parse

pub fn parse(
    cie_bytes: []const u8,
    pc_rel_offset: i64,
    is_runtime: bool,
    format: Format,
    dwarf_section: Section.Id,
    length_offset: u64,
    addr_size_bytes: u8,
    endian: std.builtin.Endian,
) !CommonInformationEntry {
    if (addr_size_bytes > 8) return error.UnsupportedAddrSize;

    var fbr: FixedBufferReader = .{ .buf = cie_bytes, .endian = endian };

    const version = try fbr.readByte();
    switch (dwarf_section) {
        .eh_frame => if (version != 1 and version != 3) return error.UnsupportedDwarfVersion,
        .debug_frame => if (version != 4) return error.UnsupportedDwarfVersion,
        else => return error.UnsupportedDwarfSection,
    }

    var has_eh_data = false;
    var has_aug_data = false;

    var aug_str_len: usize = 0;
    const aug_str_start = fbr.pos;
    var aug_byte = try fbr.readByte();
    while (aug_byte != 0) : (aug_byte = try fbr.readByte()) {
        switch (aug_byte) {
            'z' => {
                if (aug_str_len != 0) return bad();
                has_aug_data = true;
            },
            'e' => {
                if (has_aug_data or aug_str_len != 0) return bad();
                if (try fbr.readByte() != 'h') return bad();
                has_eh_data = true;
            },
            else => if (has_eh_data) return bad(),
        }

        aug_str_len += 1;
    }

    if (has_eh_data) {
        // legacy data created by older versions of gcc - unsupported here
        for (0..addr_size_bytes) |_| _ = try fbr.readByte();
    }

    const address_size = if (version == 4) try fbr.readByte() else addr_size_bytes;
    const segment_selector_size = if (version == 4) try fbr.readByte() else null;

    const code_alignment_factor = try fbr.readUleb128(u32);
    const data_alignment_factor = try fbr.readIleb128(i32);
    const return_address_register = if (version == 1) try fbr.readByte() else try fbr.readUleb128(u8);

    var lsda_pointer_enc: u8 = EH.PE.omit;
    var personality_enc: ?u8 = null;
    var personality_routine_pointer: ?u64 = null;
    var fde_pointer_enc: u8 = EH.PE.absptr;

    var aug_data: []const u8 = &[_]u8{};
    const aug_str = if (has_aug_data) blk: {
        const aug_data_len = try fbr.readUleb128(usize);
        const aug_data_start = fbr.pos;
        aug_data = cie_bytes[aug_data_start..][0..aug_data_len];

        const aug_str = cie_bytes[aug_str_start..][0..aug_str_len];
        for (aug_str[1..]) |byte| {
            switch (byte) {
                'L' => {
                    lsda_pointer_enc = try fbr.readByte();
                },
                'P' => {
                    personality_enc = try fbr.readByte();
                    personality_routine_pointer = try readEhPointer(&fbr, personality_enc.?, addr_size_bytes, .{
                        .pc_rel_base = try pcRelBase(@intFromPtr(&cie_bytes[fbr.pos]), pc_rel_offset),
                        .follow_indirect = is_runtime,
                    });
                },
                'R' => {
                    fde_pointer_enc = try fbr.readByte();
                },
                'S', 'B', 'G' => {},
                else => return bad(),
            }
        }

        // aug_data_len can include padding so the CIE ends on an address boundary
        fbr.pos = aug_data_start + aug_data_len;
        break :blk aug_str;
    } else &[_]u8{};

    const initial_instructions = cie_bytes[fbr.pos..];
    return .{
        .length_offset = length_offset,
        .version = version,
        .address_size = address_size,
        .format = format,
        .segment_selector_size = segment_selector_size,
        .code_alignment_factor = code_alignment_factor,
        .data_alignment_factor = data_alignment_factor,
        .return_address_register = return_address_register,
        .aug_str = aug_str,
        .aug_data = aug_data,
        .lsda_pointer_enc = lsda_pointer_enc,
        .personality_enc = personality_enc,
        .personality_routine_pointer = personality_routine_pointer,
        .fde_pointer_enc = fde_pointer_enc,
        .initial_instructions = initial_instructions,
    };
}