Hello,
I'm having a problem of loading perf lock contention BPF program [1]
on old kernels. It has collect_lock_syms() to get the address of each
CPU's run-queue lock. The kernel 5.14 changed the name of the field
so there's bpf_core_field_exists to check the name like below.
if (bpf_core_field_exists(rq_new->__lock))
lock_addr = (__u64)&rq_new->__lock;
else
lock_addr = (__u64)&rq_old->lock;
Note that I've applied a patch [2] to fix an issue with this code.
It works fine on my machine (with a newer kernel), but failed on the
old kernels. I guess it'd go to the else part without a problem but
it didn't for some reason.
Then I change the code to check the rq_old first. It works well on
the old kernels but fails on newer kernels.. :(
libbpf: prog 'collect_lock_syms': BPF program load failed: Invalid argument
libbpf: prog 'collect_lock_syms': -- BEGIN PROG LOAD LOG --
reg type unsupported for arg#0 function collect_lock_syms#380
0: R1=ctx(off=0,imm=0) R10=fp0
; int BPF_PROG(collect_lock_syms)
0: (b7) r6 = 0 ; R6_w=0
1: (b7) r7 = 0 ; R7_w=0
2: (b7) r9 = 1 ; R9_w=1
3: <invalid CO-RE relocation>
failed to resolve CO-RE relocation <byte_off> [381] struct rq___old.lock (0:0 @ offset 0)
processed 4 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
I'm curious what went wrong with this. I guess it's supposed to work
on any kernel verions by definition. Not sure the compiler generated
a wrong reloc or something. Maybe I just made silly mistakes..
Do you see anything wrong? Any hints to debug this issue?
Thanks,
Namhyung
[1] file://linux/tools/perf/util/bpf_skel/lock_contention.bpf.c
[2] https://lore.kernel.org/lkml/20230423215650.287812-1-namhyung@xxxxxxxxxx/
