Re: [PATCH bpf-next v2 18/20] selftests/bpf: Add an end-to-end .bpf_cleanup exception test

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

On 9/17/26 10:58 PM, bot+bpf-ci@kernel.org wrote:
>> diff --git a/tools/testing/selftests/bpf/progs/exceptions_cleanup_fail.c b/tools/testing/selftests/bpf/progs/exceptions_cleanup_fail.c
>> new file mode 100644
>> index 0000000000000..ce2dac306a84c
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/exceptions_cleanup_fail.c
>> @@ -0,0 +1,600 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
>> +#include <vmlinux.h>
>> +#include <bpf/bpf_helpers.h>
>> +#include "bpf_experimental.h"
>> +#include "bpf_misc.h"
>> +#include "../test_kmods/bpf_testmod_kfunc.h"
>> +#include "exceptions_cleanup.h"
>> +
>> +__u64 input = 0;
>> +
>> +static __used __noinline void __kfunc_btf_anchor(void)
>> +{
>> +	bpf_throw(0);
>> +	bpf_preempt_disable();
>> +	bpf_preempt_enable();
>> +	bpf_unwind_resume();
>> +}
> Is bpf_unwind_resume() declared anywhere?  It is called from C here but
> bpf_experimental.h declares only the other kfuncs this anchor exists for:
>
> tools/testing/selftests/bpf/bpf_experimental.h declares bpf_throw():
>
>      extern void bpf_throw(u64 cookie) __ksym;
>
> and the preempt pair:
>
>      void bpf_preempt_disable(void) __weak __ksym;
>      void bpf_preempt_enable(void) __weak __ksym;
>
> but bpf_unwind_resume() does not appear in any header. vmlinux.h contains
> type definitions only, not kfunc prototypes.
>
> BPF objects are built with BPF_CFLAGS = -g -Wall -Werror -std=gnu11
> (tools/testing/selftests/bpf/Makefile). -Wimplicit-function-declaration
> is part of -Wall, and in C99+ mode modern Clang promotes it to an error,
> which with -Werror becomes fatal:
>
>    progs/exceptions_cleanup_fail.c:17:2: error: call to undeclared
>      function 'bpf_unwind_resume'; ISO C99 and later do not support
>      implicit function declarations
>
> This would break the build of the whole BPF selftests tree. The same C-level
> call appears in the three other new prog files added by this series
> (progs/exceptions_cleanup.c, and in follow-ups progs/exceptions_cleanup_shapes.c
> and progs/exceptions_cleanup_light.c), so all of them would fail to compile.
>
> The anchor cannot simply drop the call either: the C call is what makes Clang
> emit the BTF extern FUNC for bpf_unwind_resume, which libbpf needs to resolve
> the inline-asm "call bpf_unwind_resume;" relocations. The fix would be to add
> the declaration:
>
>      extern void bpf_unwind_resume(void) __ksym;
>
> in bpf_experimental.h alongside bpf_throw(). For comparison,
> progs/exceptions_cleanup_shapes.c (commit 198e7e8d6d72) does declare its
> sibling explicitly:
>
>      extern void _Unwind_Resume(void) __ksym;

I didn't find anything wrong with this patch set and with my normal environment,
the test works fine.

>
> ---
> 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/35308528711