/***
*tlsdyn.cpp - Thread Local Storage dynamic initialization run-time support module
*
*       Copyright (c) Microsoft Corporation. All rights reserved.
*
*Purpose:
*       Provide the TLS equivalent of DllMainCRTStartup, to be called by the
*       OS when a thread begins or ends.  On thread start, walk the list of
*       pointers to initialization routines for dynamically-initialized
*       __declspec(thread) variables.  On thread stop, walk the list of
*       destructors for __declspec(thread) variables, as registered at
*       initialization time.
*
****/

#ifdef MRTDLL
    #error This file is not built for the Managed CRT
#endif

#undef CRTDLL

#include <vcruntime_internal.h>
#include <eh.h>

extern "C" {

/*
 * Start and end sections for array of TLS callBacks to initialize individual
 * dynamically initialized __declspec(thread) items.  The actual array of
 * callbacks is constructed using .CRT$XDA, .CRT$XDC, .CRT$XDL, .CRT$XDU,
 * and .CRT$XDZ similar to the way global static initializers are done
 * for C++.  The C++ compiler will inject function pointers into .CRT$XD[CLU]
 * for each dynamically initialized __declspec(thread) variable, as well as
 * injecting a /include:__dyn_tls_init directive into the enclosing .obj,
 * to force inclusion of this support object.
 */

static _CRTALLOC(".CRT$XDA") _PVFV __xd_a = nullptr;

static _CRTALLOC(".CRT$XDZ") _PVFV __xd_z = nullptr;

/*
 * References to __tls_guard are generated by the compiler to detect if
 * dynamic initialization of TLS variables have run. This flag must be
 * set to 'true' before running the TLS initializers below.
 *
 * Note: [[msvc::no_tls_guard]] is not required here as it is known to
 * be statically initialized in this TU and all uses here will be unguarded
 * because of this. It is included for completion only but would be
 * necessary if a declaration is moved to a header and this variable
 * referenced from other files.
 */
[[msvc::no_tls_guard]] __declspec(thread) bool __tls_guard = false;

/*
 * __dyn_tls_init - dynamically initialize __declspec(thread) variables
 *
 * Purpose:
 *      When any thread starts up, walk the array of function pointers found
 *      in sections .CRT$XD*, calling each non-NULL entry to dynamically
 *      initialize that thread's copy of a __declspec(thread) variable.
 *
 * Entry:
 *      This is called directly from the Windows loader code, with dwReason
 *      equal to one of DLL_PROCESS_ATTACH/DETACH or DLL_THREAD_ATTACH_DETACH.
 *
 * Exit:
 *      Returns TRUE always, though the loader code ignores the result.
 *
 * Notes:
 *      Only calls the initializers on DLL_THREAD_ATTACH and not
 *      DLL_PROCESS_ATTACH.  That's because the DLL_PROCESS_ATTACH call happens
 *      too early, before the CRT has been initialized in, e.g.,
 *      DllMainCRTStartup or mainCRTStartup.  Instead, the CRT init code will
 *      call here directly with a DLL_THREAD_ATTACH to initialize any
 *      __declspec(thread) variables in the primary thread at process startup.
 */

void WINAPI __dyn_tls_init(PVOID, DWORD dwReason, LPVOID) noexcept // terminate on any C++ exception that leaves a
                                                                   // namespace-scope thread-local initializer
                                                                   // N4830 [basic.start.dynamic]/7
{
    if (dwReason != DLL_THREAD_ATTACH || __tls_guard == true)
        return;

    /*
     * Guard against repeated initialization by setting the tls guard tested
     * by the compiler before we run any initializers.
     */
    __tls_guard = true;

    /* prefast assumes we are overflowing __xd_a */
    #pragma warning(push)
    #pragma warning(disable: 26000)
    for (_PVFV* pfunc = &__xd_a + 1; pfunc != &__xd_z; ++pfunc)
    {
        if (*pfunc)
            (*pfunc)();
    }
    #pragma warning(pop)
}

#ifdef _M_ARM64EC
#pragma comment (linker, "-arm64xsameaddress:__dyn_tls_init")
#endif

/*
 * Define an initialized callback function pointer, so CRT startup code knows
 * we have dynamically initialized __declspec(thread) variables that need to
 * be initialized at process startup for the primary thread.
 */

extern const PIMAGE_TLS_CALLBACK __dyn_tls_init_callback = __dyn_tls_init;

/*
 * Enter a callback function pointer into the .CRT$XL* array, which is the
 * callback array pointed to by the IMAGE_TLS_DIRECTORY in the PE header, so
 * the OS knows we want to be notified on each thread startup/shutdown.
 */

static _CRTALLOC(".CRT$XLC") PIMAGE_TLS_CALLBACK __xl_c = __dyn_tls_init;

/*
 * Helper function invoked by the compiler for on-demand initialization of
 * TLS variables when the initializers have not run because a DLL is dynamically
 * loaded after the thread(s) have started.
 */
void __cdecl __dyn_tls_on_demand_init() noexcept
{
    __dyn_tls_init(nullptr, DLL_THREAD_ATTACH, nullptr);
}

extern ULONG _tls_index;

/*
 * This function is exported from a DLL that exports at least one TLS variable.
 * It ensures that the TLS variables on this thread are initialized before returning
 * the _tls_index.
 */
unsigned long __cdecl __safe_get_tls_index() noexcept
{
    __dyn_tls_on_demand_init();

    return _tls_index;
}

} // extern "C"