Fix GetThreadContext stale register values use if WoW64 (Win32)

Issue #262 (bdwgc).

* misc.c [MSWIN32 && !MSWINRT_FLAVOR && !MSWIN_XBOX1]
(GC_win32_MessageBoxA): Do not define unless SMALL_CONFIG.
* misc.c [MSWIN32 && !_WIN64 && GC_WIN32_THREADS && CHECK_NOT_WOW64]
(GC_init): Do not call IsWow64Process() and GC_win32_MessageBoxA().
* win32_threads.c [I386] (isWow64): New static variable.
* win32_threads.c [I386] (GC_push_stack_for): If isWow64 then set also
CONTEXT_EXCEPTION_REQUEST and CONTEXT_SEGMENTS bits in ContextFlags;
if isWow64, and CONTEXT_EXCEPTION_REPORTING and
CONTEXT_EXCEPTION_ACTIVE are set on return from GetThreadContext then
call GetThreadSelectorEntry and use StackLimit of FS selector to set
sp local variable (instead of context.Esp); add comment.
* win32_threads.c [I386 && DEBUG_THREADS] (GC_push_stack_for): Call
GC_log_printf() to report TIB stack limit/base and the case when
CONTEXT_EXCEPTION_REQUEST is not supported.
* win32_threads.c [I386] (GC_thr_init): Set isWow64 by IsWow64Process()
if the later is available.

1 files changed, 1 insertions, 27 deletions

diff --git a/misc.c b/misc.c
index 7fb3abd1..4f3284ba 100644
--- a/misc.c
+++ b/misc.c
@@ -821,9 +821,7 @@ GC_API int GC_CALL GC_is_init_called(void)
 #endif
 
 #if defined(MSWIN32) && !defined(MSWINRT_FLAVOR) && !defined(MSWIN_XBOX1) \
-    && (!defined(SMALL_CONFIG) \
-        || (!defined(_WIN64) && defined(GC_WIN32_THREADS) \
-            && defined(CHECK_NOT_WOW64)))
+    && !defined(SMALL_CONFIG)
   STATIC void GC_win32_MessageBoxA(const char *msg, const char *caption,
                                    unsigned flags)
   {
@@ -929,30 +927,6 @@ GC_API void GC_CALL GC_init(void)
       initial_heap_sz = MINHINCR * HBLKSIZE;
 #   endif
 
-#   if defined(MSWIN32) && !defined(_WIN64) && defined(GC_WIN32_THREADS) \
-       && defined(CHECK_NOT_WOW64)
-      {
-        /* Windows: running 32-bit GC on 64-bit system is broken!       */
-        /* WoW64 bug affects SuspendThread, no workaround exists.       */
-        HMODULE hK32 = GetModuleHandle(TEXT("kernel32.dll"));
-        if (hK32) {
-          FARPROC pfn = GetProcAddress(hK32, "IsWow64Process");
-          BOOL bIsWow64 = FALSE;
-          if (pfn
-              && (*(BOOL (WINAPI*)(HANDLE, BOOL*))pfn)(GetCurrentProcess(),
-                                                       &bIsWow64)
-              && bIsWow64) {
-            GC_win32_MessageBoxA("This program uses BDWGC garbage collector"
-                " compiled for 32-bit but running on 64-bit Windows.\n"
-                "This is known to be broken due to a design flaw"
-                " in Windows itself! Expect erratic behavior...",
-                "32-bit program running on 64-bit system",
-                MB_ICONWARNING | MB_OK);
-          }
-        }
-      }
-#   endif
-
     DISABLE_CANCEL(cancel_state);
     /* Note that although we are nominally called with the */
     /* allocation lock held, the allocation lock is now    */