Re: [PATCH v2] selftests/bpf: avoid jump seq limit in verif_scale_pyperf600

[Paul Chaignon <paul.chaignon@gmail.com>]

On Fri, Mar 06, 2026 at 08:00:24PM +0800, Sun Jian wrote:
> pyperf600 is a verifier scale test. With newer LLVM, calling __on_event()
> twice can push the generated program over the verifier jump sequence
> complexity limit (8192), failing with:
> 
>   The sequence of 8193 jumps is too complex.
> 
> Let pyperf600 provide its own on_event() that calls __on_event() once, and
> guard the shared wrapper accordingly. Other pyperf600 variants are
> unaffected.
> 
> Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
> ---
> 
> v2:
>   - Drop runtime -E2BIG skip; instead tweak pyperf600 program source to avoid
>     hitting the verifier jump sequence complexity limit.
>   - verif_scale_pyperf600 now passes; other pyperf600 variants unchanged.
> 
>  tools/testing/selftests/bpf/progs/pyperf.h    | 4 +++-
>  tools/testing/selftests/bpf/progs/pyperf600.c | 7 +++++++
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/progs/pyperf.h b/tools/testing/selftests/bpf/progs/pyperf.h
> index 86484f07e1d1..c02c49c52c77 100644
> --- a/tools/testing/selftests/bpf/progs/pyperf.h
> +++ b/tools/testing/selftests/bpf/progs/pyperf.h
> @@ -343,8 +343,9 @@ int __on_event(struct bpf_raw_tracepoint_args *ctx)
>  	return 0;
>  }
>  
> +#ifndef PYPERF_CUSTOM_ON_EVENT
>  SEC("raw_tracepoint/kfree_skb")
> -int on_event(struct bpf_raw_tracepoint_args* ctx)
> +int on_event(struct bpf_raw_tracepoint_args *ctx)
>  {
>  	int ret = 0;
>  	ret |= __on_event(ctx);
> @@ -354,5 +355,6 @@ int on_event(struct bpf_raw_tracepoint_args* ctx)
>  	ret |= __on_event(ctx);
>  	return ret;
>  }
> +#endif
>  
>  char _license[] SEC("license") = "GPL";
> diff --git a/tools/testing/selftests/bpf/progs/pyperf600.c b/tools/testing/selftests/bpf/progs/pyperf600.c
> index ce1aa5189cc4..31e8a422d804 100644
> --- a/tools/testing/selftests/bpf/progs/pyperf600.c
> +++ b/tools/testing/selftests/bpf/progs/pyperf600.c
> @@ -9,4 +9,11 @@
>   * the loop will still execute 600 times.
>   */
>  #define UNROLL_COUNT 150
> +#define PYPERF_CUSTOM_ON_EVENT
>  #include "pyperf.h"
> +
> +SEC("raw_tracepoint/kfree_skb")
> +int on_event(struct bpf_raw_tracepoint_args *ctx)
> +{
> +	return __on_event(ctx);
> +}

I'm not sure I like this approach. It feels like the 600 in pyperf600
wouldn't really be comparable to the 600 or the 180 in other test cases
since they wouldn't correspond to the same program (yours in five times
shorter). A low-effort alternative would be to tweak STACK_MAX_LEN and
UNROLL_COUNT, but I only managed to make that work by reducing
STACK_MAX_LEN to 180 and then I guess there isn't much difference with
pyperf180 :(

Ideally we would understand what changes in the bytecode with LLVM 19+
and mitigate that by adapting __on_event.

> 
> base-commit: 5ee8dbf54602dc340d6235b1d6aa17c0f283f48c
> -- 
> 2.43.0
> 
>