Make longjmp/exceptions helpers thread-safe (#12056)

This adds the thread-local annotation to those globals. Previously they were in
JS, which is effectively thread-local, but then we moved them to C which meant
they were stored in the same shared memory for all threads. A race could
happen if threads (or longjmp) operations happened at just the right time, one
writing to those globals and another reading.

Also make compiler-rt now build with a multithreaded variation, as the implementation
of those globals is in that library.

Also add a testcase that runs exceptions on multiple threads. It's not a guaranteed
way to notice a race, but it may help, and this is an area we didn't have coverage
of.

Fixes #12035

This has been a possible race condition for a very long time. I think it went
unnoticed because exceptions and longjmp tend to be used for exceptional
things, and not constantly being executed. And also until we get wasm
exceptions support they are also slow, so people have been trying to avoid
them as much as possible anyhow.

Author: kripken

system/lib/compiler-rt/extras.c renamed to system/lib/compiler-rt/emscripten_exception_builtins.c

@@ -5,14 +5,14 @@
  * found in the LICENSE file.
  *
  * Support functions for emscripten setjmp/longjmp and exception handling
- * support.
+ * support. References to the things below are generated in the LLVM backend.
  * See: https://llvm.org/doxygen/WebAssemblyLowerEmscriptenEHSjLj_8cpp.html
  */
 
-/* References to these globals are generated in the llvm backend so they
- * cannot be static */
-int __THREW__ = 0;
-int __threwValue = 0;
+#include <threads.h>
+
+thread_local int __THREW__ = 0;
+thread_local int __threwValue = 0;
 
 void setThrew(int threw, int value) {
   if (__THREW__ == 0) {

system/lib/libc/extras.c

@@ -30,4 +30,3 @@ long* _get_timezone() {
 
 void __lock(void* ptr) {}
 void __unlock(void* ptr) {}
-

tests/core/pthread/exceptions.cpp

@@ -0,0 +1,73 @@
+// Copyright 2019 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 <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <assert.h>
+#include <emscripten.h>
+
+#include <atomic>
+
+#define NUM_THREADS 2
+#define TOTAL 1000
+#define THREAD_ADDS 750
+#define MAIN_ADDS 5
+
+static std::atomic<int> sum;
+static std::atomic<int> total;
+
+void *ThreadMain(void *arg) {
+  for (int i = 0; i < TOTAL; i++) {
+    try {
+      // Throw two different types, to make sure we check throwing and landing
+      // pad behavior.
+      if (i & 3) {
+        throw 3.14159f;
+      }
+      throw i;
+    } catch (int x) {
+      total += x;
+    } catch (float f) {
+      sum++;
+      // wait for a change, so we see interleaved processing.
+      int last = sum.load();
+      while (sum.load() == last) {}
+    }
+  }
+  pthread_exit((void*)TOTAL);
+}
+
+pthread_t thread[NUM_THREADS];
+
+void CreateThread(int i)
+{
+  int rc = pthread_create(&thread[i], nullptr, ThreadMain, (void*)i);
+  assert(rc == 0);
+}
+
+void loop() {
+  static int main_adds = 0;
+  int worker_adds = sum.load() - main_adds;
+  sum++;
+  main_adds++;
+  printf("main iter %d : %d\n", main_adds, worker_adds);
+  if (worker_adds == NUM_THREADS * THREAD_ADDS &&
+      main_adds >= MAIN_ADDS) {
+    printf("done: %d.\n", total.load());
+    emscripten_cancel_main_loop();
+    exit(0);
+  }
+}
+
+int main() {
+  // Create initial threads.
+  for(int i = 0; i < NUM_THREADS; ++i) {
+    printf("maek\n");
+    CreateThread(i);
+  }
+
+  emscripten_set_main_loop(loop, 0, 0);
+}

tests/core/pthread/exceptions.out

@@ -0,0 +1 @@
+done: 249000.

tests/test_core.py

@@ -7750,7 +7750,6 @@ def test_stack_overflow_check(self):
     self.emcc_args += ['-DONE_BIG_STRING']
     self.do_runf(path_from_root('tests', 'stack_overflow.cpp'), 'stack overflow', assert_returncode=NON_ZERO)
 
-  @unittest.skip('let llvm roll in')
   @node_pthreads
   def test_binaryen_2170_emscripten_atomic_cas_u8(self):
     self.emcc_args += ['-s', 'USE_PTHREADS=1']
@@ -8163,7 +8162,6 @@ def test_fpic_static(self):
     self.emcc_args.append('-fPIC')
     self.do_run_in_out_file_test('tests', 'core', 'test_hello_world.c')
 
