1 files changed, 132 insertions, 0 deletions
diff --git a/js/src/jit/FlushICache.cpp b/js/src/jit/FlushICache.cpp
new file mode 100644
index 0000000000..1e2ec69272
--- /dev/null
+++ b/js/src/jit/FlushICache.cpp
@@ -0,0 +1,132 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "jit/FlushICache.h"
+
+#ifdef JS_CODEGEN_ARM64
+#  include "jit/arm64/vixl/MozCachingDecoder.h"
+#  include "jit/arm64/vixl/Simulator-vixl.h"
+#endif
+
+#if defined(JS_CODEGEN_ARM) || defined(JS_CODEGEN_ARM64)
+
+#  ifdef __linux__
+#    include <linux/version.h>
+#    define LINUX_HAS_MEMBARRIER (LINUX_VERSION_CODE >= KERNEL_VERSION(4, 3, 0))
+#  else
+#    define LINUX_HAS_MEMBARRIER 0
+#  endif
+
+#  if LINUX_HAS_MEMBARRIER || defined(__android__)
+#    include <string.h>
+
+#    if LINUX_HAS_MEMBARRIER
+#      include <linux/membarrier.h>
+#      include <sys/syscall.h>
+#      include <sys/utsname.h>
+#      include <unistd.h>
+#    elif defined(__android__)
+#      include <sys/syscall.h>
+#      include <unistd.h>
+#    else
+#      error "Missing platform-specific declarations for membarrier syscall!"
+#    endif  // __linux__ / ANDROID
+
+static int membarrier(int cmd, int flags) {
+  return syscall(__NR_membarrier, cmd, flags);
+}
+
+// These definitions come from the Linux kernel source, for kernels before 4.16
+// which didn't have access to these membarrier commands.
+#    ifndef MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE
+#      define MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE (1 << 5)
+#    endif
+
+#    ifndef MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE
+#      define MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE (1 << 6)
+#    endif
+#  endif  // LINUX_HAS_MEMBARRIER || defined(__android__)
+
+using namespace js;
+using namespace js::jit;
+
+namespace js {
+namespace jit {
+
+bool CanFlushExecutionContextForAllThreads() {
+#  if (LINUX_HAS_MEMBARRIER || defined(__android__))
+  // On linux, check the kernel supports membarrier(2), that is, it's a kernel
+  // above Linux 4.16 included.
+  //
+  // Note: this code has been extracted (August 2020) from
+  // https://android.googlesource.com/platform/art/+/58520dfba31d6eeef75f5babff15e09aa28e5db8/libartbase/base/membarrier.cc#50
+  static constexpr int kRequiredMajor = 4;
+  static constexpr int kRequiredMinor = 16;
+
+  static bool computed = false;
+  static bool kernelHasMembarrier = false;
+
+  if (computed) {
+    return kernelHasMembarrier;
+  }
+
+  struct utsname uts;
+  int major, minor;
+  kernelHasMembarrier = uname(&uts) == 0 && strcmp(uts.sysname, "Linux") == 0 &&
+                        sscanf(uts.release, "%d.%d", &major, &minor) == 2 &&
+                        major >= kRequiredMajor &&
+                        (major != kRequiredMajor || minor >= kRequiredMinor);
+
+  // As a test bed, try to run the syscall with the command registering the
+  // intent to use the actual membarrier we'll want to carry out later.
+  //
+  // IMPORTANT: This is required or else running the membarrier later won't
+  // actually interrupt the threads in this process.
+  if (kernelHasMembarrier &&
+      membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE, 0) != 0) {
+    kernelHasMembarrier = false;
+  }
+
+  computed = true;
+  return kernelHasMembarrier;
+#  else
+  // On other platforms, we assume that the syscall for flushing the icache
+  // will flush the execution context for other cores.
+  return true;
+#  endif
+}
+
+void FlushExecutionContextForAllThreads() {
+  // Callers must check that this operation is available.
+  MOZ_RELEASE_ASSERT(CanFlushExecutionContextForAllThreads());
+
+#  if defined(JS_SIMULATOR_ARM64) && defined(JS_CACHE_SIMULATOR_ARM64)
+  // Emulate what the real hardware would do by emitting a membarrier that'll
+  // interrupt and flush the execution context of all threads.
+  using js::jit::SimulatorProcess;
+  js::jit::AutoLockSimulatorCache alsc;
+  SimulatorProcess::membarrier();
+#  elif (LINUX_HAS_MEMBARRIER || defined(__android__))
+  // The caller has checked this can be performed, which will have registered
+  // this process to receive the membarrier. See above.
+  //
+  // membarrier will trigger an inter-processor-interrupt on any active threads
+  // of this process. This is an execution context synchronization event
+  // equivalent to running an `isb` instruction.
+  if (membarrier(MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE, 0) != 0) {
+    // Better safe than sorry.
+    MOZ_CRASH("membarrier can't be executed");
+  }
+#  else
+  // On other platforms, we assume that the syscall for flushing the icache
+  // will flush the execution context for other cores.
+#  endif
+}
+
+}  // namespace jit
+}  // namespace js
+
+#endif