linux-kernel - Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch

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Message-ID: <YTHcki5RLZIIGqbk@hirez.programming.kicks-ass.net>
Date:   Fri, 3 Sep 2021 10:28:02 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
        mingo@...hat.com, kjain@...ux.ibm.com, kernel-team@...com
Subject: Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper
 bpf_get_branch_snapshot

On Thu, Sep 02, 2021 at 09:57:05AM -0700, Song Liu wrote:
> +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;
> +
> +	if (unlikely(flags))
> +		return -EINVAL;
> +
> +	if (!buf || (size % br_entry_size != 0))
> +		return -EINVAL;
> +
> +	entry_cnt = static_call(perf_snapshot_branch_stack)(buf, entry_cnt);
> +
> +	if (!entry_cnt)
> +		return -ENOENT;
> +
> +	return entry_cnt * br_entry_size;
> +#endif
> +}

Do we really need that CONFIG_X86 thing? Seems rather bad practise.