From 5074dbff99c13f2a430074c2e4d5cc810979efbe Mon Sep 17 00:00:00 2001
From: "Andrei I. Holub" <andrei.holub@gmail.com>
Date: Fri, 10 Jul 2026 21:46:54 -0400
Subject: [PATCH] Fix Emscripten 6 compatibility: restore ERRNO_CODES and bind
 FS method context Emscripten 6 made two breaking changes that break
 BrowserFS's EmscriptenFS shim:
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1. ERRNO_CODES is no longer a global (removed in emscripten >=3.x).
   Pass FS, PATH, and an explicit errno map to EmscriptenFS so
   BrowserFS can map errno names to numbers.
2. FS node_ops/stream_ops methods are now called as bare functions
   (e.g. getattr(node) instead of node_ops.getattr(node)), losing
   . Bind all prototype methods on the node_ops and stream_ops
   wrapper instances so they retain their context.

Without these fixes, accessing files under /emulator throws:
  TypeError: can't access property fs, this is undefined
  at $.getattr → fstat → ___syscall_fstat64
---
 loader.js | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/loader.js b/loader.js
index 74d302ba..6251bd54 100644
--- a/loader.js
+++ b/loader.js
@@ -1273,7 +1273,39 @@ var Module = null;
                 preInit: function () {
                            // Re-initialize BFS to just use the writable in-memory storage.
                            BrowserFS.initialize(game_data.fs);
-                           var BFS = new BrowserFS.EmscriptenFS();
+                           // Newer emscripten (>=3.x) no longer exposes ERRNO_CODES as a
+                           // global, and FS/PATH are module-scoped vars that happen to be
+                           // globals because mame.js is a plain top-level script. Pass them
+                           // explicitly to EmscriptenFS so BrowserFS can map node errno
+                           // names (e.g. ENOENT) to numbers.
+                           var ERRNO_CODES_MAP = {
+                             EPERM: 1, ENOENT: 2, ESRCH: 3, EINTR: 4, EIO: 5, ENXIO: 6,
+                             E2BIG: 7, ENOEXEC: 8, EBADF: 9, ECHILD: 10, EAGAIN: 11,
+                             ENOMEM: 12, EACCES: 13, EFAULT: 14, EBUSY: 16, EEXIST: 17,
+                             EXDEV: 18, ENODEV: 19, ENOTDIR: 20, EISDIR: 21, EINVAL: 22,
+                             ENFILE: 23, EMFILE: 24, ENOTTY: 25, ETXTBSY: 26, EFBIG: 27,
+                             ENOSPC: 28, ESPIPE: 29, EROFS: 30, EMLINK: 31, EPIPE: 32,
+                             EDOM: 33, ERANGE: 34, ENOTEMPTY: 39, ELOOP: 40,
+                             ENAMETOOLONG: 37, ENOSYS: 38
+                           };
+                           var BFS = new BrowserFS.EmscriptenFS(FS, PATH, ERRNO_CODES_MAP);
+                           // Emscripten 6+ extracts node_ops/stream_ops methods and
+                           // calls them as bare functions (e.g. getattr(node) instead
+                           // of node_ops.getattr(node)), losing `this`. Bind every
+                           // method on the node_ops and stream_ops wrapper objects so
+                           // they retain their context regardless of call convention.
+                           ["node_ops", "stream_ops"].forEach(function (key) {
+                             var ops = BFS[key];
+                             if (!ops) return;
+                             Object.getOwnPropertyNames(
+                               Object.getPrototypeOf(ops)
+                             ).forEach(function (name) {
+                               if (name !== "constructor" &&
+                                   typeof ops[name] === "function") {
+                                 ops[name] = ops[name].bind(ops);
+                               }
+                             });
+                           });
                            // Mount the file system into Emscripten.
                            FS.mkdir('/emulator');
                            FS.mount(BFS, {root: '/'}, '/emulator');