Re: [PATCH bpf v4 05/11] selftests/bpf: Test early in-kernel CO-RE relocation

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Wed Sep 16, 2026 at 8:23 PM CEST, Eduard Zingerman wrote:
> On Tue, 2026-09-15 at 00:25 +0200, Kumar Kartikeya Dwivedi wrote:
>> Add a raw program load with CO-RE relocation metadata but no func_info or
>> line_info. Place the relocation in dead code and require the poisoning log,
>> proving that the kernel processes standalone CO-RE metadata instead of
>> silently skipping it.
>>
>> Also poison a subprogram's terminal exit and require check_subprogs() to
>> reject the resulting fall-through. This confirms that in-kernel CO-RE runs
>> before the verifier validates the subprogram layout and before later CFG
>> consumers rely on it.
>>
>> Load both instruction streams without relocation metadata first to ensure
>> that CO-RE processing causes the rejection and diagnostic.
>>
>> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
>> ---
>
> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
>
>> +static void test_early_core_relo(void)
>> +{
>> +	struct bpf_insn core_only[] = {
>> +		BPF_MOV64_IMM(BPF_REG_0, 0),
>> +		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
>> +		BPF_MOV64_IMM(BPF_REG_0, 0),
>> +		BPF_EXIT_INSN(),
>> +	};
>> +	struct bpf_insn subprog[] = {
>> +		BPF_CALL_REL(2),
>> +		BPF_MOV64_IMM(BPF_REG_0, 0),
>> +		BPF_EXIT_INSN(),
>> +		BPF_MOV64_IMM(BPF_REG_0, 0),
>> +		BPF_EXIT_INSN(),
>> +	};
>> +	struct bpf_func_info funcs[2];
>> +	const void *raw_btf;
>> +	struct btf *btf;
>> +	__u32 raw_btf_size;
>> +	int access_str_off, btf_fd = -1, enum_id;
>> +	int int_id, main_id, prog_fd = -1, proto_id, sub_id;
>> +
>> +	btf = btf__new_empty();
>> +	if (!ASSERT_OK_PTR(btf, "btf_new_empty"))
>> +		return;
>> +	int_id = btf__add_int(btf, "int", 4, BTF_INT_SIGNED);
>> +	if (!ASSERT_GT(int_id, 0, "add_int"))
>> +		goto cleanup;
>> +	proto_id = btf__add_func_proto(btf, int_id);
>> +	if (!ASSERT_GT(proto_id, 0, "add_func_proto"))
>> +		goto cleanup;
>> +	main_id = btf__add_func(btf, "main_fn", BTF_FUNC_STATIC, proto_id);
>> +	if (!ASSERT_GT(main_id, 0, "add_main_func"))
>> +		goto cleanup;
>> +	sub_id = btf__add_func(btf, "sub_fn", BTF_FUNC_STATIC, proto_id);
>> +	if (!ASSERT_GT(sub_id, 0, "add_sub_func"))
>> +		goto cleanup;
>> +	enum_id = btf__add_enum(btf, "core_relo_poison_missing", 4);
>> +	if (!ASSERT_GT(enum_id, 0, "add_enum") ||
>> +	    !ASSERT_OK(btf__add_enum_value(btf, "value", 0), "add_enum_value"))
>> +		goto cleanup;
>> +	access_str_off = btf__add_str(btf, "0");
>> +	if (!ASSERT_GT(access_str_off, 0, "add_access_str"))
>> +		goto cleanup;
>
> I asked to update this to use utility macro, but if there are no other
> nits let's land as-is.
>
> ...

I have a local follow up, will send once this lands.
Thanks