From 6e03994f426d44e2e5ed7b8a824a61bb80f1cd1b Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 17:32:34 +0000
Subject: [PATCH 01/28] Pass --generate-threading-helpers for WASIP3

---
 cmake/bindings.cmake | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/cmake/bindings.cmake b/cmake/bindings.cmake
index 15b8d0593..490aa5df9 100644
--- a/cmake/bindings.cmake
+++ b/cmake/bindings.cmake
@@ -15,8 +15,8 @@ if(WIT_BINDGEN_EXECUTABLE)
     OUTPUT_VARIABLE WIT_BINDGEN_VERSION
     OUTPUT_STRIP_TRAILING_WHITESPACE)
 
-  if (NOT (WIT_BINDGEN_VERSION MATCHES "0\\.51\\.0"))
-    message(WARNING "wit-bindgen version 0.51.0 is required, found: ${WIT_BINDGEN_VERSION}")
+  if (NOT (WIT_BINDGEN_VERSION MATCHES "0\\.53\\.1"))
+    message(WARNING "wit-bindgen version 0.53.1 is required, found: ${WIT_BINDGEN_VERSION}")
     set(WIT_BINDGEN_EXECUTABLE "")
   endif()
 endif()
@@ -26,7 +26,7 @@ if (NOT WIT_BINDGEN_EXECUTABLE)
   ba_download(
     wit-bindgen
     "https://github.com/bytecodealliance/wit-bindgen"
-    "0.51.0"
+    "0.53.1"
   )
   ExternalProject_Get_Property(wit-bindgen SOURCE_DIR)
   set(wit_bindgen "${SOURCE_DIR}/wit-bindgen")
@@ -87,6 +87,7 @@ add_custom_target(
       --rename-world wasip3
       --type-section-suffix __wasi_libc
       --world wasi:cli/imports@${wasip3-version}
+      --generate-threading-helpers
       --rename wasi:clocks/monotonic-clock@${wasip3-version}=monotonic_clock
       --rename wasi:clocks/system-clock@${wasip3-version}=system_clock
       --rename wasi:filesystem/preopens@${wasip3-version}=filesystem_preopens
@@ -133,4 +134,4 @@ function(wit_bindgen_edit p)
 endfunction()
 
 wit_bindgen_edit(p2)
-wit_bindgen_edit(p3)
+wit_bindgen_edit(p3)
\ No newline at end of file

From 776691c31fb255f1ce19160353d1a2bfced928dd Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 17:33:13 +0000
Subject: [PATCH 02/28] Newline

---
 cmake/bindings.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/bindings.cmake b/cmake/bindings.cmake
index 490aa5df9..ed1236ec0 100644
--- a/cmake/bindings.cmake
+++ b/cmake/bindings.cmake
@@ -134,4 +134,4 @@ function(wit_bindgen_edit p)
 endfunction()
 
 wit_bindgen_edit(p2)
-wit_bindgen_edit(p3)
\ No newline at end of file
+wit_bindgen_edit(p3)

From 1e176a0b734ca86df532fc741367c20cdc8c4717 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 17:35:06 +0000
Subject: [PATCH 03/28] Generate bindings

---
 .../headers/public/wasi/__generated_wasip2.h  |   2 +-
 .../headers/public/wasi/__generated_wasip3.h  |  18 +++-
 libc-bottom-half/sources/wasip2.c             |   2 +-
 .../sources/wasip2_component_type.o           | Bin 10846 -> 10846 bytes
 libc-bottom-half/sources/wasip3.c             | 101 +++++++++++++++++-
 .../sources/wasip3_component_type.o           | Bin 8099 -> 8099 bytes
 6 files changed, 119 insertions(+), 4 deletions(-)

diff --git a/libc-bottom-half/headers/public/wasi/__generated_wasip2.h b/libc-bottom-half/headers/public/wasi/__generated_wasip2.h
index e4f14db97..2a8718739 100644
--- a/libc-bottom-half/headers/public/wasi/__generated_wasip2.h
+++ b/libc-bottom-half/headers/public/wasi/__generated_wasip2.h
@@ -1,4 +1,4 @@
-// Generated by `wit-bindgen` 0.51.0. DO NOT EDIT!
+// Generated by `wit-bindgen` 0.53.1. DO NOT EDIT!
 #ifndef __BINDINGS_WASIP2_H
 #define __BINDINGS_WASIP2_H
 #ifdef __cplusplus
diff --git a/libc-bottom-half/headers/public/wasi/__generated_wasip3.h b/libc-bottom-half/headers/public/wasi/__generated_wasip3.h
index f9f04db25..2a5d526ce 100644
--- a/libc-bottom-half/headers/public/wasi/__generated_wasip3.h
+++ b/libc-bottom-half/headers/public/wasi/__generated_wasip3.h
@@ -1,4 +1,4 @@
-// Generated by `wit-bindgen` 0.51.0. DO NOT EDIT!
+// Generated by `wit-bindgen` 0.53.1. DO NOT EDIT!
 #ifndef __BINDINGS_WASIP3_H
 #define __BINDINGS_WASIP3_H
 #ifdef __cplusplus
@@ -80,6 +80,22 @@ void wasip3_context_set_0(void* value);
 void wasip3_thread_yield(void);
 
 
+void* wasip3_context_get_1(void);
+void wasip3_context_set_1(void* value);
+uint32_t wasip3_thread_yield_cancellable(void);
+uint32_t wasip3_thread_index(void);
+uint32_t wasip3_thread_new_indirect(void (*start_function)(void*), void* arg);
+void wasip3_thread_suspend_to(uint32_t thread);
+uint32_t wasip3_thread_suspend_to_cancellable(uint32_t thread);
+void wasip3_thread_suspend_to_suspended(uint32_t thread);
+uint32_t wasip3_thread_suspend_to_suspended_cancellable(uint32_t thread);
+void wasip3_thread_unsuspend(uint32_t thread);
+void wasip3_thread_yield_to_suspended(uint32_t thread);
+uint32_t wasip3_thread_yield_to_suspended_cancellable(uint32_t thread);
+void wasip3_thread_suspend(void);
+uint32_t wasip3_thread_suspend_cancellable(void);
+
+
 
 typedef struct {
   wasip3_string_t f0;
diff --git a/libc-bottom-half/sources/wasip2.c b/libc-bottom-half/sources/wasip2.c
index ef3f67ba2..da2a5f141 100644
--- a/libc-bottom-half/sources/wasip2.c
+++ b/libc-bottom-half/sources/wasip2.c
@@ -1,4 +1,4 @@
-// Generated by `wit-bindgen` 0.51.0. DO NOT EDIT!
+// Generated by `wit-bindgen` 0.53.1. DO NOT EDIT!
 #include "wasi/wasip2.h"
 #include <stdlib.h>
 #include <string.h>
diff --git a/libc-bottom-half/sources/wasip2_component_type.o b/libc-bottom-half/sources/wasip2_component_type.o
index abbd242946ebf1c4c3b4933cb92293b05f6a0461..5f85d8c870715ab8d86771b0d2e9457b58533518 100644
GIT binary patch
delta 36
rcmcZ?axY{9x0Zydo*{2}W{GZ6W?o8qYMyQ~n}MFGv7X^%Wi4v}=zj|_

delta 36
rcmcZ?axY{9x0Zy7o&j%pW{GZ6W?o8qYMyQ~n}MFGp`O8HWi4v}=r#*1

diff --git a/libc-bottom-half/sources/wasip3.c b/libc-bottom-half/sources/wasip3.c
index 26b92a86a..8b0f3d960 100644
--- a/libc-bottom-half/sources/wasip3.c
+++ b/libc-bottom-half/sources/wasip3.c
@@ -1,4 +1,4 @@
-// Generated by `wit-bindgen` 0.51.0. DO NOT EDIT!
+// Generated by `wit-bindgen` 0.53.1. DO NOT EDIT!
 #include "wasi/wasip3.h"
 #include <stdlib.h>
 #include <string.h>
@@ -1142,6 +1142,105 @@ void wasip3_thread_yield(void) {
 }
 
 
+__attribute__((__import_module__("$root"), __import_name__("[context-get-1]")))
+extern void* __context_get_1(void);
+
+void* wasip3_context_get_1(void) {
+  return __context_get_1();
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[context-set-1]")))
+extern void __context_set_1(void*);
+
+void wasip3_context_set_1(void* value) {
+  __context_set_1(value);
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[cancellable][thread-yield]")))
+extern uint32_t __thread_yield_cancellable(void);
+
+uint32_t wasip3_thread_yield_cancellable(void) {
+  return __thread_yield_cancellable();
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[thread-index]")))
+extern uint32_t __thread_index(void);
+
+uint32_t wasip3_thread_index(void) {
+  return __thread_index();
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[thread-new-indirect-v0]")))
+extern uint32_t __thread_new_indirect(uint32_t, void*);
+
+uint32_t wasip3_thread_new_indirect(void (*start_function)(void*), void* arg) {
+  return __thread_new_indirect((uint32_t)(uintptr_t)start_function, arg
+  );
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[thread-suspend-to-suspended]")))
+extern uint32_t __thread_suspend_to_suspended(uint32_t);
+
+void wasip3_thread_suspend_to_suspended(uint32_t thread) {
+  __thread_suspend_to_suspended(thread);
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[cancellable][thread-suspend-to-suspended]")))
+extern uint32_t __thread_suspend_to_suspended_cancellable(uint32_t);
+
+uint32_t wasip3_thread_suspend_to_suspended_cancellable(uint32_t thread) {
+  return __thread_suspend_to_suspended_cancellable(thread);
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[thread-suspend-to]")))
+extern uint32_t __thread_suspend_to(uint32_t);
+
+void wasip3_thread_suspend_to(uint32_t thread) {
+  __thread_suspend_to(thread);
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[cancellable][thread-suspend-to]")))
+extern uint32_t __thread_suspend_to_cancellable(uint32_t);
+
+uint32_t wasip3_thread_suspend_to_cancellable(uint32_t thread) {
+  return __thread_suspend_to_cancellable(thread);
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[thread-unsuspend]")))
+extern void __thread_unsuspend(uint32_t);
+
+void wasip3_thread_unsuspend(uint32_t thread) {
+  __thread_unsuspend(thread);
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[thread-yield-to-suspended]")))
+extern uint32_t __thread_yield_to_suspended(uint32_t);
+
+void wasip3_thread_yield_to_suspended(uint32_t thread) {
+  __thread_yield_to_suspended(thread);
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[cancellable][thread-yield-to-suspended]")))
+extern uint32_t __thread_yield_to_suspended_cancellable(uint32_t);
+
+uint32_t wasip3_thread_yield_to_suspended_cancellable(uint32_t thread) {
+  return __thread_yield_to_suspended_cancellable(thread);
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[thread-suspend]")))
+extern uint32_t __thread_suspend(void);
+
+void wasip3_thread_suspend(void) {
+  __thread_suspend();
+}
+
+__attribute__((__import_module__("$root"), __import_name__("[cancellable][thread-suspend]")))
+extern uint32_t __thread_suspend_cancellable(void);
+uint32_t wasip3_thread_suspend_cancellable(void) {
+  return __thread_suspend_cancellable();
+}
+
+
 
 // Component Adapters
 
diff --git a/libc-bottom-half/sources/wasip3_component_type.o b/libc-bottom-half/sources/wasip3_component_type.o
index 68f4f3604b601e2b750b65bc5532d01a799cf67a..e92156ffbbf4554b4083803e095e23a5cdefae0b 100644
GIT binary patch
delta 36
rcmZ2%zu105fV_mMo*{2}W{GZ6W?o8qYMyQ~n}MFGv7X`N40&q++LH?f

delta 36
rcmZ2%zu105fV_l>o&j%pW{GZ6W?o8qYMyQ~n}MFGp`O9y40&q++DZ!m


From 418a2cf8d9ce5b3cb2cb6829562bd80c15d34d26 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 18:05:40 +0000
Subject: [PATCH 04/28] Locks

