Reland: [wasm] Check correctness of thread-local write protection

The fix landed as a separate CL: https://crrev.com/c/3081522
This is an unmodified reland.

Original description:
We make an undocumented assumption in {CodeSpaceWriteScope} that a
single thread will only work on one module at a time. If this is
violated, the thread-local {code_space_write_nesting_level_} would
prevent the second module from being switched to writable.

This CL adds a second thread local (in debug only) to check that if
there is already a {CodeSpaceWriteScope} open that it contains the same
{NativeModule} as any nested scope.

R=jkummerow@chromium.org

Bug: v8:11974
Cq-Include-Trybots: luci.v8.try:v8_linux_gc_stress_dbg_ng
Cq-Include-Trybots: luci.v8.try:v8_mac64_gc_stress_dbg_ng
Change-Id: Id827b6ca472f695e4500584349aba159aa07eed1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3080578
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76177}

src/wasm/code-space-access.cc

@@ -12,6 +12,12 @@ namespace internal {
 namespace wasm {
 
 thread_local int CodeSpaceWriteScope::code_space_write_nesting_level_ = 0;
+// The thread-local counter (above) is only valid if a single thread only works
+// on one module at a time. This second thread-local checks that.
+#if defined(DEBUG) && (!defined(V8_OS_MACOSX) || !defined(V8_HOST_ARCH_ARM64))
+thread_local NativeModule* CodeSpaceWriteScope::current_native_module_ =
+    nullptr;
+#endif
 
 // TODO(jkummerow): Background threads could permanently stay in
 // writable mode; only the main thread has to switch back and forth.
@@ -20,6 +26,12 @@ CodeSpaceWriteScope::CodeSpaceWriteScope(NativeModule*) {
 #else  // !V8_HAS_PTHREAD_JIT_WRITE_PROTECT
 CodeSpaceWriteScope::CodeSpaceWriteScope(NativeModule* native_module)
     : native_module_(native_module) {
+#ifdef DEBUG
+  if (code_space_write_nesting_level_ == 0) {
+    current_native_module_ = native_module;
+  }
+  DCHECK_EQ(native_module, current_native_module_);
+#endif  // DEBUG
 #endif  // !V8_HAS_PTHREAD_JIT_WRITE_PROTECT
   if (code_space_write_nesting_level_ == 0) SetWritable();
   code_space_write_nesting_level_++;

src/wasm/code-space-access.h

@@ -55,6 +55,9 @@ class V8_NODISCARD CodeSpaceWriteScope final {
 
  private:
   static thread_local int code_space_write_nesting_level_;
+#if defined(DEBUG) && (!defined(V8_OS_MACOSX) || !defined(V8_HOST_ARCH_ARM64))
+  static thread_local NativeModule* current_native_module_;
+#endif
 
   void SetWritable() const;
   void SetExecutable() const;