Re: [PATCH bpf-next v3 20/20] selftests/bpf: Load an exception cleanup program from a light skeleton

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

On 9/19/26 11:31 PM, bot+bpf-ci@kernel.org wrote:
>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>> index 7ea5ba1df29e..981cc2643049 100644
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -523,7 +523,7 @@ 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
>> +	test_ringbuf_overwrite.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..de7ae478d67f
>> --- /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_preempt_disable();
>> +	bpf_preempt_enable();
>> +	bpf_unwind_resume();
>> +}
> Are the kfunc declarations in scope here? The file includes only
> <vmlinux.h>, <bpf/bpf_helpers.h>, "bpf_misc.h", and
> "exceptions_cleanup.h".
>
> bpf_throw(), bpf_preempt_disable(), and bpf_preempt_enable() are
> normally declared with __ksym in tools/testing/selftests/bpf/
> bpf_experimental.h, which is not included. bpf_unwind_resume() has no
> declaration in any userspace header in the tree.

I prefer to use vmlinux.h.

>
> Without __ksym == __attribute__((section(".ksyms"))), these become
> implicit function declarations, and libbpf's bpf_object__collect_externs()
> will reject any extern not in a ".ksyms" DATASEC when it tries to
> relocate the calls in the inline asm below.
>
> The __kfunc_btf_anchor() function exists specifically to produce extern
> BTF FUNCs that libbpf can relocate for the 'call bpf_throw' and
> 'call bpf_unwind_resume' sites in the inline asm. If the declarations
> are implicit, either the compile fails or bpftool rejects the object when
> generating the light skeleton.
>
> Should this file include "bpf_experimental.h" and add a declaration for
> bpf_unwind_resume()? The identical pattern appears in
> progs/exceptions_cleanup.c, progs/exceptions_cleanup_shapes.c, and
> progs/exceptions_cleanup_ext_table.c from earlier commits in this series,
> so the fix may need to be series-wide.
>
>> +
>> +__u64 pads_ran = 0;
>> +
>> +SEC("syscall")
>> +__naked int entry_light(void)
>> +{
>> +	asm volatile (
>> +	"call bpf_preempt_disable;"
>> +	"r1 = %[cookie];"
>> +"1:"	"call bpf_throw;"		/* cleanup region */
>> +"2:"
>> +	"exit;"
>> +"3:"					/* landing pad */
>> +	"call bpf_preempt_enable;"
>> +	PAD_RAN("%[ran]")
>> +	"call bpf_unwind_resume;"
>> +	"exit;"
>> +	CLEANUP_REC("1b", "2b", "3b")
>> +	:
>> +	: [cookie]"i"(THROW_COOKIE), [ran]"i"(RAN_LIGHT),
>> +	  __imm_addr(pads_ran)
>> +	: __clobber_all);
>> +}
>> +
>> +char _license[] SEC("license") = "GPL";
>
> ---
> 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/35492765538