-  @unittest.skip('let llvm roll in')
   @node_pthreads
   def test_pthread_create(self):
     self.set_setting('-lbrowser.js')
@@ -8178,18 +8176,21 @@ def test():
     self.emcc_args += ['-DPOOL']
     test()
 
-  @unittest.skip('let llvm roll in')
+  @node_pthreads
+  def test_pthread_exceptions(self):
+    self.set_setting('PTHREAD_POOL_SIZE', '2')
+    self.emcc_args += ['-fexceptions']
+    self.do_run_in_out_file_test('tests', 'core', 'pthread', 'exceptions.cpp')
+
   def test_emscripten_atomics_stub(self):
     self.do_run_in_out_file_test('tests', 'core', 'pthread', 'emscripten_atomics.c')
 
-  @unittest.skip('let llvm roll in')
   @no_asan('incompatibility with atomics')
   @node_pthreads
   def test_emscripten_atomics(self):
     self.set_setting('USE_PTHREADS', '1')
     self.do_run_in_out_file_test('tests', 'core', 'pthread', 'emscripten_atomics.c')
 
-  @unittest.skip('let llvm roll in')
   @no_asan('incompatibility with atomics')
   @node_pthreads
   def test_emscripten_futexes(self):

tests/test_other.py

@@ -2563,7 +2563,6 @@ def test_fs_stream_proto(self):
       out = self.run_js('a.out.js', engine=engine)
       self.assertContained('File size: 724', out)
 
-  @unittest.skip('let llvm roll in')
   def test_node_emscripten_num_logical_cores(self):
     # Test with node.js that the emscripten_num_logical_cores method is working
     create_test_file('src.cpp', r'''
@@ -7890,7 +7889,6 @@ def test_node_js_run_from_different_directory(self):
     self.assertContained('hello, world!', ret)
 
   # Tests that a pthreads + modularize build can be run in node js
-  @unittest.skip('let llvm roll in')
   def test_node_js_pthread_module(self):
     # create module loader script
     moduleLoader = 'moduleLoader.js'
@@ -8816,7 +8814,6 @@ def test_asan_no_stack_trace(self):
   def test_asan_pthread_stubs(self):
     self.do_smart_test(path_from_root('tests', 'other', 'test_asan_pthread_stubs.c'), emcc_args=['-fsanitize=address', '-s', 'ALLOW_MEMORY_GROWTH=1'])
 
-  @unittest.skip('let llvm roll in')
   def test_proxy_to_pthread_stack(self):
     with js_engines_modify([NODE_JS + ['--experimental-wasm-threads', '--experimental-wasm-bulk-memory']]):
       self.do_smart_test(path_from_root('tests', 'other', 'test_proxy_to_pthread_stack.c'),
@@ -9212,7 +9209,6 @@ def test_backwards_deps_in_archive(self):
     self.run_process([EMCC, 'empty.c', '-la', '-L.'])
     self.assertContained('success', self.run_js('a.out.js'))
 
-  @unittest.skip('let llvm roll in')
   def test_warning_flags(self):
     self.run_process([EMCC, '-c', '-o', 'hello.o', path_from_root('tests', 'hello_world.c')])
     cmd = [EMCC, 'hello.o', '-o', 'a.js', '-g', '--closure', '1']

tools/system_libs.py

@@ -635,7 +635,7 @@ def get_default_variation(cls, **kwargs):
     return super(AsanInstrumentedLibrary, cls).get_default_variation(is_asan=shared.Settings.USE_ASAN, **kwargs)
 
 
-class libcompiler_rt(Library):
+class libcompiler_rt(MTLibrary):
   name = 'libcompiler_rt'
   # compiler_rt files can't currently be part of LTO although we are hoping to remove this
   # restriction soon: https://reviews.llvm.org/D71738
@@ -644,9 +644,9 @@ class libcompiler_rt(Library):
   cflags = ['-O2', '-fno-builtin']
   src_dir = ['system', 'lib', 'compiler-rt', 'lib', 'builtins']
   src_files = glob_in_path(src_dir, '*.c')
-  src_files.append(shared.path_from_root('system', 'lib', 'compiler-rt', 'extras.c'))
   src_files.append(shared.path_from_root('system', 'lib', 'compiler-rt', 'stack_ops.s'))
   src_files.append(shared.path_from_root('system', 'lib', 'compiler-rt', 'emscripten_setjmp.c'))
+  src_files.append(shared.path_from_root('system', 'lib', 'compiler-rt', 'emscripten_exception_builtins.c'))
 
 
 class libc(AsanInstrumentedLibrary, MuslInternalLibrary, MTLibrary):