loadOFile

fn loadOFile(gpa: Allocator, io: Io, o_file_name: []const u8) !OFile {
    const all_mapped_memory, const mapped_ofile = map: {
        const open_paren = paren: {
            if (std.mem.endsWith(u8, o_file_name, ")")) {
                if (std.mem.findScalarLast(u8, o_file_name, '(')) |i| {
                    break :paren i;
                }
            }
            // Not an archive, just a normal path to a .o file
            const m = try mapDebugInfoFile(io, o_file_name);
            break :map .{ m, m };
        };

        // We have the form 'path/to/archive.a(entry.o)'. Map the archive and find the object file in question.

        const archive_path = o_file_name[0..open_paren];
        const target_name_in_archive = o_file_name[open_paren + 1 .. o_file_name.len - 1];
        const mapped_archive = try mapDebugInfoFile(io, archive_path);
        errdefer posix.munmap(mapped_archive);

        var ar_reader: Io.Reader = .fixed(mapped_archive);
        const ar_magic = ar_reader.take(8) catch return error.InvalidMachO;
        if (!std.mem.eql(u8, ar_magic, "!<arch>\n")) return error.InvalidMachO;
        while (true) {
            if (ar_reader.seek == ar_reader.buffer.len) return error.MissingDebugInfo;

            const raw_name = ar_reader.takeArray(16) catch return error.InvalidMachO;
            ar_reader.discardAll(12 + 6 + 6 + 8) catch return error.InvalidMachO;
            const raw_size = ar_reader.takeArray(10) catch return error.InvalidMachO;
            const file_magic = ar_reader.takeArray(2) catch return error.InvalidMachO;
            if (!std.mem.eql(u8, file_magic, "`\n")) return error.InvalidMachO;

            const size = std.fmt.parseInt(u32, mem.sliceTo(raw_size, ' '), 10) catch return error.InvalidMachO;
            const raw_data = ar_reader.take(size) catch return error.InvalidMachO;

            const entry_name: []const u8, const entry_contents: []const u8 = entry: {
                if (!std.mem.startsWith(u8, raw_name, "#1/")) {
                    break :entry .{ mem.sliceTo(raw_name, '/'), raw_data };
                }
                const len = std.fmt.parseInt(u32, mem.sliceTo(raw_name[3..], ' '), 10) catch return error.InvalidMachO;
                if (len > size) return error.InvalidMachO;
                break :entry .{ mem.sliceTo(raw_data[0..len], 0), raw_data[len..] };
            };

            if (std.mem.eql(u8, entry_name, target_name_in_archive)) {
                break :map .{ mapped_archive, entry_contents };
            }
        }
    };
    errdefer posix.munmap(all_mapped_memory);

    var r: Io.Reader = .fixed(mapped_ofile);
    const hdr = r.takeStruct(macho.mach_header_64, .little) catch |err| switch (err) {
        error.ReadFailed => unreachable,
        error.EndOfStream => return error.InvalidMachO,
    };
    if (hdr.magic != std.macho.MH_MAGIC_64) return error.InvalidMachO;

    const seg_cmd: macho.LoadCommandIterator.LoadCommand, const symtab_cmd: macho.symtab_command = cmds: {
        var seg_cmd: ?macho.LoadCommandIterator.LoadCommand = null;
        var symtab_cmd: ?macho.symtab_command = null;
        var it: macho.LoadCommandIterator = try .init(&hdr, mapped_ofile[@sizeOf(macho.mach_header_64)..]);
        while (try it.next()) |lc| switch (lc.hdr.cmd) {
            .SEGMENT_64 => seg_cmd = lc,
            .SYMTAB => symtab_cmd = lc.cast(macho.symtab_command) orelse return error.InvalidMachO,
            else => {},
        };
        break :cmds .{
            seg_cmd orelse return error.MissingDebugInfo,
            symtab_cmd orelse return error.MissingDebugInfo,
        };
    };

    if (mapped_ofile.len < symtab_cmd.stroff + symtab_cmd.strsize) return error.InvalidMachO;
    if (mapped_ofile[symtab_cmd.stroff + symtab_cmd.strsize - 1] != 0) return error.InvalidMachO;
    const strtab = mapped_ofile[symtab_cmd.stroff..][0 .. symtab_cmd.strsize - 1];

    const n_sym_bytes = symtab_cmd.nsyms * @sizeOf(macho.nlist_64);
    if (mapped_ofile.len < symtab_cmd.symoff + n_sym_bytes) return error.InvalidMachO;
    const symtab_raw: []align(1) const macho.nlist_64 = @ptrCast(mapped_ofile[symtab_cmd.symoff..][0..n_sym_bytes]);

    // TODO handle tentative (common) symbols
    var symbols_by_name: std.array_hash_map.Custom(u32, void, void, true) = .empty;
    defer symbols_by_name.deinit(gpa);
    try symbols_by_name.ensureUnusedCapacity(gpa, @intCast(symtab_raw.len));
    for (symtab_raw, 0..) |sym_raw, sym_index| {
        var sym = sym_raw;
        if (builtin.cpu.arch.endian() != .little) std.mem.byteSwapAllFields(macho.nlist_64, &sym);
        if (sym.n_strx == 0) continue;
        switch (sym.n_type.bits.type) {
            .undf => continue, // includes tentative symbols
            .abs => continue,
            else => {},
        }
        const sym_name = mem.sliceTo(strtab[sym.n_strx..], 0);
        const gop = symbols_by_name.getOrPutAssumeCapacityAdapted(
            @as([]const u8, sym_name),
            @as(OFile.SymbolAdapter, .{ .strtab = strtab, .symtab_raw = symtab_raw }),
        );
        if (gop.found_existing) return error.InvalidMachO;
        gop.key_ptr.* = @intCast(sym_index);
    }

    const dwarf = try loadDwarfFromSections(gpa, mapped_ofile, seg_cmd.getSections());

    return .{
        .mapped_memory = all_mapped_memory,
        .dwarf = dwarf,
        .strtab = strtab,
        .symtab_raw = symtab_raw,
        .symbols_by_name = symbols_by_name.move(),
    };
}