From d53f1ed5a7041810a9e5afaa19f866f01cae8230 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Tue, 3 Feb 2026 14:24:40 -0800
Subject: [PATCH 1/2] Fix fd_sync under pthreads

This function is marked as `__async: 'auto'` which means it should
return a promise when run in proxied mode on the main thread.  However
it wasn't always returning a promise.   Adding the `async` keyword
is the simplest way to ensure it always returns a promise.

Also, update the `wrapSyscallFunction` function to preserve the async
keyword.

Replaces: #26209
---
 src/lib/libcore.js         |  2 +-
 src/lib/libwasi.js         | 23 ++++++++++++++---------
 test/fs/test_memfs_fsync.c |  5 +++--
 test/test_other.py         | 12 +++++++++++-
 4 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/src/lib/libcore.js b/src/lib/libcore.js
index 1355a7b075863..1fb5e90f2597b 100644
--- a/src/lib/libcore.js
+++ b/src/lib/libcore.js
@@ -2605,7 +2605,7 @@ function wrapSyscallFunction(x, library, isWasi) {
   post = handler + post;
 
   if (pre || post) {
-    t = modifyJSFunction(t, (args, body) => `function (${args}) {\n${pre}${body}${post}}\n`);
+    t = modifyJSFunction(t, (args, body, async_) => `${async_}function (${args}) {\n${pre}${body}${post}}\n`);
   }
 
   library[x] = eval('(' + t + ')');
diff --git a/src/lib/libwasi.js b/src/lib/libwasi.js
index 55a32db216022..bd85bac000886 100644
--- a/src/lib/libwasi.js
+++ b/src/lib/libwasi.js
@@ -540,27 +540,32 @@ var WasiLibrary = {
     return 0;
   },
 
+#if SYSCALLS_REQUIRE_FILESYSTEM
   fd_sync__async: 'auto',
   fd_sync: (fd) => {
-#if SYSCALLS_REQUIRE_FILESYSTEM
     var stream = SYSCALLS.getStreamFromFD(fd);
     var rtn = stream.stream_ops?.fsync?.(stream);
-#if ASYNCIFY
-    var mount = stream.node.mount;
-    if (mount.type.syncfs) {
-      return new Promise((resolve) => {
+#if ASYNCIFY || PTHREADS
+    return new Promise((resolve) => {
+      var mount = stream.node.mount;
+      if (mount && mount.type.syncfs) {
         mount.type.syncfs(mount, false, (err) => resolve(err ? {{{ cDefs.EIO }}} : 0));
-      });
-    }
-#endif // ASYNCIFY
+      } else {
+        resolve(rtn);
+      }
+    });
+#else
     return rtn;
+#endif // ASYNCIFY || PTHREADS
+  },
 #else // SYSCALLS_REQUIRE_FILESYSTEM
+  fd_sync: (fd) => {
 #if ASSERTIONS
     abort('fd_sync called without SYSCALLS_REQUIRE_FILESYSTEM');
 #endif
     return {{{ cDefs.ENOSYS }}};
-#endif // SYSCALLS_REQUIRE_FILESYSTEM
   },
+#endif // SYSCALLS_REQUIRE_FILESYSTEM
 
   // random.h
 
diff --git a/test/fs/test_memfs_fsync.c b/test/fs/test_memfs_fsync.c
index 67d9aafe11947..0933395253ba4 100644
--- a/test/fs/test_memfs_fsync.c
+++ b/test/fs/test_memfs_fsync.c
@@ -23,10 +23,10 @@ int main() {
   struct stat st;
 
   // a file whose contents are just 'az'
-  rtn = stat("/wakaka.txt", &st);
+  rtn = stat("wakaka.txt", &st);
   assert(rtn == -1 && errno == ENOENT);
 
-  fd = open("/wakaka.txt", O_RDWR | O_CREAT, 0666);
+  fd = open("wakaka.txt", O_RDWR | O_CREAT, 0666);
   assert(fd >= 0);
 
   rtn = write(fd, "az", 2);
@@ -38,5 +38,6 @@ int main() {
   rtn = close(fd);
   assert(rtn == 0);
 
+  printf("success\n");
   return 0;
 }
diff --git a/test/test_other.py b/test/test_other.py
index 373fb7110c68d..1e50725b06981 100644
--- a/test/test_other.py
+++ b/test/test_other.py
@@ -58,6 +58,7 @@
   also_with_asan,
   also_with_minimal_runtime,
   also_with_modularize,
+  also_with_nodefs_both,
   also_with_noderawfs,
   also_with_standalone_wasm,
   also_with_wasm2js,
@@ -5525,7 +5526,16 @@ def test_dashM_respect_dashO(self):
   @with_all_fs
   @crossplatform
   def test_fs_bad_lookup(self):
-    self.do_runf(path_from_root('test/fs/test_fs_bad_lookup.c'), expected_output='ok')
+    self.do_runf('fs/test_fs_bad_lookup.c', 'ok')
+
+  @also_with_nodefs_both
+  @crossplatform
+  @parameterized({
+    '': ([],),
+    'pthreads': (['-pthread', '-sPROXY_TO_PTHREAD', '-sEXIT_RUNTIME'],),
+  })
+  def test_fsync(self, args):
+    self.do_runf('fs/test_memfs_fsync.c', 'success', cflags=args)
 
   @with_all_fs
   @crossplatform

From 0899a4239af0832985b3609434b4b9234c1f780c Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Wed, 4 Feb 2026 13:33:06 -0800
Subject: [PATCH 2/2] Update src/lib/libwasi.js

Co-authored-by: Alon Zakai <alonzakai@gmail.com>
---
 src/lib/libwasi.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/lib/libwasi.js b/src/lib/libwasi.js
index bd85bac000886..bb67581f269a6 100644
--- a/src/lib/libwasi.js
+++ b/src/lib/libwasi.js
@@ -548,7 +548,7 @@ var WasiLibrary = {
 #if ASYNCIFY || PTHREADS
     return new Promise((resolve) => {
       var mount = stream.node.mount;
-      if (mount && mount.type.syncfs) {
+      if (mount?.type.syncfs) {
         mount.type.syncfs(mount, false, (err) => resolve(err ? {{{ cDefs.EIO }}} : 0));
       } else {
         resolve(rtn);