---
 CMakeLists.txt                                |  1 +
 .../cloudlibc/src/libc/sched/sched_yield.c    |  8 ++++
 .../headers/public/wasi/version.h.in          |  1 +
 libc-bottom-half/sources/getcwd.c             | 16 +++----
 libc-bottom-half/sources/preopens.c           | 30 ++++++------
 libc-top-half/musl/src/exit/at_quick_exit.c   | 16 ++++---
 libc-top-half/musl/src/exit/atexit.c          | 20 ++++----
 libc-top-half/musl/src/internal/locale_impl.h |  3 +-
 libc-top-half/musl/src/internal/lock.h        | 47 ++++++++++++++++---
 .../musl/src/internal/pthread_impl.h          | 35 +++++---------
 libc-top-half/musl/src/internal/stdio_impl.h  | 14 +++++-
 libc-top-half/musl/src/locale/locale_map.c    |  4 +-
 libc-top-half/musl/src/locale/newlocale.c     |  4 +-
 libc-top-half/musl/src/locale/setlocale.c     | 10 ++--
 .../musl/src/malloc/oldmalloc/malloc.c        | 11 +++++
 libc-top-half/musl/src/prng/random.c          | 22 +++++----
 libc-top-half/musl/src/stdio/__fdopen.c       |  2 +-
 libc-top-half/musl/src/stdio/__fopen_rb_ca.c  |  2 +-
 libc-top-half/musl/src/stdio/__lockfile.c     | 24 ++++++++++
 libc-top-half/musl/src/stdio/fmemopen.c       |  2 +-
 libc-top-half/musl/src/stdio/ftrylockfile.c   | 38 +++++++++++++--
 libc-top-half/musl/src/stdio/getc.h           | 13 ++++-
 libc-top-half/musl/src/stdio/ofl.c            |  8 ++--
 libc-top-half/musl/src/stdio/open_memstream.c |  2 +-
 .../musl/src/stdio/open_wmemstream.c          |  2 +-
 libc-top-half/musl/src/stdio/putc.h           | 18 ++++++-
 libc-top-half/musl/src/stdio/stderr.c         |  2 +-
 libc-top-half/musl/src/stdio/stdin.c          |  2 +-
 libc-top-half/musl/src/stdio/stdout.c         |  2 +-
 libc-top-half/musl/src/stdio/vdprintf.c       |  2 +-
 libc-top-half/musl/src/stdio/vsscanf.c        |  5 +-
 libc-top-half/musl/src/stdio/vswscanf.c       |  5 +-
 libc-top-half/musl/src/stdlib/wcstod.c        |  2 +-
 libc-top-half/musl/src/stdlib/wcstol.c        |  2 +-
 .../musl/src/thread/coop-threads/__lock.c     | 38 +++++++++++++++
 .../musl/src/thread/coop-threads/__wait.c     | 47 +++++++++++++++++++
 36 files changed, 344 insertions(+), 116 deletions(-)
 create mode 100644 libc-top-half/musl/src/thread/coop-threads/__lock.c
 create mode 100644 libc-top-half/musl/src/thread/coop-threads/__wait.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c48f41b15..86793fdc8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -139,6 +139,7 @@ elseif(WASI STREQUAL "p2")
   set(__wasip2__ ON)
 elseif(WASI STREQUAL "p3")
   set(__wasip3__ ON)
+  set(__wasi_cooperative_threads__ ON)
 else()
   message(FATAL_ERROR "Unknown WASI version: ${WASI}")
 endif()
diff --git a/libc-bottom-half/cloudlibc/src/libc/sched/sched_yield.c b/libc-bottom-half/cloudlibc/src/libc/sched/sched_yield.c
index fc13322b6..c4b298e33 100644
--- a/libc-bottom-half/cloudlibc/src/libc/sched/sched_yield.c
+++ b/libc-bottom-half/cloudlibc/src/libc/sched/sched_yield.c
@@ -7,6 +7,14 @@
 #include <sched.h>
 
 int sched_yield(void) {
+#ifdef __wasi_cooperative_threads__
+  #ifdef __wasip3__
+    wasip3_thread_yield();
+    return 0;
+  #else
+    #error "Unknown WASI version"
+  #endif
+#elif defined(__wasip1__)
 #ifdef __wasip1__
   __wasi_errno_t error = __wasi_sched_yield();
   if (error != 0) {
diff --git a/libc-bottom-half/headers/public/wasi/version.h.in b/libc-bottom-half/headers/public/wasi/version.h.in
index 2cca21efc..8da5d9991 100644
--- a/libc-bottom-half/headers/public/wasi/version.h.in
+++ b/libc-bottom-half/headers/public/wasi/version.h.in
@@ -10,6 +10,7 @@
 #cmakedefine __wasip1__
 #cmakedefine __wasip2__
 #cmakedefine __wasip3__
+#cmakedefine __wasi_cooperative_threads__
 
 #cmakedefine __wasi_sdk_major__ @__wasi_sdk_major__@
 #cmakedefine __wasi_sdk_version__ "@__wasi_sdk_version__@"
diff --git a/libc-bottom-half/sources/getcwd.c b/libc-bottom-half/sources/getcwd.c
index 8b0b0b746..576508620 100644
--- a/libc-bottom-half/sources/getcwd.c
+++ b/libc-bottom-half/sources/getcwd.c
@@ -7,32 +7,28 @@
 char *__wasilibc_cwd = "/";
 
 #ifdef _REENTRANT
-static volatile int lock[1];
-void __wasilibc_cwd_lock(void) { LOCK(lock); }
-void __wasilibc_cwd_unlock(void) { UNLOCK(lock); }
-#else
-#define __wasilibc_cwd_lock() (void)0
-#define __wasilibc_cwd_unlock() (void)0
+static __lock_t lock[1];
 #endif
 
 char *getcwd(char *buf, size_t size) {
-  __wasilibc_cwd_lock();
+  // Critical section contains no yield points, so we can use weak locks.
+  WEAK_LOCK(lock);
   if (!buf) {
     buf = strdup(__wasilibc_cwd);
     if (!buf) {
       errno = ENOMEM;
-      __wasilibc_cwd_unlock();
+      WEAK_UNLOCK(lock);
       return NULL;
     }
   } else {
     size_t len = strlen(__wasilibc_cwd);
     if (size < len + 1) {
       errno = ERANGE;
-      __wasilibc_cwd_unlock();
+      WEAK_UNLOCK(lock);
       return NULL;
     }
     strcpy(buf, __wasilibc_cwd);
   }
-  __wasilibc_cwd_unlock();
+  WEAK_UNLOCK(lock);
   return buf;
 }
diff --git a/libc-bottom-half/sources/preopens.c b/libc-bottom-half/sources/preopens.c
index cf91ac016..84738c53f 100644
--- a/libc-bottom-half/sources/preopens.c
+++ b/libc-bottom-half/sources/preopens.c
@@ -21,6 +21,12 @@
 #include <wasi/file_utils.h>
 #endif
 
+/// Access to the the above preopen must be protected in the presence of
+/// threads.
+#ifdef _REENTRANT
+static __lock_t lock[1];
+#endif
+
 #if defined(__wasip1__)
 typedef struct {
   __wasi_fd_t fd;
@@ -96,12 +102,6 @@ static preopen *preopens;
 static size_t num_preopens;
 static size_t preopen_capacity;
 
-/// Access to the the above preopen must be protected in the presence of
-/// threads.
-#ifdef _REENTRANT
-static volatile int lock[1];
-#endif
-
 #ifdef NDEBUG
 #define assert_invariants() // assertions disabled
 #else
@@ -220,11 +220,11 @@ static bool prefix_matches(const char *prefix, size_t prefix_len,
 /// This function takes ownership of `prefix`.
 static int internal_register_preopened_fd(__wasi_fd_t fd,
                                           const char *relprefix) {
-  LOCK(lock);
+  STRONG_LOCK(lock);
 
   int r = internal_register_preopened_fd_unlocked(fd, relprefix);
 
-  UNLOCK(lock);
+  STRONG_UNLOCK(lock);
 
   return r;
 }
@@ -263,7 +263,7 @@ int __wasilibc_find_abspath(const char *path, const char **abs_prefix,
   // recently added preopens take precedence over less recently addded ones.
   size_t match_len = 0;
   int fd = -1;
-  LOCK(lock);
+  STRONG_LOCK(lock);
   for (size_t i = num_preopens; i > 0; --i) {
     const preopen *pre = &preopens[i - 1];
     const char *prefix = pre->prefix;
@@ -278,7 +278,7 @@ int __wasilibc_find_abspath(const char *path, const char **abs_prefix,
       *abs_prefix = prefix;
     }
   }
-  UNLOCK(lock);
+  STRONG_UNLOCK(lock);
 
   if (fd == -1) {
     errno = ENOENT;
@@ -306,11 +306,11 @@ void __wasilibc_populate_preopens(void) {
     return;
   }
 
-  LOCK(lock);
+  STRONG_LOCK(lock);
 
   // Check whether another thread initialized the preopens already.
   if (preopens_populated) {
-    UNLOCK(lock);
+    STRONG_UNLOCK(lock);
     return;
   }
 
@@ -381,7 +381,7 @@ void __wasilibc_populate_preopens(void) {
   // Preopens are now initialized.
   preopens_populated = true;
 
-  UNLOCK(lock);
+  STRONG_UNLOCK(lock);
 
   return;
 #ifdef __wasip1__
@@ -393,7 +393,7 @@ void __wasilibc_populate_preopens(void) {
 }
 
 void __wasilibc_reset_preopens(void) {
-  LOCK(lock);
+  STRONG_LOCK(lock);
 
   if (num_preopens) {
     for (int i = 0; i < num_preopens; ++i) {
@@ -410,5 +410,5 @@ void __wasilibc_reset_preopens(void) {
 
   assert_invariants();
 
-  UNLOCK(lock);
+  STRONG_UNLOCK(lock);
 }
diff --git a/libc-top-half/musl/src/exit/at_quick_exit.c b/libc-top-half/musl/src/exit/at_quick_exit.c
index 429d0b033..8cfffc426 100644
--- a/libc-top-half/musl/src/exit/at_quick_exit.c
+++ b/libc-top-half/musl/src/exit/at_quick_exit.c
@@ -8,28 +8,30 @@
 static void (*funcs[COUNT])(void);
 static int count;
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-static volatile int lock[1];
-volatile int *const __at_quick_exit_lockptr = lock;
+// All locks here can be weak, because the locking is only needed to protect against
+// concurrent manipulation of the handler table, which hits no context switch points.
+static __lock_t lock[1];
+__lock_t *const __at_quick_exit_lockptr = lock;
 #endif
 
 void __funcs_on_quick_exit()
 {
 	void (*func)(void);
-	LOCK(lock);
+	WEAK_LOCK(lock);
 	while (count > 0) {
 		func = funcs[--count];
-		UNLOCK(lock);
+		WEAK_UNLOCK(lock);
 		func();
-		LOCK(lock);
+		WEAK_LOCK(lock);
 	}
 }
 
 int at_quick_exit(void (*func)(void))
 {
 	int r = 0;
-	LOCK(lock);
+	WEAK_LOCK(lock);
 	if (count == 32) r = -1;
 	else funcs[count++] = func;
-	UNLOCK(lock);
+	WEAK_UNLOCK(lock);
 	return r;
 }
diff --git a/libc-top-half/musl/src/exit/atexit.c b/libc-top-half/musl/src/exit/atexit.c
index 155292d0e..d52ae8267 100644
--- a/libc-top-half/musl/src/exit/atexit.c
+++ b/libc-top-half/musl/src/exit/atexit.c
@@ -22,20 +22,24 @@ static struct fl
 static int slot;
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-static volatile int lock[1];
-volatile int *const __atexit_lockptr = lock;
+#include "lock.h"
+
+// All locks here can be weak, because the locking is only needed to protect against
+// concurrent manipulation of the handler table, which hits no context switch points.
+__lock_t lock[1];
+__lock_t *const __atexit_lockptr = lock;
 #endif
 
 void __funcs_on_exit()
 {
 	void (*func)(void *), *arg;
-	LOCK(lock);
+	WEAK_LOCK(lock);
 	for (; head; head=head->next, slot=COUNT) while(slot-->0) {
 		func = head->f[slot];
 		arg = head->a[slot];
-		UNLOCK(lock);
+		WEAK_UNLOCK(lock);
 		func(arg);
-		LOCK(lock);
+		WEAK_LOCK(lock);
 	}
 }
 
@@ -45,7 +49,7 @@ void __cxa_finalize(void *dso)
 
 int __cxa_atexit(void (*func)(void *), void *arg, void *dso)
 {
-	LOCK(lock);
+	WEAK_LOCK(lock);
 
 	/* Defer initialization of head so it can be in BSS */
 	if (!head) head = &builtin;
@@ -54,7 +58,7 @@ int __cxa_atexit(void (*func)(void *), void *arg, void *dso)
 	if (slot==COUNT) {
 		struct fl *new_fl = calloc(sizeof(struct fl), 1);
 		if (!new_fl) {
-			UNLOCK(lock);
+			WEAK_UNLOCK(lock);
 			return -1;
 		}
 		new_fl->next = head;
@@ -67,7 +71,7 @@ int __cxa_atexit(void (*func)(void *), void *arg, void *dso)
 	head->a[slot] = arg;
 	slot++;
 
-	UNLOCK(lock);
+	WEAK_UNLOCK(lock);
 	return 0;
 }
 
diff --git a/libc-top-half/musl/src/internal/locale_impl.h b/libc-top-half/musl/src/internal/locale_impl.h
index 88f5dcf8f..b792f8d0e 100644
--- a/libc-top-half/musl/src/internal/locale_impl.h
+++ b/libc-top-half/musl/src/internal/locale_impl.h
@@ -18,7 +18,8 @@ struct __locale_map {
 };
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-extern hidden volatile int __locale_lock[1];
+#include "lock.h"
+extern hidden __lock_t __locale_lock[1];
 #endif
 
 extern hidden const struct __locale_map __c_dot_utf8;
diff --git a/libc-top-half/musl/src/internal/lock.h b/libc-top-half/musl/src/internal/lock.h
index 29787fb1f..3e5a0a603 100644
--- a/libc-top-half/musl/src/internal/lock.h
+++ b/libc-top-half/musl/src/internal/lock.h
@@ -1,15 +1,50 @@
 #ifndef LOCK_H
 #define LOCK_H
 
-#if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
+// Defines internal locking primitives. The main elements defined here are:
+// - __lock_t: the type of a lock variable
+// - __lock_ptr_t: the type of a pointer to a lock variable
+// - __LOCK_INIT: initializer for a lock variable
+// - STRONG_LOCK/STRONG_UNLOCK: functions to acquire/release a lock for a critical section that contains 
+//                              potential context switch points, and thus must be executed even in cooperative threading mode.
+// - WEAK_LOCK/WEAK_UNLOCK: functions to acquire/release a lock for a critical section that does not contain any context switch points, 
+//                            and thus can be no-ops in cooperative threading mode.
+
+
+#ifdef __wasi_cooperative_threads__
+struct __waitlist_node;
+struct __coop_lock {
+	int owner;  // tid of owning thread, or 0 if unlocked
+	struct __waitlist_node *waiters;
+};
+
+typedef struct __coop_lock __lock_t;
+typedef struct __coop_lock *__lock_ptr_t;
+#define __COOP_LOCK_INIT {0, NULL}
+#define __LOCK_INIT __COOP_LOCK_INIT
+
+hidden void __lock(struct __coop_lock *lock);
+hidden void __unlock(struct __coop_lock *lock);
+#define STRONG_LOCK(x) __lock(x)
+#define STRONG_UNLOCK(x) __unlock(x)
+#define WEAK_LOCK(x) ((void)0)
+#define WEAK_UNLOCK(x) ((void)0)
+#elif defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
+typedef volatile int __lock_t;
+typedef volatile int *__lock_ptr_t;
+#define __LOCK_INIT {0}
 hidden void __lock(volatile int *);
 hidden void __unlock(volatile int *);
-#define LOCK(x) __lock(x)
-#define UNLOCK(x) __unlock(x)
+#define STRONG_LOCK(x) __lock(x)
+#define STRONG_UNLOCK(x) __unlock(x)
+#define WEAK_LOCK(x) __lock(x)
+#define WEAK_UNLOCK(x) __unlock(x)
 #else
 // No locking needed.
-#define LOCK(x) ((void)0)
-#define UNLOCK(x) ((void)0)
+#define STRONG_LOCK(x) ((void)0)
+#define STRONG_UNLOCK(x) ((void)0)
+#define WEAK_LOCK(x) ((void)0)
+#define WEAK_UNLOCK(x) ((void)0)
 #endif
 
