Reverted r35812 because of unwanted triple fault bug.

[reactos.git] / reactos / dll / ntdll / dispatch / i386 / dispatch.S

diff --git a/reactos/dll/ntdll/dispatch/i386/dispatch.S b/reactos/dll/ntdll/dispatch/i386/dispatch.S
index 00a21f4..526e5b8 100644 (file)
--- a/reactos/dll/ntdll/dispatch/i386/dispatch.S
+++ b/reactos/dll/ntdll/dispatch/i386/dispatch.S
@@ -183,13 +183,43 @@ _KiRaiseUserExceptionDispatcher@0:
 .globl _KiUserExceptionDispatcher@8\r
 _KiUserExceptionDispatcher@8:\r
 \r
-    /* Clear direction flag */\r
+    /* clear the direct flag \r
+     * text from bug 2279\r
+     * if it not clear it means that if an exception occurs while\r
+     * the direction flag is set (typically inside memmove), the \r
+     * exception handlers will be called with the direction flag still\r
+     * set.  The Windows x86-32 and x86-64 ABI requires that the \r
+     * direction flag be Calling memset() with a compile-time constant \r
+     * size on both GCC and MSVC will result in inlining a "rep stosd" \r
+     * instruction.  Because of the ABI, they will assume that the \r
+     * direction flag is clear and not emit a "cld" instruction. \r
+     * Using memset() in an exception handler therefore will \r
+     * corrupt memory if the exception occurred during a reverse copy \r
+     * such as a forward overlapping memmove().\r
+     *\r
+     * For reliability and ease of debugging, please add "cld" to the beginning of\r
+     * KiUserExceptionDispatcher.  Note that the same will be true of x86-64 whenever\r
+     * that happens.  This does not affect continuing execution; the CONTEXT of the\r
+     * exception has the direction flag set and will be restored upon NtContinue. \r
+     * KiUserApcDispatcher and KiUserCallbackDispatcher need to be evaluated for this\r
+     * issue.\r
+     */\r
+     \r
     cld\r
 \r
     /* Save the Context and Exception Records */\r
     mov ecx, [esp+4]\r
     mov ebx, [esp]\r
 \r
+    /* Call the vectored exception handler */\r
+    push ecx\r
+    push ebx\r
+    call _RtlpExecuteVectoredExceptionHandlers@8\r
+\r
+    /* Check for success */\r
+    or al, al\r
+    jnz ContinueExecution\r
+\r
     /* Dispatch the exception */\r
     sub esp, 8\r
     call _RtlDispatchException@8\r
@@ -198,6 +228,7 @@ _KiUserExceptionDispatcher@8:
     or al, al\r
     jz RaiseException\r
 \r
+ContinueExecution:\r
     /* Pop off the records */\r
     pop ebx\r
     pop ecx\r