test_fexit_bpf2bpf:PASS:obj_open 32764 nsec
> libbpf: failed to find valid kernel BTF
> libbpf: failed to get target BTF: -3
> libbpf: failed to perform CO-RE relocations: -3
> libbpf: failed to load object './fexit_bpf2bpf.o'
> test_fexit_bpf2bpf:FAIL:obj_load err -3
> #8 fexit_bpf2bpf:FAIL
> 
> Is there more I need to re-compile other than the test directory?
> Or do I need additional configure flags?
> 
> $ grep -E -i "btf|bpf" .config
> CONFIG_CGROUP_BPF=y
> CONFIG_BPF=y
> CONFIG_BPF_SYSCALL=y
> CONFIG_BPF_JIT_ALWAYS_ON=y
> CONFIG_IPV6_SEG6_BPF=y
> CONFIG_NETFILTER_XT_MATCH_BPF=m
> # CONFIG_BPFILTER is not set
> CONFIG_NET_CLS_BPF=m
> CONFIG_NET_ACT_BPF=m
> CONFIG_BPF_JIT=y
> CONFIG_BPF_STREAM_PARSER=y
> CONFIG_LWTUNNEL_BPF=y
> CONFIG_HAVE_EBPF_JIT=y
> CONFIG_BPF_LIRC_MODE2=y
> CONFIG_VIDEO_SONY_BTF_MPX=m
> # CONFIG_DEBUG_INFO_BTF is not set

You need to build the kernel with
   CONFIG_DEBUG_INFO_BTF=y
Make sure on the build machine you have recent pahole version >= 1.13.


> CONFIG_BPF_EVENTS=y
> # CONFIG_BPF_KPROBE_OVERRIDE is not set
> # CONFIG_TEST_BPF is not set
> 
> Cheers,
> 
> Eelco
> 
>