-#endif
+#endif
\ No newline at end of file
diff --git a/libc-top-half/musl/src/internal/pthread_impl.h b/libc-top-half/musl/src/internal/pthread_impl.h
index 0106ac385..7a056d69d 100644
--- a/libc-top-half/musl/src/internal/pthread_impl.h
+++ b/libc-top-half/musl/src/internal/pthread_impl.h
@@ -18,6 +18,8 @@
 #include "futex.h"
 
 #include "pthread_arch.h"
+#include "lock.h"
+#include <wasi/version.h>
 
 #define pthread __pthread
 
@@ -172,35 +174,24 @@ hidden int __libc_sigaction(int, const struct sigaction *, struct sigaction *);
 #endif
 hidden void __unmapself(void *, size_t);
 
+#ifdef __wasi_cooperative_threads__
+struct __waitlist_node {
+    uint32_t tid;
+    struct __waitlist_node *next;
+};
+hidden void __waitlist_wait_on(struct __waitlist_node **list);
+hidden void __waitlist_wake_one(struct __waitlist_node **list);
+hidden void __waitlist_wake_all(struct __waitlist_node **list);
+#else
 #ifndef __wasilibc_unmodified_upstream
 hidden int __wasilibc_futex_wait(volatile void *, int, int, int64_t);
 #endif
 hidden int __timedwait(volatile int *, int, clockid_t, const struct timespec *, int);
 hidden int __timedwait_cp(volatile int *, int, clockid_t, const struct timespec *, int);
 hidden void __wait(volatile int *, volatile int *, int, int);
-static inline void __wake(volatile void *addr, int cnt, int priv)
-{
-	if (priv) priv = FUTEX_PRIVATE;
-	if (cnt<0) cnt = INT_MAX;
-#ifdef __wasilibc_unmodified_upstream
-	__syscall(SYS_futex, addr, FUTEX_WAKE|priv, cnt) != -ENOSYS ||
-	__syscall(SYS_futex, addr, FUTEX_WAKE, cnt);
-#else
-#ifdef _REENTRANT
-	__builtin_wasm_memory_atomic_notify((int*)addr, cnt);
-#endif
-#endif
-}
-static inline void __futexwait(volatile void *addr, int val, int priv)
-{
-#ifdef __wasilibc_unmodified_upstream
-	if (priv) priv = FUTEX_PRIVATE;
-	__syscall(SYS_futex, addr, FUTEX_WAIT|priv, val, 0) != -ENOSYS ||
-	__syscall(SYS_futex, addr, FUTEX_WAIT, val, 0);
-#else
-	__wait(addr, NULL, val, priv);
+hidden void __wake(volatile void *addr, int cnt, int priv);
+hidden void __futexwait(volatile void *addr, int val, int priv);
 #endif
-}
 
 hidden void __acquire_ptc(void);
 hidden void __release_ptc(void);
diff --git a/libc-top-half/musl/src/internal/stdio_impl.h b/libc-top-half/musl/src/internal/stdio_impl.h
index 7f19dd951..ce0e1bc2f 100644
--- a/libc-top-half/musl/src/internal/stdio_impl.h
+++ b/libc-top-half/musl/src/internal/stdio_impl.h
@@ -8,10 +8,20 @@
 
 #define UNGET 8
 
-#if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
+#include "lock.h"
+
+#ifdef __wasi_cooperative_threads__
+#define FFINALLOCK(f) __lockfile((f))
+#define FLOCK(f) int __need_unlock = __lockfile((f))
+#define FUNLOCK(f) do { if (__need_unlock) __unlockfile((f)); } while (0)
+#define __STDIO_LOCK_INIT {0, 0}
+#define __STDIO_LOCK_RESET(lock) do { (lock)->owner = 0; (lock)->waiters = NULL; } while (0)
+#elif defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
 #define FFINALLOCK(f) ((f)->lock>=0 ? __lockfile((f)) : 0)
 #define FLOCK(f) int __need_unlock = ((f)->lock>=0 ? __lockfile((f)) : 0)
 #define FUNLOCK(f) do { if (__need_unlock) __unlockfile((f)); } while (0)
+#define __STDIO_LOCK_INIT -1
+#define __STDIO_LOCK_RESET(lock) do { (*(lock)) = -1; } while (0)
 #else
 // No locking needed.
 #define FFINALLOCK(f) ((void)(f))
@@ -51,7 +61,7 @@ struct _IO_FILE {
 #endif
 	int mode;
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	volatile int lock;
+	__lock_t lock;
 #endif
 	int lbf;
 	void *cookie;
diff --git a/libc-top-half/musl/src/locale/locale_map.c b/libc-top-half/musl/src/locale/locale_map.c
index ebfb158f4..ca25ac827 100644
--- a/libc-top-half/musl/src/locale/locale_map.c
+++ b/libc-top-half/musl/src/locale/locale_map.c
@@ -31,8 +31,8 @@ static const char envvars[][12] = {
 };
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-volatile int __locale_lock[1];
-volatile int *const __locale_lockptr = __locale_lock;
+__lock_t __locale_lock[1];
+__lock_t *const __locale_lockptr = __locale_lock;
 #endif
 
 const struct __locale_map *__get_locale(int cat, const char *val)
diff --git a/libc-top-half/musl/src/locale/newlocale.c b/libc-top-half/musl/src/locale/newlocale.c
index 11c778557..814adab0e 100644
--- a/libc-top-half/musl/src/locale/newlocale.c
+++ b/libc-top-half/musl/src/locale/newlocale.c
@@ -63,9 +63,9 @@ static locale_t do_newlocale(int mask, const char *name, locale_t loc)
 
 locale_t __newlocale(int mask, const char *name, locale_t loc)
 {
-	LOCK(__locale_lock);
+	STRONG_LOCK(__locale_lock);
 	loc = do_newlocale(mask, name, loc);
-	UNLOCK(__locale_lock);
+	STRONG_UNLOCK(__locale_lock);
 	return loc;
 }
 
diff --git a/libc-top-half/musl/src/locale/setlocale.c b/libc-top-half/musl/src/locale/setlocale.c
index 360c44376..18f2a2c1e 100644
--- a/libc-top-half/musl/src/locale/setlocale.c
+++ b/libc-top-half/musl/src/locale/setlocale.c
@@ -13,7 +13,7 @@ char *setlocale(int cat, const char *name)
 
 	if ((unsigned)cat > LC_ALL) return 0;
 
-	LOCK(__locale_lock);
+	STRONG_LOCK(__locale_lock);
 
 	/* For LC_ALL, setlocale is required to return a string which
 	 * encodes the current setting for all categories. The format of
@@ -35,7 +35,7 @@ char *setlocale(int cat, const char *name)
 				}
 				lm = __get_locale(i, part);
 				if (lm == LOC_MAP_FAILED) {
-					UNLOCK(__locale_lock);
+					STRONG_UNLOCK(__locale_lock);
 					return 0;
 				}
 				tmp_locale.cat[i] = lm;
@@ -56,14 +56,14 @@ char *setlocale(int cat, const char *name)
 			s += l+1;
 		}
 		*--s = 0;
-		UNLOCK(__locale_lock);
+		STRONG_UNLOCK(__locale_lock);
 		return same==LC_ALL ? (char *)part : buf;
 	}
 
 	if (name) {
 		lm = __get_locale(cat, name);
 		if (lm == LOC_MAP_FAILED) {
-			UNLOCK(__locale_lock);
+			STRONG_UNLOCK(__locale_lock);
 			return 0;
 		}
 		libc.global_locale.cat[cat] = lm;
@@ -72,7 +72,7 @@ char *setlocale(int cat, const char *name)
 	}
 	char *ret = lm ? (char *)lm->name : "C";
 
-	UNLOCK(__locale_lock);
+	STRONG_UNLOCK(__locale_lock);
 
 	return ret;
 }
diff --git a/libc-top-half/musl/src/malloc/oldmalloc/malloc.c b/libc-top-half/musl/src/malloc/oldmalloc/malloc.c
index 25d00d44d..f4caed87c 100644
--- a/libc-top-half/musl/src/malloc/oldmalloc/malloc.c
+++ b/libc-top-half/musl/src/malloc/oldmalloc/malloc.c
@@ -27,6 +27,16 @@ static struct {
 
 /* Synchronization tools */
 
+#ifdef __wasi_cooperative_threads__
+/* The implementation has no yield points, so locks can be no-ops. */
+static inline void lock(volatile int *lk)
+{
+}
+
+static inline void unlock(volatile int *lk)
+{
+}
+#else
 static inline void lock(volatile int *lk)
 {
 	int need_locks = libc.need_locks;
@@ -43,6 +53,7 @@ static inline void unlock(volatile int *lk)
 		if (lk[1]) __wake(lk, 1, 1);
 	}
 }
+#endif
 
 static inline void lock_bin(int i)
 {
diff --git a/libc-top-half/musl/src/prng/random.c b/libc-top-half/musl/src/prng/random.c
index daac028d8..957f2f955 100644
--- a/libc-top-half/musl/src/prng/random.c
+++ b/libc-top-half/musl/src/prng/random.c
@@ -24,8 +24,8 @@ static int i = 3;
 static int j = 0;
 static uint32_t *x = init+1;
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-static volatile int lock[1];
-volatile int *const __random_lockptr = lock;
+static __lock_t lock[1];
+__lock_t *const __random_lockptr = lock;
 #endif
 
 static uint32_t lcg31(uint32_t x) {
@@ -67,9 +67,11 @@ static void __srandom(unsigned seed) {
 }
 
 void srandom(unsigned seed) {
-	LOCK(lock);
+	// The random number generator does not hit any context switch points, 
+	// so we can use weak locks here.
+	WEAK_LOCK(lock);
 	__srandom(seed);
-	UNLOCK(lock);
+	WEAK_UNLOCK(lock);
 }
 
 char *initstate(unsigned seed, char *state, size_t size) {
@@ -77,7 +79,7 @@ char *initstate(unsigned seed, char *state, size_t size) {
 
 	if (size < 8)
 		return 0;
-	LOCK(lock);
+	WEAK_LOCK(lock);
 	old = savestate();
 	if (size < 32)
 		n = 0;
@@ -92,24 +94,24 @@ char *initstate(unsigned seed, char *state, size_t size) {
 	x = (uint32_t*)state + 1;
 	__srandom(seed);
 	savestate();
-	UNLOCK(lock);
+	WEAK_UNLOCK(lock);
 	return old;
 }
 
 char *setstate(char *state) {
 	void *old;
 
-	LOCK(lock);
+	WEAK_LOCK(lock);
 	old = savestate();
 	loadstate((uint32_t*)state);
-	UNLOCK(lock);
+	WEAK_UNLOCK(lock);
 	return old;
 }
 
 long random(void) {
 	long k;
 
-	LOCK(lock);
+	WEAK_LOCK(lock);
 	if (n == 0) {
 		k = x[0] = lcg31(x[0]);
 		goto end;
@@ -121,6 +123,6 @@ long random(void) {
 	if (++j == n)
 		j = 0;
 end:
-	UNLOCK(lock);
+	WEAK_UNLOCK(lock);
 	return k;
 }
diff --git a/libc-top-half/musl/src/stdio/__fdopen.c b/libc-top-half/musl/src/stdio/__fdopen.c
index 5c8df495e..205338c2f 100644
--- a/libc-top-half/musl/src/stdio/__fdopen.c
+++ b/libc-top-half/musl/src/stdio/__fdopen.c
@@ -75,7 +75,7 @@ FILE *__fdopen(int fd, const char *mode)
 	f->close = __stdio_close;
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	if (!libc.threaded) f->lock = -1;
+	if (!libc.threaded) __STDIO_LOCK_RESET(&f->lock);
 #endif
 
 	/* Add new FILE to open file list */
diff --git a/libc-top-half/musl/src/stdio/__fopen_rb_ca.c b/libc-top-half/musl/src/stdio/__fopen_rb_ca.c
index 192050b00..27c2544fe 100644
--- a/libc-top-half/musl/src/stdio/__fopen_rb_ca.c
+++ b/libc-top-half/musl/src/stdio/__fopen_rb_ca.c
@@ -25,7 +25,7 @@ FILE *__fopen_rb_ca(const char *filename, FILE *f, unsigned char *buf, size_t le
 	f->seek = __stdio_seek;
 	f->close = __stdio_close;
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	f->lock = -1;
+	__STDIO_LOCK_RESET(&f->lock);
 #endif
 
 	return f;
diff --git a/libc-top-half/musl/src/stdio/__lockfile.c b/libc-top-half/musl/src/stdio/__lockfile.c
index 0f60a1499..206e46597 100644
--- a/libc-top-half/musl/src/stdio/__lockfile.c
+++ b/libc-top-half/musl/src/stdio/__lockfile.c
@@ -1,6 +1,29 @@
 #include "stdio_impl.h"
 #include "pthread_impl.h"
 
