xdpdump fails when XDP function BPF-prog names are too long about xdp-tools

[netoptimizer]

Issues with xdpdump can be debugged via supplying -vv for more verbose.
I provided full output in pastebin here: https://pastebin.com/KzSCvMqM

Important line is:

libbpf: xdp_tailgrow_fu is not found in prog's BTF

[tohojo]

**Help/hints to solve:** I think the xdpdump program can find the associated full-length name via BTF info. The ```struct bpf_prog_aux``` have a (```const char *```) member named ```attach_func_name```, that I think we can extract somehow (according to comment this is "function name for valid attach_btf_id").

We don't even need to look at bpf_prog_aux - just get the BTF from the program from the kernel and iterate that. Functions are stored directly in the BTF info, e.g. as [7] here: $ bpftool btf dump file xdp_pass_kern.o [1] PTR '(anon)' type_id=2 [2] STRUCT 'xdp_md' size=20 vlen=5 'data' type_id=3 bits_offset=0 'data_end' type_id=3 bits_offset=32 'data_meta' type_id=3 bits_offset=64 'ingress_ifindex' type_id=3 bits_offset=96 'rx_queue_index' type_id=3 bits_offset=128 [3] TYPEDEF '__u32' type_id=4 [4] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none) [5] FUNC_PROTO '(anon)' ret_type_id=6 vlen=1 'ctx' type_id=1 [6] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED [7] FUNC 'xdp_prog_simple' type_id=5 linkage=global [8] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED [9] ARRAY '(anon)' type_id=8 index_type_id=10 nr_elems=4 [10] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding [11] VAR '_license' type_id=9, linkage=global-alloc [12] DATASEC 'license' size=0 vlen=1 type_id=11 offset=0 size=4 There's already some code in libxdp.c that iterates the BTF info - see btf_get_datasec()

[chaudron]

Not sure how to extract attach_func_name from userspace, as this would be the best option. @netoptimizer any idea without a kernel change?

@tohojo's idea of using the btf might work, but not if there are two long functions with the same 16 chars. For example:

# bpftool btf dump id 1072 | grep xdp_test_prog_w
[7] FUNC 'xdp_test_prog_with_a_long_name' type_id=5
[9] FUNC 'xdp_test_prog_with_a_long_name_too' type_id=8

Guess I can still use the BTF info, and drop an error when two long functions with the same name exits.

This will then be solved when I add multiple program support, as there you can enter the full name of the function(s) you would like to trace.