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// GNU D Compiler emulated TLS routines.
// Copyright (C) 2019-2022 Free Software Foundation, Inc.
// GCC is free software; you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free
// Software Foundation; either version 3, or (at your option) any later
// version.
// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
// for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
// This code is based on the libgcc emutls.c emulated TLS support.
module gcc.emutls;
import core.atomic, core.stdc.stdlib, core.stdc.string, core.sync.mutex;
import core.internal.container.array;
import core.internal.container.hashtab;
import core.internal.traits : classInstanceAlignment;
import gcc.builtins, gcc.gthread;
version (GNU_EMUTLS): private:
alias word = __builtin_machine_uint;
alias pointer = __builtin_pointer_uint;
alias TlsArray = Array!(void**);
/*
* TLS control data emitted by GCC for every TLS variable.
*/
struct __emutls_object
{
word size;
word align_;
union
{
pointer offset;
void* ptr;
}
ubyte* templ;
}
// Per-thread key to obtain the per-thread TLS variable array
__gshared __gthread_key_t emutlsKey;
// Largest, currently assigned TLS variable offset
__gshared pointer emutlsMaxOffset = 0;
// Contains the size of the TLS variables (for GC)
__gshared Array!word emutlsSizes;
// Contains the TLS variable array for single-threaded apps
__gshared TlsArray singleArray;
// List of all currently alive TlsArrays (for GC)
__gshared HashTab!(TlsArray*, TlsArray*) emutlsArrays;
// emutlsMutex Mutex + @nogc handling
enum mutexAlign = classInstanceAlignment!Mutex;
enum mutexClassInstanceSize = __traits(classInstanceSize, Mutex);
__gshared align(mutexAlign) void[mutexClassInstanceSize] _emutlsMutex;
@property Mutex emutlsMutex() nothrow @nogc
{
return cast(Mutex) _emutlsMutex.ptr;
}
/*
* Global (de)initialization functions
*/
extern (C) void _d_emutls_init() nothrow @nogc
{
memcpy(_emutlsMutex.ptr, typeid(Mutex).initializer.ptr, _emutlsMutex.length);
(cast(Mutex) _emutlsMutex.ptr).__ctor();
if (__gthread_key_create(&emutlsKey, &emutlsDestroyThread) != 0)
abort();
}
__gshared __gthread_once_t initOnce = GTHREAD_ONCE_INIT;
/*
* emutls main entrypoint, called by GCC for each TLS variable access.
*/
extern (C) void* __emutls_get_address(shared __emutls_object* obj) nothrow @nogc
{
pointer offset;
if (__gthread_active_p())
{
// Obtain the offset index into the TLS array (same for all-threads)
// for requested var. If it is unset, obtain a new offset index.
offset = atomicLoad!(MemoryOrder.acq, pointer)(obj.offset);
if (__builtin_expect(offset == 0, 0))
{
__gthread_once(&initOnce, &_d_emutls_init);
emutlsMutex.lock_nothrow();
offset = obj.offset;
if (offset == 0)
{
offset = ++emutlsMaxOffset;
emutlsSizes.ensureLength(offset);
// Note: it's important that we copy any data from obj and
// do not keep an reference to obj itself: If a library is
// unloaded, its tls variables are not removed from the arrays
// and the GC will still scan these. If we then try to reference
// a pointer to the data segment of an unloaded library, this
// will crash.
emutlsSizes[offset - 1] = obj.size;
atomicStore!(MemoryOrder.rel, pointer)(obj.offset, offset);
}
emutlsMutex.unlock_nothrow();
}
}
// For single-threaded systems, don't synchronize
else
{
if (__builtin_expect(obj.offset == 0, 0))
{
offset = ++emutlsMaxOffset;
emutlsSizes.ensureLength(offset);
emutlsSizes[offset - 1] = obj.size;
obj.offset = offset;
}
}
TlsArray* arr;
if (__gthread_active_p())
arr = cast(TlsArray*) __gthread_getspecific(emutlsKey);
else
arr = &singleArray;
// This will always be false for singleArray
if (__builtin_expect(arr == null, 0))
{
arr = mallocTlsArray(offset);
__gthread_setspecific(emutlsKey, arr);
emutlsMutex.lock_nothrow();
emutlsArrays[arr] = arr;
emutlsMutex.unlock_nothrow();
}
// Check if we have to grow the per-thread array
else if (__builtin_expect(offset > arr.length, 0))
{
(*arr).ensureLength(offset);
}
// Offset 0 is used as a not-initialized marker above. In the
// TLS array, we start at 0.
