Adjust WoW64 workaround to work on UWP/WinRT

(cherry-pick of c511d4a from Unity-Technologies/bdwgc)

Dynamically lookup IsWow64Process2 and fallback to IsWow64Process if
needed.  Store TIB on each thread and lookup via call to NtCurrentTeb
on thread registration rather than calling GetThreadSelectorEntry
which is not available on UWP.

* include/private/pthread_support.h [WOW64_THREAD_CONTEXT_WORKAROUND
&& MSWINRT_FLAVOR] (GC_thread): Add tib field.
* win32_threads.c [WOW64_THREAD_CONTEXT_WORKAROUND && MSWINRT_FLAVOR]
(GC_register_my_thread_inner): Call NtCurrentTeb() and set tib field;
add comment.
* win32_threads.c [WOW64_THREAD_CONTEXT_WORKAROUND] (isWow64): Change
type from BOOL to GC_bool.
* win32_threads.c [WOW64_THREAD_CONTEXT_WORKAROUND]
(GC_push_stack_for): Define SegFs and selector local variables only
unless MSWINRT_FLAVOR; do not call GetThreadSelectorEntry() if
MSWINRT_FLAVOR.
* win32_threads.c [WOW64_THREAD_CONTEXT_WORKAROUND && MSWINRT_FLAVOR]
(GetModuleHandleW): Declare.
* win32_threads.c [WOW64_THREAD_CONTEXT_WORKAROUND] (is_wow64_process):
New static function (move part of code from GC_thr_init).
* win32_threads.c [WOW64_THREAD_CONTEXT_WORKAROUND && MSWINRT_FLAVOR]
(is_wow64_process): Call IsWow64Process2() dynamically; call
IsWow64Process() statically (if the previous one failed).
* win32_threads.c [WOW64_THREAD_CONTEXT_WORKAROUND] (GC_thr_init): Call
is_wow64_process().

Co-authored-by: Ivan Maidanski <ivmai@mail.ru>

1 files changed, 60 insertions, 17 deletions

diff --git a/win32_threads.c b/win32_threads.c
index ea22e888..1be559e5 100644
--- a/win32_threads.c
+++ b/win32_threads.c
@@ -257,6 +257,12 @@ GC_INNER GC_thread GC_register_my_thread_inner(const struct GC_stack_base *sb,
                    ": errcode= 0x%X", (unsigned)GetLastError());
     }
 # endif
+# if defined(WOW64_THREAD_CONTEXT_WORKAROUND) && defined(MSWINRT_FLAVOR)
+    /* Lookup TIB value via a call to NtCurrentTeb() on thread          */
+    /* registration rather than calling GetThreadSelectorEntry() which  */
+    /* is not available on UWP.                                         */
+    me -> tib = (PNT_TIB)NtCurrentTeb();
+# endif
   me -> crtn -> last_stack_min = ADDR_LIMIT;
   GC_record_stack_base(me -> crtn, sb);
   /* Up until this point, GC_push_all_stacks considers this thread      */
@@ -375,7 +381,7 @@ GC_INLINE LONG GC_get_max_thread_index(void)
 #   define CONTEXT_EXCEPTION_REQUEST   0x40000000
 #   define CONTEXT_EXCEPTION_REPORTING 0x80000000
 # endif
-  static BOOL isWow64;  /* Is running 32-bit code on Win64?     */
+  static GC_bool isWow64; /* Is running 32-bit code on Win64?   */
 # define GET_THREAD_CONTEXT_FLAGS (isWow64 \
                         ? CONTEXT_INTEGER | CONTEXT_CONTROL \
                           | CONTEXT_EXCEPTION_REQUEST | CONTEXT_SEGMENTS \
@@ -796,19 +802,25 @@ STATIC word GC_push_stack_for(GC_thread thread, thread_id_t self_id,
       /* WoW64 workaround. */
       if (isWow64) {
         DWORD ContextFlags = (DWORD)regs[0];
-        WORD SegFs = (WORD)regs[1];
 
         if ((ContextFlags & CONTEXT_EXCEPTION_REPORTING) != 0
             && (ContextFlags & (CONTEXT_EXCEPTION_ACTIVE
                                 /* | CONTEXT_SERVICE_ACTIVE */)) != 0) {
-          LDT_ENTRY selector;
           PNT_TIB tib;
 
