it fucking works lmao

src/elf.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const oldzig = @import("oldzig.zig");
 
 // Cool website for ELF info:
 // https://www.man7.org/linux/man-pages/man5/elf.5.html
@@ -253,6 +254,50 @@ pub fn alignSegments(map: *DolMap) void {
     }
 }
 
+pub fn writeDOL(map: DolMap, input: std.fs.File, output: std.fs.File) !void {
+    const reader = input.reader();
+    const writer = output.writer();
+
+    // Write header
+    try oldzig.writeStructEndian(writer, map.header, std.builtin.Endian.big);
+
+    // Create buffer for pump
+    var fifo = std.fifo.LinearFifo(u8, .{ .Static = 1024 * 1024 }).init();
+    defer fifo.deinit();
+
+    // Copy over text segments
+    for (0..map.text_cnt) |i| {
+        // Seek to text segment
+        try input.seekTo(map.text_elf_off[i]);
+
+        // Create limited reader to segment size
+        var limitedReader = std.io.limitedReader(reader, map.header.text_size[i]);
+
+        // Seek to destination
+        try output.seekTo(map.header.text_off[i]);
+
+        // Copy segment
+        std.debug.print("Copying text segment {d} at 0x{x} -> 0x{x}\n", .{ i, map.header.text_addr[i], map.header.text_off[i] });
+        try fifo.pump(&limitedReader, writer);
+    }
+
+    // Copy over data segments
+    for (0..map.data_cnt) |i| {
+        // Seek to text segment
+        try input.seekTo(map.data_elf_off[i]);
+
+        // Create limited reader to segment size
+        var limitedReader = std.io.limitedReader(reader, map.header.data_size[i]);
+
+        // Seek to destination
+        try output.seekTo(map.header.data_off[i]);
+
+        // Copy segment
+        std.debug.print("Copying data segment {d} at 0x{x} -> 0x{x}\n", .{ i, map.header.data_addr[i], map.header.data_off[i] });
+        try fifo.pump(&limitedReader, writer);
+    }
+}
+
 fn checkELFHeader(header: ELFHeader) !void {
     // Check magic
     if (!std.mem.eql(u8, header.e_ident[0..4], ELFMagic)) {

src/main.zig

@@ -18,11 +18,17 @@ pub fn main() !void {
 
     const inputPath = args[1];
     const outputPath = args[2];
-    _ = outputPath; // autofix
 
     // Read input
     const input = try std.fs.cwd().openFile(inputPath, .{});
-
+    defer input.close();
     var map = try elf.readELF(input);
+
+    // Align segments to 64 byte boundaries
     elf.alignSegments(&map);
+
+    // Write header and copy over segments from input
+    const output = try std.fs.cwd().createFile(outputPath, .{});
+    defer output.close();
+    try elf.writeDOL(map, input, output);
 }

src/oldzig.zig

@@ -0,0 +1,13 @@
+const native_endian = @import("builtin").target.cpu.arch.endian();
+const std = @import("std");
+
+// This is in nightly but they haven't been making builds for a while
+pub fn writeStructEndian(writer: anytype, value: anytype, endian: std.builtin.Endian) anyerror!void {
+    if (native_endian == endian) {
+        return writer.writeStruct(value);
+    } else {
+        var copy = value;
+        std.mem.byteSwapAllFields(@TypeOf(value), &copy);
+        return writer.writeStruct(copy);
+    }
+}