Re: [PATCH bpf-next 1/3] bpf: make bpf_get_branch_snapshot() architecture-agnostic

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Mar 21, 2024 at 11:04:59AM -0700, Andrii Nakryiko wrote:
> perf_snapshot_branch_stack is set up in an architecture-agnostic way, so
> there is no reason for BPF subsystem to keep track of which
> architectures do support LBR or not. E.g., it looks like ARM64 might soon
> get support for BRBE ([0]), which (with proper integration) should be
> possible to utilize using this BPF helper.
> 
> perf_snapshot_branch_stack static call will point to
> __static_call_return0() by default, which just returns zero, which will
> lead to -ENOENT, as expected. So no need to guard anything here.
> 
>   [0] https://lore.kernel.org/linux-arm-kernel/20240125094119.2542332-1-anshuman.khandual@arm.com/
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  kernel/trace/bpf_trace.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 434e3ece6688..6d000332b17b 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1182,9 +1182,6 @@ static const struct bpf_func_proto bpf_get_attach_cookie_proto_tracing = {
>  
>  BPF_CALL_3(bpf_get_branch_snapshot, void *, buf, u32, size, u64, flags)
>  {
> -#ifndef CONFIG_X86
> -	return -ENOENT;
> -#else
>  	static const u32 br_entry_size = sizeof(struct perf_branch_entry);
>  	u32 entry_cnt = size / br_entry_size;
>  
> @@ -1197,7 +1194,6 @@ BPF_CALL_3(bpf_get_branch_snapshot, void *, buf, u32, size, u64, flags)
>  		return -ENOENT;
>  
>  	return entry_cnt * br_entry_size;
> -#endif
>  }
>  
>  static const struct bpf_func_proto bpf_get_branch_snapshot_proto = {
> -- 
> 2.43.0
> 
>