init

    pub fn init(ranges_value: *const FormValue, di: *const Dwarf, endian: Endian, compile_unit: *const CompileUnit) !@This() {
        const section_type = if (compile_unit.version >= 5) Section.Id.debug_rnglists else Section.Id.debug_ranges;
        const debug_ranges = di.section(section_type) orelse return error.MissingDebugInfo;

        const ranges_offset = switch (ranges_value.*) {
            .sec_offset, .udata => |off| off,
            .rnglistx => |idx| off: {
                switch (compile_unit.format) {
                    .@"32" => {
                        const offset_loc = compile_unit.rnglists_base + 4 * idx;
                        if (offset_loc + 4 > debug_ranges.len) return bad();
                        const offset = mem.readInt(u32, debug_ranges[@intCast(offset_loc)..][0..4], endian);
                        break :off compile_unit.rnglists_base + offset;
                    },
                    .@"64" => {
                        const offset_loc = compile_unit.rnglists_base + 8 * idx;
                        if (offset_loc + 8 > debug_ranges.len) return bad();
                        const offset = mem.readInt(u64, debug_ranges[@intCast(offset_loc)..][0..8], endian);
                        break :off compile_unit.rnglists_base + offset;
                    },
                }
            },
            else => return bad(),
        };

        // All the addresses in the list are relative to the value
        // specified by DW_AT.low_pc or to some other value encoded
        // in the list itself.
        // If no starting value is specified use zero.
        const base_address = compile_unit.die.getAttrAddr(di, endian, AT.low_pc, compile_unit) catch |err| switch (err) {
            error.MissingDebugInfo => 0,
            else => return err,
        };

        var fr: Reader = .fixed(debug_ranges);
        fr.seek = cast(usize, ranges_offset) orelse return bad();

        return .{
            .base_address = base_address,
            .section_type = section_type,
            .di = di,
            .endian = endian,
            .compile_unit = compile_unit,
            .fr = fr,
        };
    }