-          if (!GetThreadSelectorEntry(THREAD_HANDLE(thread), SegFs, &selector))
-            ABORT("GetThreadSelectorEntry failed");
-          tib = (PNT_TIB)(selector.BaseLow
-                          | (selector.HighWord.Bits.BaseMid << 16)
-                          | (selector.HighWord.Bits.BaseHi << 24));
+#         ifdef MSWINRT_FLAVOR
+            tib = thread -> tib;
+#         else
+            WORD SegFs = (WORD)regs[1];
+            LDT_ENTRY selector;
+
+            if (!GetThreadSelectorEntry(THREAD_HANDLE(thread), SegFs,
+                                        &selector))
+              ABORT("GetThreadSelectorEntry failed");
+            tib = (PNT_TIB)(selector.BaseLow
+                            | (selector.HighWord.Bits.BaseMid << 16)
+                            | (selector.HighWord.Bits.BaseHi << 24));
+#         endif
 #         ifdef DEBUG_THREADS
             GC_log_printf("TIB stack limit/base: %p .. %p\n",
                           (void *)tib->StackLimit, (void *)tib->StackBase);
@@ -1566,6 +1578,45 @@ GC_API DECLSPEC_NORETURN void WINAPI GC_ExitThread(DWORD dwExitCode)
 
 #endif /* GC_WINMAIN_REDIRECT */
 
+#ifdef WOW64_THREAD_CONTEXT_WORKAROUND
+# ifdef MSWINRT_FLAVOR
+    /* Available on WinRT but we have to declare it manually.   */
+    __declspec(dllimport) HMODULE WINAPI GetModuleHandleW(LPCWSTR);
+# endif
+
+  static GC_bool is_wow64_process(HMODULE hK32)
+  {
+    BOOL is_wow64;
+#   ifdef MSWINRT_FLAVOR
+      /* Try to use IsWow64Process2 as it handles different WoW64 cases. */
+      HMODULE hWow64 = GetModuleHandleW(L"api-ms-win-core-wow64-l1-1-1.dll");
+
+      UNUSED_ARG(hK32);
+      if (hWow64) {
+        FARPROC pfn2 = GetProcAddress(hWow64, "IsWow64Process2");
+        USHORT process_machine, native_machine;
+
+        if (pfn2
+            && (*(BOOL (WINAPI*)(HANDLE, USHORT*, USHORT*))(word)pfn2)(
+                GetCurrentProcess(), &process_machine, &native_machine))
+          return process_machine != native_machine;
+      }
+      if (IsWow64Process(GetCurrentProcess(), &is_wow64))
+        return (GC_bool)is_wow64;
+#   else
+      if (hK32) {
+        FARPROC pfn = GetProcAddress(hK32, "IsWow64Process");
+
+        if (pfn
+            && (*(BOOL (WINAPI*)(HANDLE, BOOL*))(word)pfn)(
+                         GetCurrentProcess(), &is_wow64))
+          return (GC_bool)is_wow64;
+      }
+#   endif
+    return FALSE; /* IsWow64Process failed */
+  }
+#endif /* WOW64_THREAD_CONTEXT_WORKAROUND */
+
 GC_INNER void GC_thr_init(void)
 {
   struct GC_stack_base sb;
@@ -1597,18 +1648,10 @@ GC_INNER void GC_thr_init(void)
 # ifdef CAN_HANDLE_FORK
     GC_setup_atfork();
 # endif
-
 # ifdef WOW64_THREAD_CONTEXT_WORKAROUND
     /* Set isWow64 flag. */
-      if (hK32) {
-        FARPROC pfn = GetProcAddress(hK32, "IsWow64Process");
-        if (pfn
-            && !(*(BOOL (WINAPI*)(HANDLE, BOOL*))(word)pfn)(
-                                        GetCurrentProcess(), &isWow64))
-          isWow64 = FALSE; /* IsWow64Process failed */
-      }
+    isWow64 = is_wow64_process(hK32);
 # endif
-
   /* Add the initial thread, so we can stop it. */
   sb.mem_base = GC_stackbottom;
   GC_ASSERT(sb.mem_base != NULL);