// It saves the address ranges of the mappings in b.mem for use
// when emitting locations.
func (b *profileBuilder) readMapping() {
	data, _ := os.ReadFile("/proc/self/maps")
	parseProcSelfMaps(data, b.addMapping)
	if len(b.mem) == 0 { // pprof expects a map entry, so fake one.
		b.addMappingEntry(0, 0, 0, "", "", true)
		// TODO(hyangah): make addMapping return *memMap or

		// Figure out two addresses from /proc/self/maps.
		mmap, err := os.ReadFile("/proc/self/maps")
		if err != nil {
			t.Fatal(err)
		}
		var mappings []*profile.Mapping
		id := uint64(1)
		parseProcSelfMaps(mmap, func(lo, hi, offset uint64, file, buildID string) {
			mappings = append(mappings, &profile.Mapping{
				ID:      id,
				Start:   lo,
				Limit:   hi,
				Offset:  offset,
				File:    file,

		b.pb.int64Opt(tagFunction_StartLine, fn.startLine)
		b.pb.endMessage(tagProfile_Function, start)
	}

	b.flush()
	return id
}

var space = []byte(" ")
var newline = []byte("\n")

func parseProcSelfMaps(data []byte, addMapping func(lo, hi, offset uint64, file, buildID string)) {
	// $ cat /proc/self/maps
	// 00400000-0040b000 r-xp 00000000 fc:01 787766                             /bin/cat