+#ifdef __wasi_cooperative_threads__
+#include "lock.h"
+int __lockfile(FILE *f)
+{
+	#ifdef __wasip3__
+	int tid = wasip3_thread_index();
+	#else
+	#error "Unknown WASI version"
+	#endif
+
+	// Allow recursive locking
+	if (f->lock.owner == tid)
+		return 0;
+
+	STRONG_LOCK(&f->lock);
+	return 1;
+}
+
+void __unlockfile(FILE *f)
+{
+	STRONG_UNLOCK(&f->lock);
+}
+#else
 int __lockfile(FILE *f)
 {
 	int owner = f->lock, tid = __pthread_self()->tid;
@@ -21,3 +44,4 @@ void __unlockfile(FILE *f)
 	if (a_swap(&f->lock, 0) & MAYBE_WAITERS)
 		__wake(&f->lock, 1, 1);
 }
+#endif
diff --git a/libc-top-half/musl/src/stdio/fmemopen.c b/libc-top-half/musl/src/stdio/fmemopen.c
index 3ee57b9ea..22628e56f 100644
--- a/libc-top-half/musl/src/stdio/fmemopen.c
+++ b/libc-top-half/musl/src/stdio/fmemopen.c
@@ -130,7 +130,7 @@ FILE *fmemopen(void *restrict buf, size_t size, const char *restrict mode)
 	f->f.close = mclose;
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	if (!libc.threaded) f->f.lock = -1;
+	if (!libc.threaded) __STDIO_LOCK_RESET(&f->f.lock);
 #endif
 
 	return __ofl_add(&f->f);
diff --git a/libc-top-half/musl/src/stdio/ftrylockfile.c b/libc-top-half/musl/src/stdio/ftrylockfile.c
index 50650585b..931214ffa 100644
--- a/libc-top-half/musl/src/stdio/ftrylockfile.c
+++ b/libc-top-half/musl/src/stdio/ftrylockfile.c
@@ -4,9 +4,15 @@
 
 void __do_orphaned_stdio_locks()
 {
-	FILE *f;
-	for (f=__pthread_self()->stdio_locks; f; f=f->next_locked)
-		a_store(&f->lock, 0x40000000);
+    FILE *f;
+    for (f=__pthread_self()->stdio_locks; f; f=f->next_locked) {
+		#ifdef __wasi_cooperative_threads__
+        f->lock.owner = 0;
+        __waitlist_wake_all(&f->lock.waiters);
+		#else
+        a_store(&f->lock, 0x40000000);
+		#endif
+    }
 }
 
 void __unlist_locked_file(FILE *f)
@@ -27,6 +33,31 @@ void __register_locked_file(FILE *f, pthread_t self)
 	self->stdio_locks = f;
 }
 
+#ifdef __wasi_cooperative_threads__
+int ftrylockfile(FILE *f)
+{
+	#ifdef __wasip3__
+	uint32_t self_tid = wasip3_thread_index();
+	#else
+	#error "Unknown WASI version"
+	#endif
+
+	if (f->lock.owner == self_tid) {
+		if (f->lockcount == LONG_MAX)
+			return -1;
+		f->lockcount++;
+		return 0;
+	}
+
+	// Try to acquire the lock
+	if (f->lock.owner != 0)
+		return -1;
+
+	f->lock.owner = self_tid;
+	f->lockcount = 1;
+	return 0;
+}
+#else
 int ftrylockfile(FILE *f)
 {
 	pthread_t self = __pthread_self();
@@ -44,3 +75,4 @@ int ftrylockfile(FILE *f)
 	__register_locked_file(f, self);
 	return 0;
 }
+#endif
diff --git a/libc-top-half/musl/src/stdio/getc.h b/libc-top-half/musl/src/stdio/getc.h
index e62e3f0da..7502102dc 100644
--- a/libc-top-half/musl/src/stdio/getc.h
+++ b/libc-top-half/musl/src/stdio/getc.h
@@ -7,17 +7,28 @@ __attribute__((__noinline__))
 #endif
 static int locking_getc(FILE *f)
 {
+#ifdef __wasi_cooperative_threads__
+    __lockfile(f);
+    int c = getc_unlocked(f);
+    __unlockfile(f);
+	return c;
+#else
 	if (a_cas(&f->lock, 0, MAYBE_WAITERS-1)) __lockfile(f);
 	int c = getc_unlocked(f);
 	if (a_swap(&f->lock, 0) & MAYBE_WAITERS)
 		__wake(&f->lock, 1, 1);
 	return c;
+#endif
 }
 #endif
 
 static inline int do_getc(FILE *f)
 {
-#if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
+#ifdef __wasi_cooperative_threads__
+	if (f->lock.owner == wasip3_thread_index())
+		return getc_unlocked(f);
+	return locking_getc(f);
+#elif defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
 	int l = f->lock;
 	if (l < 0 || l && (l & ~MAYBE_WAITERS) == __pthread_self()->tid)
 		return getc_unlocked(f);
diff --git a/libc-top-half/musl/src/stdio/ofl.c b/libc-top-half/musl/src/stdio/ofl.c
index 33a8aa50b..2a298a2f8 100644
--- a/libc-top-half/musl/src/stdio/ofl.c
+++ b/libc-top-half/musl/src/stdio/ofl.c
@@ -4,17 +4,17 @@
 
 static FILE *ofl_head;
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-static volatile int ofl_lock[1];
-volatile int *const __stdio_ofl_lockptr = ofl_lock;
+static __lock_t ofl_lock[1];
+__lock_t *const __stdio_ofl_lockptr = ofl_lock;
 #endif
 
 FILE **__ofl_lock()
 {
-	LOCK(ofl_lock);
+	STRONG_LOCK(ofl_lock);
 	return &ofl_head;
 }
 
 void __ofl_unlock()
 {
-	UNLOCK(ofl_lock);
+	STRONG_UNLOCK(ofl_lock);
 }
diff --git a/libc-top-half/musl/src/stdio/open_memstream.c b/libc-top-half/musl/src/stdio/open_memstream.c
index aa5022065..9690fe8b3 100644
--- a/libc-top-half/musl/src/stdio/open_memstream.c
+++ b/libc-top-half/musl/src/stdio/open_memstream.c
@@ -102,7 +102,7 @@ FILE *open_memstream(char **bufp, size_t *sizep)
 	f->f.mode = -1;
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	if (!libc.threaded) f->f.lock = -1;
+	if (!libc.threaded) __STDIO_LOCK_RESET(&f->f.lock);
 #endif
 
 	return __ofl_add(&f->f);
diff --git a/libc-top-half/musl/src/stdio/open_wmemstream.c b/libc-top-half/musl/src/stdio/open_wmemstream.c
index 198d5d439..d06c24db8 100644
--- a/libc-top-half/musl/src/stdio/open_wmemstream.c
+++ b/libc-top-half/musl/src/stdio/open_wmemstream.c
@@ -107,7 +107,7 @@ FILE *open_wmemstream(wchar_t **bufp, size_t *sizep)
 	f->f.close = wms_close;
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	if (!libc.threaded) f->f.lock = -1;
+	if (!libc.threaded) __STDIO_LOCK_RESET(&f->f.lock);
 #endif
 
 	fwide(&f->f, 1);
diff --git a/libc-top-half/musl/src/stdio/putc.h b/libc-top-half/musl/src/stdio/putc.h
index 2cc63d2db..aae780ab3 100644
--- a/libc-top-half/musl/src/stdio/putc.h
+++ b/libc-top-half/musl/src/stdio/putc.h
@@ -7,17 +7,33 @@ __attribute__((__noinline__))
 #endif
 static int locking_putc(int c, FILE *f)
 {
+#ifdef __wasi_cooperative_threads__
+	__lockfile(f);
+	c = putc_unlocked(c, f);
+	__unlockfile(f);
+	return c;
+#else
 	if (a_cas(&f->lock, 0, MAYBE_WAITERS-1)) __lockfile(f);
 	c = putc_unlocked(c, f);
 	if (a_swap(&f->lock, 0) & MAYBE_WAITERS)
 		__wake(&f->lock, 1, 1);
 	return c;
+#endif
 }
 #endif
 
 static inline int do_putc(int c, FILE *f)
 {
-#if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
+#ifdef __wasi_cooperative_threads__
+	#ifdef __wasip3__
+	int tid = wasip3_thread_index();
+	#else
+	#error "Unknown WASI version"
+	#endif
+	if (f->lock.owner == tid)
+		return putc_unlocked(c, f);
+	return locking_putc(c, f);
+#elif defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
 	int l = f->lock;
 	if (l < 0 || l && (l & ~MAYBE_WAITERS) == __pthread_self()->tid)
 		return putc_unlocked(c, f);
diff --git a/libc-top-half/musl/src/stdio/stderr.c b/libc-top-half/musl/src/stdio/stderr.c
index 5f24549f8..a14ba5637 100644
--- a/libc-top-half/musl/src/stdio/stderr.c
+++ b/libc-top-half/musl/src/stdio/stderr.c
@@ -13,7 +13,7 @@ hidden FILE __stderr_FILE = {
 	.seek = __stdio_seek,
 	.close = __stdio_close,
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	.lock = -1,
+	.lock = __STDIO_LOCK_INIT,
 #endif
 };
 FILE *const stderr = &__stderr_FILE;
diff --git a/libc-top-half/musl/src/stdio/stdin.c b/libc-top-half/musl/src/stdio/stdin.c
index 68e1c3f64..ddc1a892a 100644
--- a/libc-top-half/musl/src/stdio/stdin.c
+++ b/libc-top-half/musl/src/stdio/stdin.c
@@ -12,7 +12,7 @@ hidden FILE __stdin_FILE = {
 	.seek = __stdio_seek,
 	.close = __stdio_close,
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	.lock = -1,
+	.lock = __STDIO_LOCK_INIT,
 #endif
 };
 FILE *const stdin = &__stdin_FILE;
diff --git a/libc-top-half/musl/src/stdio/stdout.c b/libc-top-half/musl/src/stdio/stdout.c
index e0e2bced9..914f5a456 100644
--- a/libc-top-half/musl/src/stdio/stdout.c
+++ b/libc-top-half/musl/src/stdio/stdout.c
@@ -13,7 +13,7 @@ hidden FILE __stdout_FILE = {
 	.seek = __stdio_seek,
 	.close = __stdio_close,
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	.lock = -1,
+	.lock = __STDIO_LOCK_INIT,
 #endif
 };
 FILE *const stdout = &__stdout_FILE;
diff --git a/libc-top-half/musl/src/stdio/vdprintf.c b/libc-top-half/musl/src/stdio/vdprintf.c
index cef0a1af2..4ab32308a 100644
--- a/libc-top-half/musl/src/stdio/vdprintf.c
+++ b/libc-top-half/musl/src/stdio/vdprintf.c
@@ -6,7 +6,7 @@ int vdprintf(int fd, const char *restrict fmt, va_list ap)
 		.fd = fd, .lbf = EOF, .write = __stdio_write,
 		.buf = (void *)fmt, .buf_size = 0,
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-		.lock = -1
+		.lock = __STDIO_LOCK_INIT,
 #endif
 	};
 	return vfprintf(&f, fmt, ap);
diff --git a/libc-top-half/musl/src/stdio/vsscanf.c b/libc-top-half/musl/src/stdio/vsscanf.c
index 0e5b48265..883e1d8c4 100644
--- a/libc-top-half/musl/src/stdio/vsscanf.c
+++ b/libc-top-half/musl/src/stdio/vsscanf.c
@@ -19,10 +19,9 @@ int vsscanf(const char *restrict s, const char *restrict fmt, va_list ap)
 {
 	FILE f = {
 		.buf = (void *)s, .cookie = (void *)s,
+		.read = string_read,
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-		.read = string_read, .lock = -1
-#else
-		.read = string_read
+		.lock = __STDIO_LOCK_INIT
 #endif
 	};
 	return vfscanf(&f, fmt, ap);
diff --git a/libc-top-half/musl/src/stdio/vswscanf.c b/libc-top-half/musl/src/stdio/vswscanf.c
index ea827102d..feef4e451 100644
--- a/libc-top-half/musl/src/stdio/vswscanf.c
+++ b/libc-top-half/musl/src/stdio/vswscanf.c
@@ -30,10 +30,9 @@ int vswscanf(const wchar_t *restrict s, const wchar_t *restrict fmt, va_list ap)
 	FILE f = {
 		.buf = buf, .buf_size = sizeof buf,
 		.cookie = (void *)s,
+		.read = wstring_read,
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-		.read = wstring_read, .lock = -1
-#else
-		.read = wstring_read
+		.lock = __STDIO_LOCK_INIT
 #endif
 	};
 	return vfwscanf(&f, fmt, ap);
diff --git a/libc-top-half/musl/src/stdlib/wcstod.c b/libc-top-half/musl/src/stdlib/wcstod.c
index 97b894eb2..c198f08c5 100644
--- a/libc-top-half/musl/src/stdlib/wcstod.c
+++ b/libc-top-half/musl/src/stdlib/wcstod.c
@@ -44,7 +44,7 @@ static long double wcstox(const wchar_t *s, wchar_t **p, int prec)
 	f.rpos = f.rend = f.buf = buf + 4;
 	f.buf_size = sizeof buf - 4;
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	f.lock = -1;
+	__STDIO_LOCK_RESET(&f.lock);
 #endif
 	f.read = do_read;
 	while (iswspace(*t)) t++;
diff --git a/libc-top-half/musl/src/stdlib/wcstol.c b/libc-top-half/musl/src/stdlib/wcstol.c
index 3aefd06f4..43439c0d0 100644
--- a/libc-top-half/musl/src/stdlib/wcstol.c
+++ b/libc-top-half/musl/src/stdlib/wcstol.c
@@ -38,7 +38,7 @@ static unsigned long long wcstox(const wchar_t *s, wchar_t **p, int base, unsign
 	f.rpos = f.rend = f.buf = buf + 4;
 	f.buf_size = sizeof buf - 4;
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-	f.lock = -1;
+	__STDIO_LOCK_RESET(&f.lock);
 #endif
 	f.read = do_read;
 	while (iswspace(*t)) t++;
diff --git a/libc-top-half/musl/src/thread/coop-threads/__lock.c b/libc-top-half/musl/src/thread/coop-threads/__lock.c
new file mode 100644
index 000000000..9baeceff0
--- /dev/null
+++ b/libc-top-half/musl/src/thread/coop-threads/__lock.c
@@ -0,0 +1,38 @@
+#include "pthread_impl.h"
+#include "lock.h"
+#include <wasi/api.h>
+
+#ifndef __wasip3__
+#error "Unknown WASI version"
+#endif
+
+void __lock(struct __coop_lock *lock)
+{
+	int tid = wasip3_thread_index();
+	if (lock->owner == tid) {
+		/* Trap on recursive locking. */
+		__builtin_trap();
+	}
+
+	/* Loop until we acquire the lock. */
+	while (lock->owner != 0) {
+		__waitlist_wait_on(&lock->waiters);
+		/* After waking, the lock might still be held by another
+		 * thread that was scheduled before us, so loop back. */
+	}
+	
+	lock->owner = tid;
+}
+
+void __unlock(struct __coop_lock *lock)
+{
+	int tid = wasip3_thread_index();
+	if (lock->owner != tid) {
+		/* We're trying to unlock a lock we don't own. */
+		__builtin_trap();
+	}
+
+	lock->owner = 0;
+	/* Awake one waiter; the others will be resumed on future unlocks. */ 
+	__waitlist_wake_one(&lock->waiters);
+}
\ No newline at end of file
diff --git a/libc-top-half/musl/src/thread/coop-threads/__wait.c b/libc-top-half/musl/src/thread/coop-threads/__wait.c
new file mode 100644
index 000000000..1ccae74a5
--- /dev/null
+++ b/libc-top-half/musl/src/thread/coop-threads/__wait.c
@@ -0,0 +1,47 @@
+#include "pthread_impl.h"
+#include <wasi/api.h>
+
+#ifndef __wasip3__
+#error "Unknown WASI version"
+#endif
+
+void __waitlist_wait_on(struct __waitlist_node **list)
+{
+    struct __waitlist_node node = {
+        .tid = wasip3_thread_index(),
+        .next = *list,
+    };
+    *list = &node;
+    
+    wasip3_thread_suspend();
+}
+
+void __waitlist_wake_one(struct __waitlist_node **list)
+{
+    if (*list == NULL) {
+        return;
+    }
+    struct __waitlist_node *node = *list;
+    *list = node->next;
+    wasip3_thread_yield_to_suspended(node->tid);
+}
+
+void __waitlist_wake_all(struct __waitlist_node **list)
+{
+    struct __waitlist_node **prev = list;
+    struct __waitlist_node *curr = *list;
+
+    while (curr) {
+        uint32_t tid = curr->tid;
+        *prev = curr->next;
+        // As a scheduling optimization, we always yield directly to the last
+        // suspended thread instead of just scheduling it to run at some point.
+        if (curr->next == NULL) {
+            wasip3_thread_yield_to_suspended(tid);
+        }
+        else {
+            wasip3_thread_unsuspend(tid);
+        }
+        curr = *prev;
+    }
+}
\ No newline at end of file