auto index = offset - 1;
// Get the per-thread pointer from the TLS array
void** ret = (*arr)[index];
if (__builtin_expect(ret == null, 0))
{
// Initial access, have to allocate the storage
ret = emutlsAlloc(obj);
(*arr)[index] = ret;
}
return ret;
}
// 1:1 copy from libgcc emutls.c
extern (C) void __emutls_register_common(__emutls_object* obj, word size, word align_, ubyte* templ) nothrow @nogc
{
if (obj.size < size)
{
obj.size = size;
obj.templ = null;
}
if (obj.align_ < align_)
obj.align_ = align_;
if (templ && size == obj.size)
obj.templ = templ;
}
// 1:1 copy from libgcc emutls.c
void** emutlsAlloc(shared __emutls_object* obj) nothrow @nogc
{
void* ptr;
void* ret;
enum pointerSize = (void*).sizeof;
/* We could use here posix_memalign if available and adjust
emutls_destroy accordingly. */
if ((cast() obj).align_ <= pointerSize)
{
ptr = malloc((cast() obj).size + pointerSize);
if (ptr == null)
abort();
(cast(void**) ptr)[0] = ptr;
ret = ptr + pointerSize;
}
else
{
ptr = malloc(obj.size + pointerSize + obj.align_ - 1);
if (ptr == null)
abort();
ret = cast(void*)((cast(pointer)(ptr + pointerSize + obj.align_ - 1)) & ~cast(
pointer)(obj.align_ - 1));
(cast(void**) ret)[-1] = ptr;
}
if (obj.templ)
memcpy(ret, cast(ubyte*) obj.templ, cast() obj.size);
else
memset(ret, 0, cast() obj.size);
return cast(void**) ret;
}
/*
* When a thread has finished, free all allocated TLS variables and empty the
* array. The pointer is not free'd as it is stil referenced by the GC scan
* list emutlsArrays, which gets destroyed when druntime is unloaded.
*/
extern (C) void emutlsDestroyThread(void* ptr) nothrow @nogc
{
auto arr = cast(TlsArray*) ptr;
foreach (entry; *arr)
{
if (entry)
free(entry[-1]);
}
arr.length = 0;
}
/*
* Allocate a new TLS array, set length according to offset.
*/
TlsArray* mallocTlsArray(pointer offset = 0) nothrow @nogc
{
static assert(TlsArray.alignof == (void*).alignof);
void[] data = malloc(TlsArray.sizeof)[0 .. TlsArray.sizeof];
if (data.ptr == null)
abort();
static immutable TlsArray init = TlsArray.init;
memcpy(data.ptr, &init, data.length);
(cast(TlsArray*) data).length = 32;
return cast(TlsArray*) data.ptr;
}
/*
* Make sure array is large enough to hold an entry for offset.
* Note: the array index will be offset - 1!
*/
void ensureLength(Value)(ref Array!(Value) arr, size_t offset) nothrow @nogc
{
// index is offset-1
if (offset > arr.length)
{
auto newSize = arr.length * 2;
if (offset > newSize)
newSize = offset + 32;
arr.length = newSize;
}
}
// Public interface
public:
void _d_emutls_scan(scope void delegate(void* pbeg, void* pend) nothrow cb) nothrow
{
void scanArray(scope TlsArray* arr) nothrow
{
foreach (index, entry; *arr)
{
auto ptr = cast(void*) entry;
if (ptr)
cb(ptr, ptr + emutlsSizes[index]);
}
}
__gthread_once(&initOnce, &_d_emutls_init);
emutlsMutex.lock_nothrow();
// this code is effectively nothrow
try
{
foreach (arr, value; emutlsArrays)
{
scanArray(arr);
}
}
catch (Exception)
{
}
emutlsMutex.unlock_nothrow();
scanArray(&singleArray);
}
// Call this after druntime has been unloaded
void _d_emutls_destroy() nothrow @nogc
{
(cast(Mutex) _emutlsMutex.ptr).__dtor();
destroy(emutlsArrays);
}