Jesper Dangaard Brouer 0542d8a7a3 ktrace-CO-RE/ktrace01: Add --debug option to userspace loader ...

Use this --debug to better understand what libbpf does of
CO-RE relocation tricks and lookup of BTF-IDs.

Example output:

 [...]
 libbpf: loading kernel BTF '/sys/kernel/btf/vmlinux': 0
 libbpf: map 'ktrace01.data': created successfully, fd=4
 libbpf: sec 'kprobe/udp_send_skb': found 4 CO-RE relocations
 libbpf: prog 'udp_send_skb': relo #0: kind <byte_off> (0), spec is [2] struct pt_regs.di (0:14 @ offset 112)
 libbpf: CO-RE relocating [0] struct pt_regs: found target candidate [176] struct pt_regs in [vmlinux]
 libbpf: prog 'udp_send_skb': relo #0: matching candidate #0 [176] struct pt_regs.di (0:14 @ offset 112)
 libbpf: prog 'udp_send_skb': relo #0: patched insn #0 (LDX/ST/STX) off 112 -> 112
 libbpf: prog 'udp_send_skb': relo #1: kind <byte_off> (0), spec is [7] struct sk_buff___local.hash (0:1 @ offset 4)
 libbpf: CO-RE relocating [0] struct sk_buff___local: found target candidate [2965] struct sk_buff in [vmlinux]
 [...]

Notice how the BTF-ID of 'struct sk_buff' is resolved to be 2965.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

2021-06-24 17:55:58 +02:00

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