Bug 15976 – explicite TLS initializes badly in DLLs if other threads exist

This happened for intermediate versions of druntime that used explicite TLS to save the thread pointer: This is the DLL code: ///////////////////////////////////////////// module exptls; import core.sys.windows.windows; import core.sys.windows.dll; import core.stdc.stdio; mixin SimpleDllMain; __gshared DWORD tlsSlot; int tlsVar; shared static this() { tlsSlot = TlsAlloc(); printf("TlsAlloc() = %d\n", tlsSlot); } static this() { printf("TlsSetValue(%d, &var = %p\n", tlsSlot, &tlsVar); TlsSetValue(tlsSlot, &tlsVar); } And the executable: //////////////////////////////////////////////////// module main; import core.sys.windows.windows; import core.thread; import core.time; alias fnType = void function(); __gshared fnType pFn; void test() { Thread.sleep(2.seconds); assert(pFn); pFn(); } void main() { Thread t1 = new Thread(&test); t1.start(); Thread.sleep(1.seconds); HANDLE h = LoadLibrary("exptls.dll"); pFn = cast(fnType) GetProcAddress(h, "verifyTls"); assert(pFn); pFn(); t1.join(); } extern(C) export void verifyTls() { printf("TlsGetValue() = %x, &var = %x\n", TlsGetValue(tlsSlot), &tlsVar); assert(TlsGetValue(tlsSlot) == &tlsVar); } Compile with: dmd -ofexptls.dll exptls.d -m64 -L/DLL dmd main.d -m64 Running produces output similar to: TlsAlloc() = 26 TlsSetValue(26, &var = 0000005FF88E3B50 TlsSetValue(26, &var = 0000005FF88F36B0 TlsGetValue() = f88f36b0, &var = f88e3b50 and the process crashes (due to the assert exception from DLL not being handled).

This happens because the "impersonation" of existing threads during DLL startup does not swap explicit TLS values, only implicit.

Commits pushed to master at https://github.com/dlang/druntime https://github.com/dlang/druntime/commit/998c0fc455c959bfb55c1a26ef8b9599622bc457 fix issue 15976: swap out explicit TLS values during impersonating thread https://github.com/dlang/druntime/commit/c7ddfef05d0d6ed564aecd2e6a51b6e6a93f689a Merge pull request #1556 from rainers/explicit_tls fix issue 15976: swap out explicit TLS values during impersonating thread

Commits pushed to stable at https://github.com/dlang/druntime https://github.com/dlang/druntime/commit/998c0fc455c959bfb55c1a26ef8b9599622bc457 fix issue 15976: swap out explicit TLS values during impersonating thread https://github.com/dlang/druntime/commit/c7ddfef05d0d6ed564aecd2e6a51b6e6a93f689a Merge pull request #1556 from rainers/explicit_tls