Re: [PATCH v2 01/13] bpf: Add bpf_stream_print_stack stack dumping kfunc

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 1/27/26 18:15, Emil Tsalapatis wrote:
> From: Emil Tsalapatis <etsal@meta.com>
>
> Add a new kfunc called bpf_stream_print_stack to be used by programs
> that need to print out their current BPF stack. The kfunc is essentially
> a wrapper around the existing bpf_stream_dump_stack functionality used
> to generate stack traces for error events like may_goto violations and
> BPF-side arena page faults.
>
> Signed-off-by: Emil Tsalapatis (Meta) <emil@etsalapatis.com>
> ---
>   kernel/bpf/helpers.c        |  1 +
>   kernel/bpf/stream.c         | 13 +++++++++++++
>   tools/lib/bpf/bpf_helpers.h |  2 ++
>   3 files changed, 16 insertions(+)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index b54ec0e945aa..c30a9f68af6b 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -4562,6 +4562,7 @@ BTF_ID_FLAGS(func, bpf_strncasestr);
>   BTF_ID_FLAGS(func, bpf_cgroup_read_xattr, KF_RCU)
>   #endif
>   BTF_ID_FLAGS(func, bpf_stream_vprintk, KF_IMPLICIT_ARGS)
> +BTF_ID_FLAGS(func, bpf_stream_print_stack, KF_IMPLICIT_ARGS)
>   BTF_ID_FLAGS(func, bpf_task_work_schedule_signal, KF_IMPLICIT_ARGS)
>   BTF_ID_FLAGS(func, bpf_task_work_schedule_resume, KF_IMPLICIT_ARGS)
>   BTF_ID_FLAGS(func, bpf_dynptr_from_file)
> diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
> index 24730df55e69..6e2cbe5f34e7 100644
> --- a/kernel/bpf/stream.c
> +++ b/kernel/bpf/stream.c
> @@ -245,6 +245,19 @@ __bpf_kfunc int bpf_stream_vprintk(int stream_id, const char *fmt__str, const vo
>   	return ret;
>   }
>   
> +/* Directly trigger a stack dump from the program. */
> +__bpf_kfunc void bpf_stream_print_stack(struct bpf_prog_aux *aux)
> +{
> +	struct bpf_stream_stage ss;
> +	struct bpf_prog *prog;
> +
> +	prog = aux->main_prog_aux->prog;
> +
> +	bpf_stream_stage(ss, prog, BPF_STDERR, ({
> +		bpf_stream_dump_stack(ss);
> +	}));
> +}
> +
>   __bpf_kfunc_end_defs();
>   
>   /* Added kfunc to common_btf_ids */
> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> index c145da05a67c..6d8ae3887618 100644
> --- a/tools/lib/bpf/bpf_helpers.h
> +++ b/tools/lib/bpf/bpf_helpers.h
> @@ -343,6 +343,8 @@ extern int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *a
>   /* Helper macro to print out debug messages */
>   #define bpf_printk(fmt, args...) ___bpf_pick_printk(args)(fmt, ##args)
>   
> +extern void bpf_stream_print_stack(void) __weak __ksym;
> +
Is this needed? bpf_stream_print_stack() should be available via 
vmlinux.h, shouldn't it?
>   struct bpf_iter_num;
>   
>   extern int bpf_iter_num_new(struct bpf_iter_num *it, int start, int end) __weak __ksym;