[PATCH] ntdll: Ensure CONTEXT_EX on exception stack is initialized.

[Brendan Shanks]

On non-AVX CPUs, CONTEXT_EX is not being initialized.
In WOW64 mode, this results in invalid exception records when
dispatch_wow_exception() uses RtlCopyContext().

Signed-off-by: Brendan Shanks <bshanks(a)codeweavers.com>
---

- The XState/All lengths come from RtlInitializeExtendedContext2().
- I only experienced the bug on x86_64, but made the i386 change for
  consistency.

 dlls/ntdll/unix/signal_i386.c   | 23 +++++++++++++++++++----
 dlls/ntdll/unix/signal_x86_64.c | 23 +++++++++++++++++++----
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/dlls/ntdll/unix/signal_i386.c b/dlls/ntdll/unix/signal_i386.c
index 6bb5649e2b5..e2a6148d609 100644
--- a/dlls/ntdll/unix/signal_i386.c
+++ b/dlls/ntdll/unix/signal_i386.c
@@ -581,12 +581,23 @@ static inline void context_init_xstate( CONTEXT *context, void *xstate_buffer )
     xctx->Legacy.Length = sizeof(CONTEXT);
     xctx->Legacy.Offset = -(LONG)sizeof(CONTEXT);
 
-    xctx->XState.Length = sizeof(XSTATE);
-    xctx->XState.Offset = (BYTE *)xstate_buffer - (BYTE *)xctx;
+    if (xstate_buffer)
+    {
+        xctx->XState.Length = sizeof(XSTATE);
+        xctx->XState.Offset = (BYTE *)xstate_buffer - (BYTE *)xctx;
+        context->ContextFlags |= CONTEXT_XSTATE;
+
+        xctx->All.Length = sizeof(CONTEXT) + xctx->XState.Offset + xctx->XState.Length;
+    }
+    else
+    {
+        xctx->XState.Length = 25;
+        xctx->XState.Offset = 0;
+
+        xctx->All.Length = sizeof(CONTEXT) + 24; /* sizeof(CONTEXT_EX) minus 8 alignment bytes on x64. */
+    }
 
-    xctx->All.Length = sizeof(CONTEXT) + xctx->XState.Offset + xctx->XState.Length;
     xctx->All.Offset = -(LONG)sizeof(CONTEXT);
-    context->ContextFlags |= CONTEXT_XSTATE;
 }
 
 
@@ -1456,6 +1467,10 @@ C_ASSERT( (offsetof(struct stack_layout, xstate) == sizeof(struct stack_layout))
             memcpy( &dst_xs->YmmContext, &src_xs->YmmContext, sizeof(dst_xs->YmmContext) );
         }
     }
+    else
+    {
+        context_init_xstate( &stack->context, NULL );
+    }
 
     stack->rec_ptr      = &stack->rec;
     stack->context_ptr  = &stack->context;
diff --git a/dlls/ntdll/unix/signal_x86_64.c b/dlls/ntdll/unix/signal_x86_64.c
index ac67e12240a..29096261723 100644
--- a/dlls/ntdll/unix/signal_x86_64.c
+++ b/dlls/ntdll/unix/signal_x86_64.c
@@ -413,12 +413,23 @@ static inline void context_init_xstate( CONTEXT *context, void *xstate_buffer )
     xctx->Legacy.Length = sizeof(CONTEXT);
     xctx->Legacy.Offset = -(LONG)sizeof(CONTEXT);
 
-    xctx->XState.Length = sizeof(XSTATE);
-    xctx->XState.Offset = (BYTE *)xstate_buffer - (BYTE *)xctx;
+    if (xstate_buffer)
+    {
+        xctx->XState.Length = sizeof(XSTATE);
+        xctx->XState.Offset = (BYTE *)xstate_buffer - (BYTE *)xctx;
+        context->ContextFlags |= CONTEXT_XSTATE;
+
+        xctx->All.Length = sizeof(CONTEXT) + xctx->XState.Offset + xctx->XState.Length;
+    }
+    else
+    {
+        xctx->XState.Length = 25;
+        xctx->XState.Offset = 0;
+
+        xctx->All.Length = sizeof(CONTEXT) + 24; /* sizeof(CONTEXT_EX) minus 8 alignment bytes on x64. */
+    }
 
-    xctx->All.Length = sizeof(CONTEXT) + xctx->XState.Offset + xctx->XState.Length;
     xctx->All.Offset = -(LONG)sizeof(CONTEXT);
-    context->ContextFlags |= CONTEXT_XSTATE;
 }
 
 static USHORT cs32_sel;  /* selector for %cs in 32-bit mode */
@@ -2198,6 +2209,10 @@ static void setup_raise_exception( ucontext_t *sigcontext, EXCEPTION_RECORD *rec
             memcpy( &dst_xs->YmmContext, &src_xs->YmmContext, sizeof(dst_xs->YmmContext) );
         }
     }
+    else
+    {
+        context_init_xstate( &stack->context, NULL );
+    }
 
     CS_sig(sigcontext)  = cs64_sel;
     RIP_sig(sigcontext) = (ULONG_PTR)pKiUserExceptionDispatcher;
-- 
2.32.0 (Apple Git-132)