[pthreads] Initialize TLS on workers in MINIMAL_RUNTIME mode. (#24646)

TLS was not initialized on workers causing the tls_base address to be 0
and write to the wrong memory location.

Fixes #21528 and is also needed for PR #24565

Author: brendandahl

src/postamble_minimal.js

@@ -51,7 +51,8 @@ function initRuntime(wasmExports) {
 #endif
 
 #if PTHREADS
-  if (ENVIRONMENT_IS_PTHREAD) return
+  PThread.tlsInitFunctions.push(wasmExports['_emscripten_tls_init']);
+  if (ENVIRONMENT_IS_PTHREAD) return;
 #endif
 
 #if WASM_WORKERS
@@ -66,10 +67,6 @@ function initRuntime(wasmExports) {
   writeStackCookie();
 #endif
 
-#if PTHREADS
-  PThread.tlsInitFunctions.push(wasmExports['_emscripten_tls_init']);
-#endif
-
   <<< ATINITS >>>
 
 #if hasExportedSymbol('__wasm_call_ctors')

test/pthread/test_pthread_c_thread_local.c

@@ -0,0 +1,35 @@
+// Copyright 2025 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <pthread.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <stdio.h>
+
+static _Thread_local int thread_local = 0;
+
+void *thread_start(void *arg) {
+  thread_local = 1;
+  assert(thread_local == 1);
+  printf("thread_local=%d\n", thread_local);
+  return NULL;
+}
+
+int main() {
+  thread_local = 2;
+  pthread_t thread;
+  int rc;
+
+  rc = pthread_create(&thread, NULL, thread_start, NULL);
+  assert(rc == 0);
+
+  rc = pthread_join(thread, NULL);
+  assert(rc == 0);
+
+  printf("thread_local=%d\n", thread_local);
+  assert(thread_local == 2);
+  printf("done\n");
+  return 0;
+}

test/pthread/test_pthread_c_thread_local.out

@@ -0,0 +1,3 @@
+thread_local=1
+thread_local=2
+done

test/test_core.py

@@ -2636,6 +2636,13 @@ def test_pthread_thread_local_storage(self):
       self.set_setting('INITIAL_MEMORY', '300mb')
     self.do_run_in_out_file_test('pthread/test_pthread_thread_local_storage.cpp')
 
+  @node_pthreads
+  @also_with_minimal_runtime
+  def test_pthread_c_thread_local(self):
+    if self.get_setting('MINIMAL_RUNTIME') and is_sanitizing(self.cflags):
+      self.skipTest('MINIMAL_RUNTIME + threads + asan does not work')
+    self.do_run_in_out_file_test('pthread/test_pthread_c_thread_local.c')
+
   @node_pthreads
   def test_pthread_cleanup(self):
     self.set_setting('PTHREAD_POOL_SIZE', 4)