From 80cefb63b4e007cc8a2ad96af5a7a45a6b87b7af Mon Sep 17 00:00:00 2001
From: Timo Kreuzer <timo.kreuzer@reactos.org>
Date: Tue, 17 Jun 2025 21:28:09 +0300
Subject: [PATCH] [MSVCRT_SHARED] Implement TLS support for ucrtbase

---
 dll/win32/msvcrt/CMakeLists.txt         |  1 +
 dll/win32/msvcrt/reactos/ucrt_tls_sup.c | 81 +++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 dll/win32/msvcrt/reactos/ucrt_tls_sup.c

diff --git a/dll/win32/msvcrt/CMakeLists.txt b/dll/win32/msvcrt/CMakeLists.txt
index 4d389ee5543..7028798e734 100644
--- a/dll/win32/msvcrt/CMakeLists.txt
+++ b/dll/win32/msvcrt/CMakeLists.txt
@@ -115,6 +115,7 @@ add_asm_files(msvcrt_shared_asm ${SHARED_ASM_SOURCE})
 add_library(msvcrt_shared
     ${SHARED_SOURCE}
     ${msvcrt_shared_asm}
+    reactos/ucrt_tls_sup.c
 )
 
 target_compile_definitions(msvcrt_shared PRIVATE _MSVCR_VER=0 __UCRTSUPPORT__)
diff --git a/dll/win32/msvcrt/reactos/ucrt_tls_sup.c b/dll/win32/msvcrt/reactos/ucrt_tls_sup.c
new file mode 100644
index 00000000000..c750f1f6bb3
--- /dev/null
+++ b/dll/win32/msvcrt/reactos/ucrt_tls_sup.c
@@ -0,0 +1,81 @@
+/*
+ * PROJECT:     ReactOS msvcrt
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     TLS support code for use with ucrtbase
+ * COPYRIGHT:   Copyright 2025 Timo Kreuzer <timo.kreuzer@reactos.org>
+ */
+
+#include <process.h>
+#include <assert.h>
+#include "msvcrt.h"
+#include "wine/debug.h"
+
+WINE_DEFAULT_DEBUG_CHANNEL(msvcrt);
+
+DWORD msvcrt_tls_index;
+
+BOOL msvcrt_init_tls(void)
+{
+    msvcrt_tls_index = TlsAlloc();
+    if (msvcrt_tls_index == TLS_OUT_OF_INDEXES)
+    {
+        ERR("TlsAlloc() failed!\n");
+        return FALSE;
+    }
+
+    return TRUE;
+}
+
+BOOL msvcrt_free_tls(void)
+{
+    if (!TlsFree(msvcrt_tls_index))
+    {
+        ERR("TlsFree() failed!\n");
+        return FALSE;
+    }
+
+    return TRUE;
+}
+
+void msvcrt_free_tls_mem(void)
+{
+    thread_data_t *tls = TlsGetValue(msvcrt_tls_index);
+    if (tls)
+    {
+        free(tls->efcvt_buffer);
+        assert(tls->asctime_buffer == NULL);
+        assert(tls->wasctime_buffer == NULL);
+        assert(tls->strerror_buffer == NULL);
+        assert(tls->wcserror_buffer == NULL);
+        assert(tls->time_buffer == NULL);
+        assert(tls->tmpnam_buffer == NULL);
+        assert(tls->wtmpnam_buffer == NULL);
+        assert(tls->locinfo == NULL);
+        assert(tls->mbcinfo == NULL);
+        HeapFree(GetProcessHeap(), 0, tls);
+    }
+}
+
+thread_data_t *CDECL msvcrt_get_thread_data(void)
+{
+    thread_data_t *ptr;
+    DWORD err = GetLastError();  /* need to preserve last error */
+
+    ptr = TlsGetValue(msvcrt_tls_index);
+    if (ptr == NULL)
+    {
+        ptr = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(*ptr));
+        if (ptr == NULL)
+            exit(_RT_THREAD);
+
+        if (!TlsSetValue(msvcrt_tls_index, ptr))
+            exit(_RT_THREAD);
+
+        ptr->tid = GetCurrentThreadId();
+        ptr->handle = INVALID_HANDLE_VALUE;
+        ptr->random_seed = 1;
+    }
+
+    SetLastError(err);
+    return ptr;
+}