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.