perf test 40 Basic BPF llvm compile dumps core (x86 and s390)

[Thomas Richter <tmricht@linux.ibm.com>]

I noticed perf test 40.1 dumps core on 5.13.0rc2 and rc3:

[root@f34 perf]# ./perf test -F 40
40: LLVM search and compile                                         :
40.1: Basic BPF llvm compile                                        :
libbpf: elf: skipping unrecognized data section(8) .eh_frame
libbpf: elf: skipping relo section(9) .rel.eh_frame for section(8) .eh_frame
Segmentation fault (core dumped)
[root@f34 perf]#

The root cause is a NULL pointer reference in function btf__get_nr_types()
as can be seen with gdb:

Breakpoint 1, 0x000000000065f4b1 in btf__get_nr_types
     (btf=btf@entry=0x0) at btf.c:425
425		return btf->start_id + btf->nr_types - 1;

This is the same function and reason why test case 42.1 Basic BPF filtering
fails and dumps core too.

The call chain is:
(gdb) where
 #0  0x000000000065f4b1 in btf__get_nr_types (btf=btf@entry=0x0) at btf.c:425
 #1  btf__find_by_name_kind (btf=btf@entry=0x0,
		type_name=type_name@entry=0x928ab2 ".ksyms",
		kind=kind@entry=15) at btf.c:696
 #2  0x00000000006527fe in add_dummy_ksym_var (btf=0x0) at libbpf.c:3219
 #3  bpf_object__collect_externs (obj=0xd0ea20) at libbpf.c:3266
 #4  __bpf_object__open (path=<optimized out>, path@entry=0x0,
		obj_buf=obj_buf@entry=0xd12fa0,
		obj_buf_sz=obj_buf_sz@entry=1520,
    		opts=opts@entry=0x7fffffffdb30) at libbpf.c:7372
 #5  0x0000000000655415 in __bpf_object__open (opts=0x7fffffffdb30,
		obj_buf_sz=1520, obj_buf=0xd12fa0, path=0x0) at libbpf.c:7337
 #6  bpf_object__open_mem (opts=0x7fffffffdb30, obj_buf_sz=1520,
		obj_buf=0xd12fa0) at libbpf.c:7454
 #7  bpf_object__open_mem (opts=0x7fffffffdb30, obj_buf_sz=1520,
		obj_buf=0xd12fa0) at libbpf.c:7448
 #8  bpf_object__open_buffer (obj_buf=0xd12fa0, obj_buf_sz=1520,
		name=<optimized out>) at libbpf.c:7471
 #9  0x00000000004c8c6e in test__bpf_parsing (obj_buf=0xd12fa0,
		obj_buf_sz=1520) at tests/llvm.c:16
 #10 0x00000000004c8fe2 in test__llvm (test=0xac7d20 <generic_tests+2496>,
		subtest=0) at tests/llvm.c:142
...

I have no knowledge about BPF and why the core dump happens. Before
I start digging into this has anybody some hints on where to look?

Thanks a lot.

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
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