Add support for C++ thread safe statics

libc/runtime/cxaguard.c

@@ -0,0 +1,114 @@
+/*
+ * Copyright (C) 2006 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "libc/atomic.h"
+#include "libc/intrin/atomic.h"
+#include "libc/limits.h"
+#include "third_party/nsync/futex.internal.h"
+
+// This file contains C++ ABI support functions for one time
+// constructors as defined in the "Run-time ABI for the ARM Architecture"
+// section 4.4.2
+//
+// ARM C++ ABI and Itanium/x86 C++ ABI has different definition for
+// one time construction:
+//
+//    ARM C++ ABI defines the LSB of guard variable should be tested
+//    by compiler-generated code before calling __cxa_guard_acquire et al.
+//
+//    The Itanium/x86 C++ ABI defines the low-order _byte_ should be
+//    tested instead.
+//
+//    Meanwhile, guard variable are 32bit aligned for ARM, and 64bit
+//    aligned for x86.
+//
+// Reference documentation:
+//
+//    section 3.2.3 of ARM IHI 0041C (for ARM)
+//    section 3.3.2 of the Itanium C++ ABI specification v1.83 (for x86).
+//
+// There is no C++ ABI available for other ARCH. But the gcc source
+// shows all other ARCH follow the definition of Itanium/x86 C++ ABI.
+
+// The Itanium/x86 C++ ABI (used by all architectures that aren't ARM32)
+// mandates guard variables are 64-bit aligned, 64-bit values. The least
+// significant byte is tested by the compiler-generated code before it's
+// calling __cxa_guard_acquire.
+union CxaGuardValue {
+  atomic_int state;
+  int64_t aligner;
+};
+
+// Set construction state values according to reference documentation. 0
+// is the initialization value. Arm requires ((*gv & 1) == 1) after
+// __cxa_guard_release, ((*gv & 3) == 0) after __cxa_guard_abort. X86
+// requires first byte not modified by __cxa_guard_acquire, first byte
+// is non-zero after __cxa_guard_release.
+#define CONSTRUCTION_NOT_YET_STARTED         0
+#define CONSTRUCTION_COMPLETE                1
+#define CONSTRUCTION_UNDERWAY_WITHOUT_WAITER 0x100
+#define CONSTRUCTION_UNDERWAY_WITH_WAITER    0x200
+
+int __cxa_guard_acquire(union CxaGuardValue *gv) {
+  int old_value = atomic_load_explicit(&gv->state, memory_order_relaxed);
+  while (true) {
+    if (old_value == CONSTRUCTION_COMPLETE) {
+      // A load_acquire operation is needed before exiting with COMPLETE
+      // state, as we must ensure that all the stores performed by the
+      // construction function are observable on this CPU after we exit.
+      atomic_thread_fence(memory_order_acquire);
+      return 0;
+    } else if (old_value == CONSTRUCTION_NOT_YET_STARTED) {
+      if (!atomic_compare_exchange_weak_explicit(
+              &gv->state, &old_value, CONSTRUCTION_UNDERWAY_WITHOUT_WAITER,
+              memory_order_relaxed, memory_order_relaxed)) {
+        continue;
+      }
+      // The acquire fence may not be needed. But as described in section 3.3.2
+      // of the Itanium C++ ABI specification, it probably has to behave like
+      // the acquisition of a mutex, which needs an acquire fence.
+      atomic_thread_fence(memory_order_acquire);
+      return 1;
+    } else if (old_value == CONSTRUCTION_UNDERWAY_WITHOUT_WAITER) {
+      if (!atomic_compare_exchange_weak_explicit(
+              &gv->state, &old_value, CONSTRUCTION_UNDERWAY_WITH_WAITER,
+              memory_order_relaxed, memory_order_relaxed)) {
+        continue;
+      }
+    }
+    nsync_futex_wait_(&gv->state, CONSTRUCTION_UNDERWAY_WITH_WAITER, 0, 0);
+    old_value = atomic_load_explicit(&gv->state, memory_order_relaxed);
+  }
+}
+
+void __cxa_guard_release(union CxaGuardValue *gv) {
+  // Release fence is used to make all stores performed by the construction
+  // function visible in other threads.
+  int old_value = atomic_exchange_explicit(&gv->state, CONSTRUCTION_COMPLETE,
+                                           memory_order_release);
+  if (old_value == CONSTRUCTION_UNDERWAY_WITH_WAITER) {
+    nsync_futex_wake_(&gv->state, INT_MAX, 0);
+  }
+}
+
+void __cxa_guard_abort(union CxaGuardValue *gv) {
+  // Release fence is used to make all stores performed by the construction
+  // function visible in other threads.
+  int old_value = atomic_exchange_explicit(
+      &gv->state, CONSTRUCTION_NOT_YET_STARTED, memory_order_release);
+  if (old_value == CONSTRUCTION_UNDERWAY_WITH_WAITER) {
+    nsync_futex_wake_(&gv->state, INT_MAX, 0);
+  }
+}

libc/runtime/runtime.mk

@@ -45,6 +45,7 @@ LIBC_RUNTIME_A_DIRECTDEPS =				\
 	LIBC_STR					\
 	LIBC_SYSV					\
 	LIBC_SYSV_CALLS					\
+	THIRD_PARTY_NSYNC				\
 	THIRD_PARTY_PUFF				\
 	THIRD_PARTY_XED