From 36a0eed691a1a0ad4848221d37b55f7d614be41b Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 19:27:23 +0000
Subject: [PATCH 05/28] Cleanup

---
 CMakeLists.txt                                         |  3 +++
 .../cloudlibc/src/libc/sched/sched_yield.c             |  1 -
 libc-top-half/CMakeLists.txt                           |  9 +++++++++
 libc-top-half/musl/src/env/__init_tls.c                | 10 +++++++++-
 libc-top-half/musl/src/internal/lock.h                 |  2 ++
 libc-top-half/musl/src/internal/stdio_impl.h           |  1 +
 libc-top-half/musl/src/stdio/__lockfile.c              |  8 +-------
 libc-top-half/musl/src/stdio/ftrylockfile.c            |  7 +------
 libc-top-half/musl/src/stdio/getc.h                    |  3 ++-
 libc-top-half/musl/src/stdio/putc.h                    |  8 ++------
 libc-top-half/musl/src/thread/coop-threads/__lock.c    |  7 +++----
 libc-top-half/musl/src/thread/coop-threads/__wait.c    |  2 +-
 12 files changed, 34 insertions(+), 27 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 86793fdc8..5e261d183 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -87,6 +87,9 @@ endif()
 if(TARGET_TRIPLE MATCHES "-threads$")
   set(THREADS ON)
   add_compile_options(-mthread-model posix -pthread -ftls-model=local-exec -matomics)
+elseif(TARGET_TRIPLE MATCHES "-wasip3$")
+  set(THREADS OFF)
+  add_compile_options(-mthread-model posix -pthread -ftls-model=local-exec)
 else()
   set(THREADS OFF)
   add_compile_options(-mthread-model single)
diff --git a/libc-bottom-half/cloudlibc/src/libc/sched/sched_yield.c b/libc-bottom-half/cloudlibc/src/libc/sched/sched_yield.c
index c4b298e33..ceb0c9d43 100644
--- a/libc-bottom-half/cloudlibc/src/libc/sched/sched_yield.c
+++ b/libc-bottom-half/cloudlibc/src/libc/sched/sched_yield.c
@@ -15,7 +15,6 @@ int sched_yield(void) {
     #error "Unknown WASI version"
   #endif
 #elif defined(__wasip1__)
-#ifdef __wasip1__
   __wasi_errno_t error = __wasi_sched_yield();
   if (error != 0) {
     errno = error;
diff --git a/libc-top-half/CMakeLists.txt b/libc-top-half/CMakeLists.txt
index 69f758eb6..4777ba5d6 100644
--- a/libc-top-half/CMakeLists.txt
+++ b/libc-top-half/CMakeLists.txt
@@ -473,6 +473,15 @@ else()
   )
 endif()
 
+# Cooperative threading lock/waiting primitives
+if (WASI STREQUAL "p3")
+  list(APPEND top_half_sources
+    musl/src/stdio/__lockfile.c
+    musl/src/thread/coop-threads/__lock.c
+    musl/src/thread/coop-threads/__wait.c
+  )
+endif()
+
 add_object_library(top-half ${top_half_sources})
 foreach(obj top-half-shared top-half-static)
   target_link_libraries(${obj} PUBLIC musl-top-half-interface)
diff --git a/libc-top-half/musl/src/env/__init_tls.c b/libc-top-half/musl/src/env/__init_tls.c
index 7f0d92931..c37507749 100644
--- a/libc-top-half/musl/src/env/__init_tls.c
+++ b/libc-top-half/musl/src/env/__init_tls.c
@@ -12,6 +12,7 @@
 #include "libc.h"
 #include "atomic.h"
 #include "syscall.h"
+#include <wasi/api.h>
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
 volatile int __thread_list_lock;
@@ -97,7 +98,14 @@ int __init_tp(void *p)
 	td->stack = bounds.base;
 	td->stack_size = bounds.size;
 	td->guard_size = 0;
-#ifdef _REENTRANT
+#ifdef __wasi_cooperative_threads__
+	td->detach_state = DT_JOINABLE;
+	#ifdef __wasip3__
+	td->tid = wasip3_thread_index();
+	#else
+	#error "Unknown WASI version"
+	#endif
+#elif defined(_REENTRANT)
 	td->detach_state = DT_JOINABLE;
 	/*
 	 * Initialize the TID to a value which doesn't conflict with
diff --git a/libc-top-half/musl/src/internal/lock.h b/libc-top-half/musl/src/internal/lock.h
index 3e5a0a603..34503a002 100644
--- a/libc-top-half/musl/src/internal/lock.h
+++ b/libc-top-half/musl/src/internal/lock.h
@@ -1,6 +1,8 @@
 #ifndef LOCK_H
 #define LOCK_H
 
+#include <wasi/version.h>
+
 // Defines internal locking primitives. The main elements defined here are:
 // - __lock_t: the type of a lock variable
 // - __lock_ptr_t: the type of a pointer to a lock variable
diff --git a/libc-top-half/musl/src/internal/stdio_impl.h b/libc-top-half/musl/src/internal/stdio_impl.h
index ce0e1bc2f..7ea811393 100644
--- a/libc-top-half/musl/src/internal/stdio_impl.h
+++ b/libc-top-half/musl/src/internal/stdio_impl.h
@@ -9,6 +9,7 @@
 #define UNGET 8
 
 #include "lock.h"
+#include <wasi/version.h>
 
 #ifdef __wasi_cooperative_threads__
 #define FFINALLOCK(f) __lockfile((f))
diff --git a/libc-top-half/musl/src/stdio/__lockfile.c b/libc-top-half/musl/src/stdio/__lockfile.c
index 206e46597..042742547 100644
--- a/libc-top-half/musl/src/stdio/__lockfile.c
+++ b/libc-top-half/musl/src/stdio/__lockfile.c
@@ -5,14 +5,8 @@
 #include "lock.h"
 int __lockfile(FILE *f)
 {
-	#ifdef __wasip3__
-	int tid = wasip3_thread_index();
-	#else
-	#error "Unknown WASI version"
-	#endif
-
 	// Allow recursive locking
-	if (f->lock.owner == tid)
+	if (f->lock.owner == __pthread_self()->tid)
 		return 0;
 
 	STRONG_LOCK(&f->lock);
diff --git a/libc-top-half/musl/src/stdio/ftrylockfile.c b/libc-top-half/musl/src/stdio/ftrylockfile.c
index 931214ffa..489d46f88 100644
--- a/libc-top-half/musl/src/stdio/ftrylockfile.c
+++ b/libc-top-half/musl/src/stdio/ftrylockfile.c
@@ -36,12 +36,7 @@ void __register_locked_file(FILE *f, pthread_t self)
 #ifdef __wasi_cooperative_threads__
 int ftrylockfile(FILE *f)
 {
-	#ifdef __wasip3__
-	uint32_t self_tid = wasip3_thread_index();
-	#else
-	#error "Unknown WASI version"
-	#endif
-
+	int self_tid = __pthread_self()->tid;
 	if (f->lock.owner == self_tid) {
 		if (f->lockcount == LONG_MAX)
 			return -1;
diff --git a/libc-top-half/musl/src/stdio/getc.h b/libc-top-half/musl/src/stdio/getc.h
index 7502102dc..61074d607 100644
--- a/libc-top-half/musl/src/stdio/getc.h
+++ b/libc-top-half/musl/src/stdio/getc.h
@@ -1,6 +1,7 @@
 #include "stdio_impl.h"
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
 #include "pthread_impl.h"
+#include <wasi/api.h>
 
 #ifdef __GNUC__
 __attribute__((__noinline__))
@@ -25,7 +26,7 @@ static int locking_getc(FILE *f)
 static inline int do_getc(FILE *f)
 {
 #ifdef __wasi_cooperative_threads__
-	if (f->lock.owner == wasip3_thread_index())
+	if (f->lock.owner == __pthread_self()->tid)
 		return getc_unlocked(f);
 	return locking_getc(f);
 #elif defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
diff --git a/libc-top-half/musl/src/stdio/putc.h b/libc-top-half/musl/src/stdio/putc.h
index aae780ab3..7e1d49d6b 100644
--- a/libc-top-half/musl/src/stdio/putc.h
+++ b/libc-top-half/musl/src/stdio/putc.h
@@ -1,6 +1,7 @@
 #include "stdio_impl.h"
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
 #include "pthread_impl.h"
+#include <wasi/api.h>
 
 #ifdef __GNUC__
 __attribute__((__noinline__))
@@ -25,12 +26,7 @@ static int locking_putc(int c, FILE *f)
 static inline int do_putc(int c, FILE *f)
 {
 #ifdef __wasi_cooperative_threads__
-	#ifdef __wasip3__
-	int tid = wasip3_thread_index();
-	#else
-	#error "Unknown WASI version"
-	#endif
-	if (f->lock.owner == tid)
+	if (f->lock.owner == __pthread_self()->tid)
 		return putc_unlocked(c, f);
 	return locking_putc(c, f);
 #elif defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
diff --git a/libc-top-half/musl/src/thread/coop-threads/__lock.c b/libc-top-half/musl/src/thread/coop-threads/__lock.c
index 9baeceff0..939d87ad9 100644
--- a/libc-top-half/musl/src/thread/coop-threads/__lock.c
+++ b/libc-top-half/musl/src/thread/coop-threads/__lock.c
@@ -8,8 +8,7 @@
 
 void __lock(struct __coop_lock *lock)
 {
-	int tid = wasip3_thread_index();
-	if (lock->owner == tid) {
+	if (lock->owner == __pthread_self()->tid) {
 		/* Trap on recursive locking. */
 		__builtin_trap();
 	}
@@ -21,12 +20,12 @@ void __lock(struct __coop_lock *lock)
 		 * thread that was scheduled before us, so loop back. */
 	}
 	
-	lock->owner = tid;
+	lock->owner = __pthread_self()->tid;
 }
 
 void __unlock(struct __coop_lock *lock)
 {
-	int tid = wasip3_thread_index();
+	int tid = __pthread_self()->tid;
 	if (lock->owner != tid) {
 		/* We're trying to unlock a lock we don't own. */
 		__builtin_trap();
diff --git a/libc-top-half/musl/src/thread/coop-threads/__wait.c b/libc-top-half/musl/src/thread/coop-threads/__wait.c
index 1ccae74a5..db8646dcc 100644
--- a/libc-top-half/musl/src/thread/coop-threads/__wait.c
+++ b/libc-top-half/musl/src/thread/coop-threads/__wait.c
@@ -8,7 +8,7 @@
 void __waitlist_wait_on(struct __waitlist_node **list)
 {
     struct __waitlist_node node = {
-        .tid = wasip3_thread_index(),
+        .tid = __pthread_self()->tid,
         .next = *list,
     };
     *list = &node;

From 6e8568b5690e2cac90c100c2e17846dfd6ab434b Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 19:31:51 +0000
Subject: [PATCH 06/28] Formatting

---
 libc-top-half/musl/src/internal/lock.h | 64 ++++++++++++++------------
 1 file changed, 34 insertions(+), 30 deletions(-)

diff --git a/libc-top-half/musl/src/internal/lock.h b/libc-top-half/musl/src/internal/lock.h
index 34503a002..75d405524 100644
--- a/libc-top-half/musl/src/internal/lock.h
+++ b/libc-top-half/musl/src/internal/lock.h
@@ -14,39 +14,43 @@
 
