Re: [PATCH bpf-next v4 12/13] selftests/bpf: Add tests for callbacks returning more than 8 bytes

[Yonghong Song <yonghong.song@linux.dev>]

On 8/12/26 5:10 PM, Eduard Zingerman wrote:
> On Mon, 2026-08-10 at 17:10 -0700, Yonghong Song wrote:
>> Add two __failure tests covering the callback return-size checks:
>>
>>   - timer_ret_pair_fail: a bpf_timer callback declared to return more than
>>     8 bytes, rejected by check_ld_imm() where the callback's PTR_TO_FUNC is
>>     created, with "callback function with >8-byte return value is not
>>     supported".
>>
>>   - exceptions_ret_pair_fail: an exception callback declared to return more
>>     than 8 bytes, rejected by do_check_common() when the callback
>>     subprogram is verified, with "exception cb cannot return value larger
>>     than 8 bytes".
>>
>> Both callback bodies are written in inline asm so that the tests do not
>> depend on LLVM 23 R0:R2 codegen and run on any compiler. The verifier reads
>> the return type from BTF rather than from the instructions, so the >8 byte
>> return prototype is supplied through __btf_func_path(), pointing at a
>> companion btf__*.c program that exists only to carry that BTF.
>>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
>> ---
>>   .../selftests/bpf/prog_tests/exceptions.c     |  2 +
>>   .../testing/selftests/bpf/prog_tests/timer.c  |  2 +
>>   .../bpf/progs/btf__exceptions_ret_pair_fail.c | 10 ++++
>>   .../bpf/progs/btf__timer_ret_pair_fail.c      | 10 ++++
>>   .../bpf/progs/exceptions_ret_pair_fail.c      | 30 ++++++++++++
>>   .../selftests/bpf/progs/timer_ret_pair_fail.c | 49 +++++++++++++++++++
>>   6 files changed, 103 insertions(+)
> Dropping callback checks avoids adding all this code.

Yes, I removed 'bpf: Reject callbacks returning more than 8 bytes' so
this patch will be removed as well.

>
> ...