// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build linux && arm64
// +build linux,arm64

package cpu

import (
	"errors"
	"io"
	"os"
	"strings"
)

func readLinuxProcCPUInfo() error {
	f, err := os.Open("/proc/cpuinfo")
	if err != nil {
		return err
	}
	defer f.Close()

	var buf [1 << 10]byte // enough for first CPU
	n, err := io.ReadFull(f, buf[:])
	if err != nil && err != io.ErrUnexpectedEOF {
		return err
	}
	in := string(buf[:n])
	const features = "\nFeatures	: "
	i := strings.Index(in, features)
	if i == -1 {
		return errors.New("no CPU features found")
	}
	in = in[i+len(features):]
	if i := strings.Index(in, "\n"); i != -1 {
		in = in[:i]
	}
	m := map[string]*bool{}

	initOptions() // need it early here; it's harmless to call twice
	for _, o := range options {
		m[o.Name] = o.Feature
	}
	// The EVTSTRM field has alias "evstrm" in Go, but Linux calls it "evtstrm".
	m["evtstrm"] = &ARM64.HasEVTSTRM

	for _, f := range strings.Fields(in) {
		if p, ok := m[f]; ok {
			*p = true
		}
	}
	return nil
}