 
 #ifdef __wasi_cooperative_threads__
-struct __waitlist_node;
-struct __coop_lock {
-	int owner;  // tid of owning thread, or 0 if unlocked
-	struct __waitlist_node *waiters;
-};
+    struct __waitlist_node;
+    struct __coop_lock {
+    	int owner;  // tid of owning thread, or 0 if unlocked
+    	struct __waitlist_node *waiters;
+    };
+    
+    typedef struct __coop_lock __lock_t;
+    typedef struct __coop_lock *__lock_ptr_t;
+    #define __COOP_LOCK_INIT {0, NULL}
+    #define __LOCK_INIT __COOP_LOCK_INIT
+    
+    hidden void __lock(struct __coop_lock *lock);
+    hidden void __unlock(struct __coop_lock *lock);
 
-typedef struct __coop_lock __lock_t;
-typedef struct __coop_lock *__lock_ptr_t;
-#define __COOP_LOCK_INIT {0, NULL}
-#define __LOCK_INIT __COOP_LOCK_INIT
-
-hidden void __lock(struct __coop_lock *lock);
-hidden void __unlock(struct __coop_lock *lock);
-#define STRONG_LOCK(x) __lock(x)
-#define STRONG_UNLOCK(x) __unlock(x)
-#define WEAK_LOCK(x) ((void)0)
-#define WEAK_UNLOCK(x) ((void)0)
+    #define STRONG_LOCK(x) __lock(x)
+    #define STRONG_UNLOCK(x) __unlock(x)
+    #define WEAK_LOCK(x) ((void)0)
+    #define WEAK_UNLOCK(x) ((void)0)
 #elif defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-typedef volatile int __lock_t;
-typedef volatile int *__lock_ptr_t;
-#define __LOCK_INIT {0}
-hidden void __lock(volatile int *);
-hidden void __unlock(volatile int *);
-#define STRONG_LOCK(x) __lock(x)
-#define STRONG_UNLOCK(x) __unlock(x)
-#define WEAK_LOCK(x) __lock(x)
-#define WEAK_UNLOCK(x) __unlock(x)
+    typedef volatile int __lock_t;
+    typedef volatile int *__lock_ptr_t;
+
+    #define __LOCK_INIT {0}
+    
+    hidden void __lock(volatile int *);
+    hidden void __unlock(volatile int *);
+    
+    #define STRONG_LOCK(x) __lock(x)
+    #define STRONG_UNLOCK(x) __unlock(x)
+    #define WEAK_LOCK(x) __lock(x)
+    #define WEAK_UNLOCK(x) __unlock(x)
 #else
-// No locking needed.
-#define STRONG_LOCK(x) ((void)0)
-#define STRONG_UNLOCK(x) ((void)0)
-#define WEAK_LOCK(x) ((void)0)
-#define WEAK_UNLOCK(x) ((void)0)
+    // No locking needed.
+    #define STRONG_LOCK(x) ((void)0)
+    #define STRONG_UNLOCK(x) ((void)0)
+    #define WEAK_LOCK(x) ((void)0)
+    #define WEAK_UNLOCK(x) ((void)0)
 #endif
 
 #endif
\ No newline at end of file

From ac451090c2d404b3a2b6aed589cb090c8732977d Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 20:19:38 +0000
Subject: [PATCH 07/28] Rename STRONG_LOCK

---
 libc-top-half/musl/src/internal/lock.h    | 16 ++++++++--------
 libc-top-half/musl/src/locale/newlocale.c |  4 ++--
 libc-top-half/musl/src/locale/setlocale.c | 10 +++++-----
 libc-top-half/musl/src/stdio/__lockfile.c |  4 ++--
 libc-top-half/musl/src/stdio/ofl.c        |  4 ++--
 5 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/libc-top-half/musl/src/internal/lock.h b/libc-top-half/musl/src/internal/lock.h
index 75d405524..feacd7ce8 100644
--- a/libc-top-half/musl/src/internal/lock.h
+++ b/libc-top-half/musl/src/internal/lock.h
@@ -7,8 +7,8 @@
 // - __lock_t: the type of a lock variable
 // - __lock_ptr_t: the type of a pointer to a lock variable
 // - __LOCK_INIT: initializer for a lock variable
-// - STRONG_LOCK/STRONG_UNLOCK: functions to acquire/release a lock for a critical section that contains 
-//                              potential context switch points, and thus must be executed even in cooperative threading mode.
+// - LOCK/UNLOCK: functions to acquire/release a lock for a critical section that contains 
+//                potential context switch points, and thus must be executed even in cooperative threading mode.
 // - WEAK_LOCK/WEAK_UNLOCK: functions to acquire/release a lock for a critical section that does not contain any context switch points, 
 //                            and thus can be no-ops in cooperative threading mode.
 
@@ -28,8 +28,8 @@
     hidden void __lock(struct __coop_lock *lock);
     hidden void __unlock(struct __coop_lock *lock);
 
-    #define STRONG_LOCK(x) __lock(x)
-    #define STRONG_UNLOCK(x) __unlock(x)
+    #define LOCK(x) __lock(x)
+    #define UNLOCK(x) __unlock(x)
     #define WEAK_LOCK(x) ((void)0)
     #define WEAK_UNLOCK(x) ((void)0)
 #elif defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
@@ -41,14 +41,14 @@
     hidden void __lock(volatile int *);
     hidden void __unlock(volatile int *);
     
-    #define STRONG_LOCK(x) __lock(x)
-    #define STRONG_UNLOCK(x) __unlock(x)
+    #define LOCK(x) __lock(x)
+    #define UNLOCK(x) __unlock(x)
     #define WEAK_LOCK(x) __lock(x)
     #define WEAK_UNLOCK(x) __unlock(x)
 #else
     // No locking needed.
-    #define STRONG_LOCK(x) ((void)0)
-    #define STRONG_UNLOCK(x) ((void)0)
+    #define LOCK(x) ((void)0)
+    #define UNLOCK(x) ((void)0)
     #define WEAK_LOCK(x) ((void)0)
     #define WEAK_UNLOCK(x) ((void)0)
 #endif
diff --git a/libc-top-half/musl/src/locale/newlocale.c b/libc-top-half/musl/src/locale/newlocale.c
index 814adab0e..11c778557 100644
--- a/libc-top-half/musl/src/locale/newlocale.c
+++ b/libc-top-half/musl/src/locale/newlocale.c
@@ -63,9 +63,9 @@ static locale_t do_newlocale(int mask, const char *name, locale_t loc)
 
 locale_t __newlocale(int mask, const char *name, locale_t loc)
 {
-	STRONG_LOCK(__locale_lock);
+	LOCK(__locale_lock);
 	loc = do_newlocale(mask, name, loc);
-	STRONG_UNLOCK(__locale_lock);
+	UNLOCK(__locale_lock);
 	return loc;
 }
 
diff --git a/libc-top-half/musl/src/locale/setlocale.c b/libc-top-half/musl/src/locale/setlocale.c
index 18f2a2c1e..360c44376 100644
--- a/libc-top-half/musl/src/locale/setlocale.c
+++ b/libc-top-half/musl/src/locale/setlocale.c
@@ -13,7 +13,7 @@ char *setlocale(int cat, const char *name)
 
 	if ((unsigned)cat > LC_ALL) return 0;
 
-	STRONG_LOCK(__locale_lock);
+	LOCK(__locale_lock);
 
 	/* For LC_ALL, setlocale is required to return a string which
 	 * encodes the current setting for all categories. The format of
@@ -35,7 +35,7 @@ char *setlocale(int cat, const char *name)
 				}
 				lm = __get_locale(i, part);
 				if (lm == LOC_MAP_FAILED) {
-					STRONG_UNLOCK(__locale_lock);
+					UNLOCK(__locale_lock);
 					return 0;
 				}
 				tmp_locale.cat[i] = lm;
@@ -56,14 +56,14 @@ char *setlocale(int cat, const char *name)
 			s += l+1;
 		}
 		*--s = 0;
-		STRONG_UNLOCK(__locale_lock);
+		UNLOCK(__locale_lock);
 		return same==LC_ALL ? (char *)part : buf;
 	}
 
 	if (name) {
 		lm = __get_locale(cat, name);
 		if (lm == LOC_MAP_FAILED) {
-			STRONG_UNLOCK(__locale_lock);
+			UNLOCK(__locale_lock);
 			return 0;
 		}
 		libc.global_locale.cat[cat] = lm;
@@ -72,7 +72,7 @@ char *setlocale(int cat, const char *name)
 	}
 	char *ret = lm ? (char *)lm->name : "C";
 
-	STRONG_UNLOCK(__locale_lock);
+	UNLOCK(__locale_lock);
 
 	return ret;
 }
diff --git a/libc-top-half/musl/src/stdio/__lockfile.c b/libc-top-half/musl/src/stdio/__lockfile.c
index 042742547..77878783a 100644
--- a/libc-top-half/musl/src/stdio/__lockfile.c
+++ b/libc-top-half/musl/src/stdio/__lockfile.c
@@ -9,13 +9,13 @@ int __lockfile(FILE *f)
 	if (f->lock.owner == __pthread_self()->tid)
 		return 0;
 
-	STRONG_LOCK(&f->lock);
+	LOCK(&f->lock);
 	return 1;
 }
 
 void __unlockfile(FILE *f)
 {
-	STRONG_UNLOCK(&f->lock);
+	UNLOCK(&f->lock);
 }
 #else
 int __lockfile(FILE *f)
diff --git a/libc-top-half/musl/src/stdio/ofl.c b/libc-top-half/musl/src/stdio/ofl.c
index 2a298a2f8..d69ee2805 100644
--- a/libc-top-half/musl/src/stdio/ofl.c
+++ b/libc-top-half/musl/src/stdio/ofl.c
@@ -10,11 +10,11 @@ __lock_t *const __stdio_ofl_lockptr = ofl_lock;
 
 FILE **__ofl_lock()
 {
-	STRONG_LOCK(ofl_lock);
+	LOCK(ofl_lock);
 	return &ofl_head;
 }
 
 void __ofl_unlock()
 {
-	STRONG_UNLOCK(ofl_lock);
+	UNLOCK(ofl_lock);
 }

From 1f67537f4ab8a5c0268a744f2597018166af4bbe Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 20:21:50 +0000
Subject: [PATCH 08/28] Rename STRONG_LOCK

---
 libc-bottom-half/sources/preopens.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/libc-bottom-half/sources/preopens.c b/libc-bottom-half/sources/preopens.c
index 84738c53f..077c12318 100644
--- a/libc-bottom-half/sources/preopens.c
+++ b/libc-bottom-half/sources/preopens.c
@@ -220,11 +220,11 @@ static bool prefix_matches(const char *prefix, size_t prefix_len,
 /// This function takes ownership of `prefix`.
 static int internal_register_preopened_fd(__wasi_fd_t fd,
                                           const char *relprefix) {
-  STRONG_LOCK(lock);
+  LOCK(lock);
 
   int r = internal_register_preopened_fd_unlocked(fd, relprefix);
 
-  STRONG_UNLOCK(lock);
+  UNLOCK(lock);
 
   return r;
 }
@@ -263,7 +263,7 @@ int __wasilibc_find_abspath(const char *path, const char **abs_prefix,
   // recently added preopens take precedence over less recently addded ones.
   size_t match_len = 0;
   int fd = -1;
-  STRONG_LOCK(lock);
+  LOCK(lock);
   for (size_t i = num_preopens; i > 0; --i) {
     const preopen *pre = &preopens[i - 1];
     const char *prefix = pre->prefix;
@@ -278,7 +278,7 @@ int __wasilibc_find_abspath(const char *path, const char **abs_prefix,
       *abs_prefix = prefix;
     }
   }
-  STRONG_UNLOCK(lock);
+  UNLOCK(lock);
 
   if (fd == -1) {
     errno = ENOENT;
@@ -306,11 +306,11 @@ void __wasilibc_populate_preopens(void) {
     return;
   }
 
-  STRONG_LOCK(lock);
+  LOCK(lock);
 
   // Check whether another thread initialized the preopens already.
   if (preopens_populated) {
-    STRONG_UNLOCK(lock);
+    UNLOCK(lock);
     return;
   }
 
@@ -381,7 +381,7 @@ void __wasilibc_populate_preopens(void) {
   // Preopens are now initialized.
   preopens_populated = true;
 
-  STRONG_UNLOCK(lock);
+  UNLOCK(lock);
 
   return;
 #ifdef __wasip1__
@@ -393,7 +393,7 @@ void __wasilibc_populate_preopens(void) {
 }
 
 void __wasilibc_reset_preopens(void) {
-  STRONG_LOCK(lock);
+  LOCK(lock);
 
   if (num_preopens) {
     for (int i = 0; i < num_preopens; ++i) {
@@ -410,5 +410,5 @@ void __wasilibc_reset_preopens(void) {
 
   assert_invariants();
 
-  STRONG_UNLOCK(lock);
+  UNLOCK(lock);
 }

From 94dd50313ab9efa464d10872122df78b1f528ed8 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 20:27:32 +0000
Subject: [PATCH 09/28] Change cwd locking

---
 libc-bottom-half/sources/getcwd.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/libc-bottom-half/sources/getcwd.c b/libc-bottom-half/sources/getcwd.c
index 576508620..1c7276645 100644
--- a/libc-bottom-half/sources/getcwd.c
+++ b/libc-bottom-half/sources/getcwd.c
@@ -8,27 +8,32 @@ char *__wasilibc_cwd = "/";
 
