// 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