LibC: Support exit time destructors per the Itanium C++ ABI

Implement __cxa_atexit and __cxa_finalize per the Itanium spec,
and convert stdlib's atexit and exit() to to call them instead of
a custom 'C-only' atexit implementation.

1 files changed, 42 insertions, 1 deletions

diff --git a/Libraries/LibC/crt0.cpp b/Libraries/LibC/crt0.cpp
index d8f6da41ef..90f57b75ed 100644
--- a/Libraries/LibC/crt0.cpp
+++ b/Libraries/LibC/crt0.cpp
@@ -49,8 +49,49 @@ int _start(int argc, char** argv, char** env)
     ASSERT_NOT_REACHED();
 }
 
-void __cxa_atexit()
+typedef void (*AtExitFunction)(void *);
+
+struct __exit_entry
+{
+    AtExitFunction method;
+    void* parameter;
+    void* dso_handle;
+    bool has_been_called;
+};
+
+static __exit_entry __exit_entries[1024]{};
+static int __exit_entry_count = 0;
+
+int __cxa_atexit(AtExitFunction exit_function, void *parameter, void *dso_handle)
+{
+    if (__exit_entry_count >= 1024)
+        return -1;
+
+    __exit_entries[__exit_entry_count++] = { exit_function, parameter, dso_handle, false};
+
+    return 0;
+}
+
+void __cxa_finalize(void* dso_handle)
 {
+    // From the itanium abi, https://itanium-cxx-abi.github.io/cxx-abi/abi.html#dso-dtor-runtime-api
+    //
+    // When __cxa_finalize(d) is called, it should walk the termination function list, calling each in turn
+    // if d matches __dso_handle for the termination function entry. If d == NULL, it should call all of them.
+    // Multiple calls to __cxa_finalize shall not result in calling termination function entries multiple times;
+    // the implementation may either remove entries or mark them finished.
+
+    int entry_index = __exit_entry_count;
+
+    while (--entry_index >= 0)
+    {
+        auto& exit_entry = __exit_entries[entry_index];
+        bool needs_calling = !exit_entry.has_been_called && (!dso_handle || dso_handle == exit_entry.dso_handle);
+        if (needs_calling) {
+            exit_entry.method(exit_entry.parameter);
+            exit_entry.has_been_called = true;
+        }
+    }
 }
 
 extern u32 __stack_chk_guard;