 #ifdef _REENTRANT
 static __lock_t lock[1];
+// Critical section contains no yield points, so we can use weak locks.
+void __wasilibc_cwd_lock(void) { WEAK_LOCK(lock); }
+void __wasilibc_cwd_unlock(void) { WEAK_UNLOCK(lock); }
+#else
+#define __wasilibc_cwd_lock() (void)0
+#define __wasilibc_cwd_unlock() (void)0
 #endif
 
 char *getcwd(char *buf, size_t size) {
-  // Critical section contains no yield points, so we can use weak locks.
-  WEAK_LOCK(lock);
+  __wasilibc_cwd_lock();
   if (!buf) {
     buf = strdup(__wasilibc_cwd);
     if (!buf) {
       errno = ENOMEM;
-      WEAK_UNLOCK(lock);
+      __wasilibc_cwd_unlock();
       return NULL;
     }
   } else {
     size_t len = strlen(__wasilibc_cwd);
     if (size < len + 1) {
       errno = ERANGE;
-      WEAK_UNLOCK(lock);
+      __wasilibc_cwd_unlock();
       return NULL;
     }
     strcpy(buf, __wasilibc_cwd);
   }
-  WEAK_UNLOCK(lock);
+  __wasilibc_cwd_unlock();
   return buf;
 }

From 5d6abcf22ac2166e893fd02a00dc45415db1f768 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 20:39:30 +0000
Subject: [PATCH 10/28] Build fixes

---
 libc-top-half/musl/src/stdio/__lockfile.c     |  1 +
 .../musl/src/thread/wasi-threads/__wait.c     | 25 +++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/libc-top-half/musl/src/stdio/__lockfile.c b/libc-top-half/musl/src/stdio/__lockfile.c
index 77878783a..a325ffe40 100644
--- a/libc-top-half/musl/src/stdio/__lockfile.c
+++ b/libc-top-half/musl/src/stdio/__lockfile.c
@@ -1,5 +1,6 @@
 #include "stdio_impl.h"
 #include "pthread_impl.h"
+#inculde <wasi/version.h>
 
 #ifdef __wasi_cooperative_threads__
 #include "lock.h"
diff --git a/libc-top-half/musl/src/thread/wasi-threads/__wait.c b/libc-top-half/musl/src/thread/wasi-threads/__wait.c
index 9484c0f3d..8248571f9 100644
--- a/libc-top-half/musl/src/thread/wasi-threads/__wait.c
+++ b/libc-top-half/musl/src/thread/wasi-threads/__wait.c
@@ -64,3 +64,28 @@ void __wait(volatile int *addr, volatile int *waiters, int val, int priv)
 	}
 	if (waiters) a_dec(waiters);
 }
+
+void __wake(volatile void *addr, int cnt, int priv)
+{
+	if (priv) priv = FUTEX_PRIVATE;
+	if (cnt<0) cnt = INT_MAX;
+#ifdef __wasilibc_unmodified_upstream
+	__syscall(SYS_futex, addr, FUTEX_WAKE|priv, cnt) != -ENOSYS ||
+	__syscall(SYS_futex, addr, FUTEX_WAKE, cnt);
+#else
+#ifdef _REENTRANT
+	__builtin_wasm_memory_atomic_notify((int*)addr, cnt);
+#endif
+#endif
+}
+
+void __futexwait(volatile void *addr, int val, int priv)
+{
+#ifdef __wasilibc_unmodified_upstream
+	if (priv) priv = FUTEX_PRIVATE;
+	__syscall(SYS_futex, addr, FUTEX_WAIT|priv, val, 0) != -ENOSYS ||
+	__syscall(SYS_futex, addr, FUTEX_WAIT, val, 0);
+#else
+	__wait(addr, NULL, val, priv);
+#endif
+}
\ No newline at end of file

From cf950b7901ab05c4485a70f9a514476b0240cd5e Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 20:42:22 +0000
Subject: [PATCH 11/28] Build fixes

---
 libc-top-half/musl/src/stdio/__lockfile.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libc-top-half/musl/src/stdio/__lockfile.c b/libc-top-half/musl/src/stdio/__lockfile.c
index a325ffe40..25b19e60c 100644
--- a/libc-top-half/musl/src/stdio/__lockfile.c
+++ b/libc-top-half/musl/src/stdio/__lockfile.c
@@ -1,6 +1,6 @@
 #include "stdio_impl.h"
 #include "pthread_impl.h"
-#inculde <wasi/version.h>
+#include <wasi/version.h>
 
 #ifdef __wasi_cooperative_threads__
 #include "lock.h"

From 4311c910ee9457f139198fa99c709d5f5de52fcf Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 20:48:24 +0000
Subject: [PATCH 12/28] Symbol fixes

---
 expected/wasm32-wasip1/defined-symbols.txt | 2 ++
 libc-top-half/musl/src/exit/atexit.c       | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/expected/wasm32-wasip1/defined-symbols.txt b/expected/wasm32-wasip1/defined-symbols.txt
index 562d70527..3dc1c6f78 100644
--- a/expected/wasm32-wasip1/defined-symbols.txt
+++ b/expected/wasm32-wasip1/defined-symbols.txt
@@ -75,6 +75,7 @@ __ftello
 __ftello_unlocked
 __funcs_on_exit
 __funcs_on_quick_exit
+__futexwait
 __futimesat
 __fwritable
 __fwritex
@@ -285,6 +286,7 @@ __uflow
 __unlist_locked_file
 __uselocale
 __utc
+__wait
 __wasi_args_get
 __wasi_args_sizes_get
 __wasi_clock_res_get
diff --git a/libc-top-half/musl/src/exit/atexit.c b/libc-top-half/musl/src/exit/atexit.c
index d52ae8267..f13d540a0 100644
--- a/libc-top-half/musl/src/exit/atexit.c
+++ b/libc-top-half/musl/src/exit/atexit.c
@@ -26,7 +26,7 @@ static int slot;
 
 // All locks here can be weak, because the locking is only needed to protect against
 // concurrent manipulation of the handler table, which hits no context switch points.
-__lock_t lock[1];
+static __lock_t lock[1];
 __lock_t *const __atexit_lockptr = lock;
 #endif
 

From f68bf5a76d9b5c36276dd4ccc0717759cc44653e Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 20:52:24 +0000
Subject: [PATCH 13/28] Symbol fixes

---
 expected/wasm32-wasip1-threads/defined-symbols.txt | 1 +
 expected/wasm32-wasip1/defined-symbols.txt         | 2 --
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/expected/wasm32-wasip1-threads/defined-symbols.txt b/expected/wasm32-wasip1-threads/defined-symbols.txt
index 4fb5d53fc..332ae8e39 100644
--- a/expected/wasm32-wasip1-threads/defined-symbols.txt
+++ b/expected/wasm32-wasip1-threads/defined-symbols.txt
@@ -81,6 +81,7 @@ __ftello
 __ftello_unlocked
 __funcs_on_exit
 __funcs_on_quick_exit
+__futexwait
 __futimesat
 __fwritable
 __fwritex
diff --git a/expected/wasm32-wasip1/defined-symbols.txt b/expected/wasm32-wasip1/defined-symbols.txt
index 3dc1c6f78..562d70527 100644
--- a/expected/wasm32-wasip1/defined-symbols.txt
+++ b/expected/wasm32-wasip1/defined-symbols.txt
@@ -75,7 +75,6 @@ __ftello
 __ftello_unlocked
 __funcs_on_exit
 __funcs_on_quick_exit
-__futexwait
 __futimesat
 __fwritable
 __fwritex
@@ -286,7 +285,6 @@ __uflow
 __unlist_locked_file
 __uselocale
 __utc
-__wait
 __wasi_args_get
 __wasi_args_sizes_get
 __wasi_clock_res_get

From 73081cf5298f3636f74701cdbd9d0ffb731057dd Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 20:59:09 +0000
Subject: [PATCH 14/28] Symbol fixes

---
 expected/wasm32-wasip1-threads/defined-symbols.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/expected/wasm32-wasip1-threads/defined-symbols.txt b/expected/wasm32-wasip1-threads/defined-symbols.txt
index 332ae8e39..1d2f3c63c 100644
--- a/expected/wasm32-wasip1-threads/defined-symbols.txt
+++ b/expected/wasm32-wasip1-threads/defined-symbols.txt
@@ -309,6 +309,7 @@ __unlockfile
 __uselocale
 __utc
 __wait
+__wake
 __wasi_args_get
 __wasi_args_sizes_get
 __wasi_clock_res_get

From 47e08ba05d8e43f344d550a50590c04d5f6d20a7 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 21:01:31 +0000
Subject: [PATCH 15/28] Disable shared builds

---
 CMakeLists.txt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5e261d183..63f20aa17 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,7 +68,8 @@ elseif(TARGET_TRIPLE MATCHES "-wasip2$")
   set(SHARED ON)
 elseif(TARGET_TRIPLE MATCHES "-wasip3$")
   set(WASI p3)
-  set(SHARED ON)
+  # TODO: There are currently issues with shared libraries on wasip3, so disable for now.
+  set(SHARED OFF)
 else()
   message(FATAL_ERROR "Unknown WASI target triple: ${TARGET_TRIPLE}")
 endif()

From 1210dca331a86c87c809548125dfcc524c097ca3 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 21:32:10 +0000
Subject: [PATCH 16/28] Update symbols for WASIP3

---
 expected/wasm32-wasip3/defined-symbols.txt   | 32 ++++++++++++++++++++
 expected/wasm32-wasip3/predefined-macros.txt |  4 +++
 expected/wasm32-wasip3/undefined-symbols.txt | 20 ++++++++++++
 3 files changed, 56 insertions(+)

diff --git a/expected/wasm32-wasip3/defined-symbols.txt b/expected/wasm32-wasip3/defined-symbols.txt
index 61ac1ad71..ff13a6498 100644
--- a/expected/wasm32-wasip3/defined-symbols.txt
+++ b/expected/wasm32-wasip3/defined-symbols.txt
@@ -12,8 +12,11 @@ __ENOMEM
 __SIG_ERR
 __SIG_IGN
 __acquire_ptc
+__aio_close
 __asctime_r
 __assert_fail
+__at_quick_exit_lockptr
+__atexit_lockptr
 __c_dot_utf8
 __c_dot_utf8_locale
 __c_locale
@@ -22,6 +25,7 @@ __clock_gettime
 __clock_nanosleep
 __component_type_object_force_link_wasip3
 __component_type_object_force_link_wasip3_public_use_in_this_compilation_unit
+__copy_tls
 __cos
 __cosdf
 __cosl
@@ -143,7 +147,11 @@ __libc_calloc
 __libc_free
 __libc_malloc
 __loc_is_allocated
+__locale_lock
+__locale_lockptr
 __localtime_r
+__lock
+__lockfile
 __log2_data
 __log2f_data
 __log_data
@@ -208,6 +216,7 @@ __pthread_tsd_size
 __putenv
 __qsort_r
 __rand48_step
+__random_lockptr
 __reallocarray
 __release_ptc
 __rem_pio2
@@ -235,6 +244,7 @@ __stdin_used
 __stdio_close
 __stdio_exit
 __stdio_exit_needed
+__stdio_ofl_lockptr
 __stdio_read
 __stdio_seek
 __stdio_write
@@ -266,6 +276,7 @@ __tan
 __tandf
 __tanl
 __testcancel
+__thread_list_lock
 __tl_lock
 __tl_unlock
 __tm_to_secs
@@ -285,8 +296,13 @@ __tre_mem_new_impl
 __tsearch_balance
 __uflow
 __unlist_locked_file
+__unlock
+__unlockfile
 __uselocale
 __utc
+__waitlist_wait_on
+__waitlist_wake_all
+__waitlist_wake_one
 __wasi_init_tp
 __wasi_sockets_services_db
 __wasi_sockets_utils__any_addr
@@ -303,6 +319,8 @@ __wasilibc_add_file
 __wasilibc_add_tcp_socket
 __wasilibc_add_udp_socket
 __wasilibc_cwd
+__wasilibc_cwd_lock
+__wasilibc_cwd_unlock
 __wasilibc_deinitialize_environ
 __wasilibc_dttoif
 __wasilibc_ensure_environ
@@ -1466,7 +1484,9 @@ vwscanf
 wasip3_backpressure_dec
 wasip3_backpressure_inc
 wasip3_context_get_0
+wasip3_context_get_1
 wasip3_context_set_0
+wasip3_context_set_1
 wasip3_list_string_free
 wasip3_list_tuple2_string_string_free
 wasip3_list_u8_free
@@ -1479,7 +1499,19 @@ wasip3_subtask_block_on
 wasip3_subtask_cancel
 wasip3_subtask_drop
 wasip3_task_cancel
+wasip3_thread_index
+wasip3_thread_new_indirect
+wasip3_thread_suspend
+wasip3_thread_suspend_cancellable
+wasip3_thread_suspend_to
+wasip3_thread_suspend_to_cancellable
+wasip3_thread_suspend_to_suspended
+wasip3_thread_suspend_to_suspended_cancellable
+wasip3_thread_unsuspend
 wasip3_thread_yield
+wasip3_thread_yield_cancellable
+wasip3_thread_yield_to_suspended
+wasip3_thread_yield_to_suspended_cancellable
 wasip3_tuple2_string_string_free
 wasip3_waitable_block_on
 wasip3_waitable_join
diff --git a/expected/wasm32-wasip3/predefined-macros.txt b/expected/wasm32-wasip3/predefined-macros.txt
index 8e2f62089..ac77e6d35 100644
--- a/expected/wasm32-wasip3/predefined-macros.txt
+++ b/expected/wasm32-wasip3/predefined-macros.txt
@@ -1734,6 +1734,8 @@
 #define SEEK_SET 0
 #define SEGSIZE 512
 #define SEM_FAILED ((sem_t *)0)
+#define SEM_NSEMS_MAX 256
+#define SEM_VALUE_MAX 0x7fffffff
 #define SERVFAIL ns_r_servfail
 #define SHORTBITS (sizeof(short) * 8)
 #define SHRT_MAX 0x7fff
@@ -2429,6 +2431,7 @@
 #define _POSIX_VERSION 200809L
 #define _PTHREAD_H 
 #define _PTRDIFF_T 
+#define _REENTRANT 1
 #define _REGEX_H 
 #define _SCHED_H 
 #define _SC_2_CHAR_TERM 95
@@ -3133,6 +3136,7 @@
 #define __va_copy(d,s) __builtin_va_copy(d, s)
 #define __wasi__ 1
 #define __wasi_api_h 
+#define __wasi_cooperative_threads__ 
 #define __wasi_libc_busywait_h 
 #define __wasi_libc_environ_h 
 #define __wasi_libc_find_relpath_h 
diff --git a/expected/wasm32-wasip3/undefined-symbols.txt b/expected/wasm32-wasip3/undefined-symbols.txt
index a9d8a373b..d7b9b134e 100644
--- a/expected/wasm32-wasip3/undefined-symbols.txt
+++ b/expected/wasm32-wasip3/undefined-symbols.txt
@@ -2,7 +2,9 @@ __addtf3
 __backpressure_dec
 __backpressure_inc
 __context_get_0
+__context_get_1
 __context_set_0
+__context_set_1
 __data_end
 __divtf3
 __eqtf2
@@ -26,7 +28,20 @@ __subtask_cancel
 __subtask_drop
 __subtf3
 __task_cancel
+__thread_index
+__thread_new_indirect
+__thread_suspend
+__thread_suspend_cancellable
+__thread_suspend_to
+__thread_suspend_to_cancellable
+__thread_suspend_to_suspended
+__thread_suspend_to_suspended_cancellable
+__thread_unsuspend
 __thread_yield
+__thread_yield_cancellable
+__thread_yield_to_suspended
+__thread_yield_to_suspended_cancellable
+__tls_align
 __trunctfdf2
 __trunctfsf2
 __unordtf2
@@ -36,6 +51,10 @@ __waitable_set_new
 __waitable_set_poll
 __waitable_set_wait
 __wasm_call_ctors
+__wasm_component_model_builtin_context_get_0
+__wasm_component_model_builtin_context_get_1
+__wasm_component_model_builtin_context_set_0
+__wasm_first_page_end
 __wasm_import_environment_get_arguments
 __wasm_import_environment_get_environment
 __wasm_import_environment_get_initial_cwd
@@ -129,6 +148,7 @@ __wasm_import_terminal_output_terminal_output_drop
 __wasm_import_terminal_stderr_get_terminal_stderr
 __wasm_import_terminal_stdin_get_terminal_stdin
 __wasm_import_terminal_stdout_get_terminal_stdout
+__wasm_init_tls
 filesystem_future_result_void_error_code__cancel_read
 filesystem_future_result_void_error_code__cancel_write
 filesystem_future_result_void_error_code__drop_readable

