From f81c82f5fa68177c6707aa2f52cd2dda9a4b3916 Mon Sep 17 00:00:00 2001
From: Timo Kreuzer <timo.kreuzer@reactos.org>
Date: Sun, 9 Feb 2025 12:46:03 +0200
Subject: [PATCH] [VCSTARTUP] Implement atexit and _onexit

These must use a local table and cannot use the one from ucrtbase.
The table is initialized with a .CRT section initializer.
---
 sdk/lib/vcruntime/CMakeLists.txt        |  2 ++
 sdk/lib/vcruntime/_onexit.c             | 34 +++++++++++++++++++++++++
 sdk/lib/vcruntime/atexit.c              | 18 +++++++++++++
 sdk/lib/vcruntime/inc/internal_shared.h |  1 +
 4 files changed, 55 insertions(+)
 create mode 100644 sdk/lib/vcruntime/_onexit.c
 create mode 100644 sdk/lib/vcruntime/atexit.c

diff --git a/sdk/lib/vcruntime/CMakeLists.txt b/sdk/lib/vcruntime/CMakeLists.txt
index 405dc705bd9..6851dcaef0b 100644
--- a/sdk/lib/vcruntime/CMakeLists.txt
+++ b/sdk/lib/vcruntime/CMakeLists.txt
@@ -35,6 +35,8 @@ list(APPEND VCRT_STARTUP_SOURCES
     __acrt_initialize_stub.cpp
     __scrt_uninitialize_crt.cpp
     __vcrt_init_stubs.c
+    _onexit.c
+    atexit.c
     mainCRTStartup.cpp
     wmainCRTStartup.cpp
 )
diff --git a/sdk/lib/vcruntime/_onexit.c b/sdk/lib/vcruntime/_onexit.c
new file mode 100644
index 00000000000..3d3572c3bf2
--- /dev/null
+++ b/sdk/lib/vcruntime/_onexit.c
@@ -0,0 +1,34 @@
+//
+// _onexit.c
+//
+//      Copyright (c) 2024 Timo Kreuzer
+//
+// Implementation of _onexit.
+//
+// SPDX-License-Identifier: MIT
+//
+
+#include <stdlib.h>
+#include <internal_shared.h>
+#include <corecrt_startup.h>
+#include <assert.h>
+
+_onexit_table_t module_local_atexit_table;
+int module_local_atexit_table_initialized = 0;
+
+int __cdecl __scrt_initialize_onexit(void)
+{
+    _initialize_onexit_table(&module_local_atexit_table);
+    module_local_atexit_table_initialized = 1;
+    return 0;
+}
+
+// CRT startup initializer
+_CRTALLOC(".CRT$XIAA") _PIFV const __scrt_onexit_initializer = __scrt_initialize_onexit;
+
+_onexit_t __cdecl _onexit(_In_opt_ _onexit_t _Func)
+{
+    assert(module_local_atexit_table_initialized == 1);
+    int result = _register_onexit_function(&module_local_atexit_table, _Func);
+    return (result == 0) ? _Func : NULL;
+}
diff --git a/sdk/lib/vcruntime/atexit.c b/sdk/lib/vcruntime/atexit.c
new file mode 100644
index 00000000000..391e416bb82
--- /dev/null
+++ b/sdk/lib/vcruntime/atexit.c
@@ -0,0 +1,18 @@
+//
+// atexit.c
+//
+//      Copyright (c) 2024 Timo Kreuzer
+//
+// Implementation of atexit.
+//
+// SPDX-License-Identifier: MIT
+//
+
+#include <stdlib.h>
+
+int __cdecl atexit(void (__cdecl* _Func)(void))
+{
+    // Go through _onexit, so that the initializer is pulled in.
+    _onexit_t result = _onexit((_onexit_t)_Func);
+    return (result == NULL) ? -1 : 0;
+}
diff --git a/sdk/lib/vcruntime/inc/internal_shared.h b/sdk/lib/vcruntime/inc/internal_shared.h
index 968f5ecb498..b3274a030d9 100644
--- a/sdk/lib/vcruntime/inc/internal_shared.h
+++ b/sdk/lib/vcruntime/inc/internal_shared.h
@@ -31,6 +31,7 @@ extern "C" {
 #pragma section(".CRT$XPXA", long, read)
 
 #pragma section(".CRT$XIA", long, read)
+#pragma section(".CRT$XIAA", long, read) // CRT startup
 #pragma section(".CRT$XIZ", long, read)
 #pragma section(".CRT$XCA", long, read)
 #pragma section(".CRT$XCZ", long, read)