Re: [PATCH bpf-next v7 22/22] selftests/bpf: Load an exception cleanup program from a light skeleton

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

On 9/28/26 5:52 PM, bot+bpf-ci@kernel.org wrote:
>> diff --git a/tools/testing/selftests/bpf/Makefile.skel b/tools/testing/selftests/bpf/Makefile.skel
>> index 2e22bb901bf3..41575e180efb 100644
>> --- a/tools/testing/selftests/bpf/Makefile.skel
>> +++ b/tools/testing/selftests/bpf/Makefile.skel
>> @@ -33,7 +33,7 @@ LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h		\
>>   LSKELS := fexit_sleep.c trace_printk.c trace_vprintk.c map_ptr_kern.c 	\
>>   	core_kern.c core_kern_overflow.c test_ringbuf.c			\
>>   	test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c    \
>> -	test_ringbuf_overwrite.c callx_rodata.c
>> +	test_ringbuf_overwrite.c callx_rodata.c exceptions_cleanup_light.c
> [ ... ]
>
>> diff --git a/tools/testing/selftests/bpf/progs/exceptions_cleanup_light.c b/tools/testing/selftests/bpf/progs/exceptions_cleanup_light.c
>> new file mode 100644
>> index 000000000000..19d53569bbda
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/exceptions_cleanup_light.c
>> @@ -0,0 +1,39 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
>> +#include <vmlinux.h>
>> +#include <bpf/bpf_helpers.h>
>> +#include "bpf_misc.h"
>> +#include "exceptions_cleanup.h"
>> +
>> +static __used __noinline void __kfunc_btf_anchor(void)
>> +{
>> +	bpf_throw(0);
>> +	bpf_unwind();
>> +	bpf_preempt_disable();
>> +	bpf_preempt_enable();
>> +	bpf_unwind_resume(NULL);
>> +}
>> +
>> +__u64 pads_ran = 0;
>> +
>> +SEC("syscall")
>> +__naked int entry_light(void)
>> +{
>> +	asm volatile (
>> +	"call bpf_preempt_disable;"
>> +"1:"	"call bpf_unwind;"		/* cleanup region */
>> +"2:"
>> +	"exit;"
>> +"3:"					/* landing pad */
>> +	"call bpf_preempt_enable;"
>> +	PAD_RAN("%[ran]")
>> +	"call bpf_unwind_resume;"
>> +	"exit;"
>> +	CLEANUP_REC("1b", "2b", "3b")
>> +	:
>> +	: [ran]"i"(RAN_LIGHT),
>> +	  __imm_addr(pads_ran)
>> +	: __clobber_all);
>> +}
>> +
>> +char _license[] SEC("license") = "GPL";
> A subsystem pattern flags this as potentially concerning:
>
> This adds a new BPF program file to test loading a cleanup table through
> the light skeleton path. The commit message states this is the smallest
> program that can verify whether the table survives the trip through
> bpf_gen__prog_load().
>
> However, progs/exceptions_cleanup.c already covers the same behavior
> more broadly - pads run on unwind and set bits in pads_ran. Makefile.skel
> already has LSKELS_EXTRA for building programs as both light skeleton
> and libbpf skeleton. Could exceptions_cleanup.c be built as a light
> skeleton and have the existing test cases (no_unwind, unwind_from_foo3,
> unwind_from_foo2) run through the gen loader path?
>
> That approach would also exercise the light skeleton code paths this new
> program never reaches. The new program has only one record in the main
> function, so in bpf_prog_collect_cleanup_info() it takes the owner == prog
> branch. The owner->sub_insn_off rebasing for records inside appended
> subprograms, and the multi-frame bpf_unwind_rewrite() walk, would not run
> under the gen loader with this minimal test.
>
> Should this be a light-skeleton case of the existing exceptions_cleanup.c
> instead of a separate file?

Okay, will follow your suggestions.

>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/36502848904