From e7407c7b45deb5f5ea68153df51600c1bf6f9c4d Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 21:41:14 +0000
Subject: [PATCH 17/28] Bump wasm-component-ld

---
 cmake/wasm-component-ld.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/wasm-component-ld.cmake b/cmake/wasm-component-ld.cmake
index 2e7976602..0314df308 100644
--- a/cmake/wasm-component-ld.cmake
+++ b/cmake/wasm-component-ld.cmake
@@ -10,7 +10,7 @@ if (NOT WASM_COMPONENT_LD_EXECUTABLE)
   ba_download(
     wasm-component-ld
     "https://github.com/bytecodealliance/wasm-component-ld"
-    "v0.5.19"
+    "v0.5.20"
   )
   ExternalProject_Get_Property(wasm-component-ld SOURCE_DIR)
   set(WASM_COMPONENT_LD_EXECUTABLE "${SOURCE_DIR}/wasm-component-ld")

From 29fb9846bc63ed6217f9ec3f9834eb5775471898 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 21:42:51 +0000
Subject: [PATCH 18/28] Undefined signal fix

---
 expected/wasm32-wasip3/undefined-symbols.txt | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/expected/wasm32-wasip3/undefined-symbols.txt b/expected/wasm32-wasip3/undefined-symbols.txt
index 6f3689463..d7b9b134e 100644
--- a/expected/wasm32-wasip3/undefined-symbols.txt
+++ b/expected/wasm32-wasip3/undefined-symbols.txt
@@ -41,10 +41,7 @@ __thread_yield
 __thread_yield_cancellable
 __thread_yield_to_suspended
 __thread_yield_to_suspended_cancellable
-<<<<<<< sy/wasip3-locks
 __tls_align
-=======
->>>>>>> main
 __trunctfdf2
 __trunctfsf2
 __unordtf2

From 28d741f30215a7d0da4e4a2812c3c5bb774e30b5 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 22:41:52 +0000
Subject: [PATCH 19/28] Bump wasm-component-ld

---
 cmake/wasm-component-ld.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/wasm-component-ld.cmake b/cmake/wasm-component-ld.cmake
index 0314df308..d0b8b417e 100644
--- a/cmake/wasm-component-ld.cmake
+++ b/cmake/wasm-component-ld.cmake
@@ -10,7 +10,7 @@ if (NOT WASM_COMPONENT_LD_EXECUTABLE)
   ba_download(
     wasm-component-ld
     "https://github.com/bytecodealliance/wasm-component-ld"
-    "v0.5.20"
+    "v0.5.21"
   )
   ExternalProject_Get_Property(wasm-component-ld SOURCE_DIR)
   set(WASM_COMPONENT_LD_EXECUTABLE "${SOURCE_DIR}/wasm-component-ld")

From 93ab9e4b31d2721a880d0f8efb53e48f690c544f Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 22:46:49 +0000
Subject: [PATCH 20/28] Symbol fixes

---
 expected/wasm32-wasip3/predefined-macros.txt | 1 +
 expected/wasm32-wasip3/undefined-symbols.txt | 5 -----
 2 files changed, 1 insertion(+), 5 deletions(-)

diff --git a/expected/wasm32-wasip3/predefined-macros.txt b/expected/wasm32-wasip3/predefined-macros.txt
index ac77e6d35..f4176082a 100644
--- a/expected/wasm32-wasip3/predefined-macros.txt
+++ b/expected/wasm32-wasip3/predefined-macros.txt
@@ -3210,6 +3210,7 @@
 #define __wasm32 1
 #define __wasm32__ 1
 #define __wasm__ 1
+#define __wasm_atomics__ 1
 #define _tolower(a) ((a)|0x20)
 #define _toupper(a) ((a)&0x5f)
 #define acos(x) __tg_real_complex(acos, (x))
diff --git a/expected/wasm32-wasip3/undefined-symbols.txt b/expected/wasm32-wasip3/undefined-symbols.txt
index d7b9b134e..bba58ed57 100644
--- a/expected/wasm32-wasip3/undefined-symbols.txt
+++ b/expected/wasm32-wasip3/undefined-symbols.txt
@@ -50,11 +50,6 @@ __waitable_set_drop
 __waitable_set_new
 __waitable_set_poll
 __waitable_set_wait
-__wasm_call_ctors
-__wasm_component_model_builtin_context_get_0
-__wasm_component_model_builtin_context_get_1
-__wasm_component_model_builtin_context_set_0
-__wasm_first_page_end
 __wasm_import_environment_get_arguments
 __wasm_import_environment_get_environment
 __wasm_import_environment_get_initial_cwd

From bf037e98c6ff73638a95fe9a197c52d0a7dd444a Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 22:50:59 +0000
Subject: [PATCH 21/28] Add __wasm_call_ctors to undefined

---
 expected/wasm32-wasip3/undefined-symbols.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/expected/wasm32-wasip3/undefined-symbols.txt b/expected/wasm32-wasip3/undefined-symbols.txt
index bba58ed57..2d644ca97 100644
--- a/expected/wasm32-wasip3/undefined-symbols.txt
+++ b/expected/wasm32-wasip3/undefined-symbols.txt
@@ -50,6 +50,7 @@ __waitable_set_drop
 __waitable_set_new
 __waitable_set_poll
 __waitable_set_wait
+__wasm_call_ctors
 __wasm_import_environment_get_arguments
 __wasm_import_environment_get_environment
 __wasm_import_environment_get_initial_cwd

From 4bd86350649de127e3e175b87c6229b710e513e1 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Fri, 20 Feb 2026 22:55:14 +0000
Subject: [PATCH 22/28] Add component-model-threading feature

---
 test/CMakeLists.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index bb51b2c05..d24aeec96 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -126,6 +126,7 @@ function(register_test test_name executable_name)
   endif()
   if (WASI STREQUAL "p3")
     list(APPEND wasmtime_args --wasm component-model-async)
+    list(APPEND wasmtime_args --wasm component-model-threading)
     list(APPEND wasmtime_args --wasi p3)
   endif()
 

From a19d2cf45d7cc216530daf348395f5d20deb9a13 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Sat, 21 Feb 2026 10:25:11 +0000
Subject: [PATCH 23/28] Fix locks

---
 libc-top-half/musl/src/stdio/vsnprintf.c | 2 +-
 libc-top-half/musl/src/stdio/vswprintf.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libc-top-half/musl/src/stdio/vsnprintf.c b/libc-top-half/musl/src/stdio/vsnprintf.c
index 48c3aef7e..4d8366baf 100644
--- a/libc-top-half/musl/src/stdio/vsnprintf.c
+++ b/libc-top-half/musl/src/stdio/vsnprintf.c
@@ -41,7 +41,7 @@ int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list ap)
 		.lbf = EOF,
 		.write = sn_write,
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-		.lock = -1,
+		.lock = __STDIO_LOCK_INIT,
 #endif
 		.buf = buf,
 		.cookie = &c,
diff --git a/libc-top-half/musl/src/stdio/vswprintf.c b/libc-top-half/musl/src/stdio/vswprintf.c
index cab94cba7..d17da02ba 100644
--- a/libc-top-half/musl/src/stdio/vswprintf.c
+++ b/libc-top-half/musl/src/stdio/vswprintf.c
@@ -44,7 +44,7 @@ int vswprintf(wchar_t *restrict s, size_t n, const wchar_t *restrict fmt, va_lis
 		.lbf = EOF,
 		.write = sw_write,
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-		.lock = -1,
+		.lock = __STDIO_LOCK_INIT,
 #endif
 		.buf = buf,
 		.buf_size = sizeof buf,

From 207dc0d8b54561b864aaf09c08ce92c20a6a200d Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Sat, 21 Feb 2026 10:30:58 +0000
Subject: [PATCH 24/28] Fix shared linking

---
 CMakeLists.txt                               | 3 +--
 libc-top-half/musl/src/internal/stdio_impl.h | 5 +++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 63f20aa17..5e261d183 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,8 +68,7 @@ elseif(TARGET_TRIPLE MATCHES "-wasip2$")
   set(SHARED ON)
 elseif(TARGET_TRIPLE MATCHES "-wasip3$")
   set(WASI p3)
-  # TODO: There are currently issues with shared libraries on wasip3, so disable for now.
-  set(SHARED OFF)
+  set(SHARED ON)
 else()
   message(FATAL_ERROR "Unknown WASI target triple: ${TARGET_TRIPLE}")
 endif()
diff --git a/libc-top-half/musl/src/internal/stdio_impl.h b/libc-top-half/musl/src/internal/stdio_impl.h
index 7ea811393..cfd476715 100644
--- a/libc-top-half/musl/src/internal/stdio_impl.h
+++ b/libc-top-half/musl/src/internal/stdio_impl.h
@@ -84,8 +84,9 @@ extern hidden FILE *volatile __stdout_used;
 extern hidden FILE *volatile __stderr_used;
 
 #if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
-hidden int __lockfile(FILE *);
-hidden void __unlockfile(FILE *);
+// Needs to be unhidden because they're used by the emulated signal implementation
+int __lockfile(FILE *);
+void __unlockfile(FILE *);
 #endif
 
 hidden size_t __stdio_read(FILE *, unsigned char *, size_t);

From a6ffb7e329d6ef69cfed8a095c4bc7f07723050c Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Sat, 21 Feb 2026 10:39:45 +0000
Subject: [PATCH 25/28] Retrigger CI


From 518371afb4c896ea4d1df740d700dd4ed2523ece Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Sat, 21 Feb 2026 10:53:41 +0000
Subject: [PATCH 26/28] Change init lock

---
 libc-top-half/musl/src/thread/wasi-threads/pthread_create.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libc-top-half/musl/src/thread/wasi-threads/pthread_create.c b/libc-top-half/musl/src/thread/wasi-threads/pthread_create.c
index 879b48c1f..4d1c02f16 100644
--- a/libc-top-half/musl/src/thread/wasi-threads/pthread_create.c
+++ b/libc-top-half/musl/src/thread/wasi-threads/pthread_create.c
@@ -349,7 +349,9 @@ weak_alias(dummy_file, __stderr_used);
 
 static void init_file_lock(FILE *f)
 {
+#ifndef __wasi_cooperative_threads__
 	if (f && f->lock<0) f->lock = 0;
+#endif
 }
 
 int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp, void *(*entry)(void *), void *restrict arg)

From 4fb6925213248759a81db7ed38572f03d26b013c Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Sat, 21 Feb 2026 11:00:09 +0000
Subject: [PATCH 27/28] Disable dynamic linking

---
 CMakeLists.txt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5e261d183..b3bb3c019 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,7 +68,8 @@ elseif(TARGET_TRIPLE MATCHES "-wasip2$")
   set(SHARED ON)
 elseif(TARGET_TRIPLE MATCHES "-wasip3$")
   set(WASI p3)
-  set(SHARED ON)
+  # There seems to be some dynamic linking issues, especially with errno, for waspi3
+  set(SHARED OFF)
 else()
   message(FATAL_ERROR "Unknown WASI target triple: ${TARGET_TRIPLE}")
 endif()

From 29f8f5135c2b8bfe1a3b18978378f72431f92c14 Mon Sep 17 00:00:00 2001
From: Sy Brand <sy.brand@fastly.com>
Date: Sat, 21 Feb 2026 11:04:20 +0000
Subject: [PATCH 28/28] Reenable shared lib

---
 CMakeLists.txt | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b3bb3c019..5e261d183 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,8 +68,7 @@ elseif(TARGET_TRIPLE MATCHES "-wasip2$")
   set(SHARED ON)
 elseif(TARGET_TRIPLE MATCHES "-wasip3$")
   set(WASI p3)
-  # There seems to be some dynamic linking issues, especially with errno, for waspi3
-  set(SHARED OFF)
+  set(SHARED ON)
 else()
   message(FATAL_ERROR "Unknown WASI target triple: ${TARGET_TRIPLE}")
 endif()