[PATCH 2/4] ntdll/tests: Fix incorrect calculation of context length in test_copy_context().

[Jinoh Kang]

From: Jinoh Kang

`(BYTE *)dst_ex - (BYTE *)dst` is the size of the legacy context, but
`dst_ex->All` already contains the legacy context.  Therefore,
`context_length` has the legacy context size added *twice*.

This becomes a problem when `context_length` exceeds
`sizeof(src_context_buffer)`.  This confuses `check_changes_in_range()`,
causing out-of-bounds read and unpredictable test results.
---
 dlls/ntdll/tests/exception.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/ntdll/tests/exception.c b/dlls/ntdll/tests/exception.c
index 79a65dadab9..9f6bfbd2008 100644
--- a/dlls/ntdll/tests/exception.c
+++ b/dlls/ntdll/tests/exception.c
@@ -11952,7 +11952,7 @@ static void test_copy_context(void)
         *(DWORD *)((BYTE *)dst + flags_offset) = 0;
         *(DWORD *)((BYTE *)src + flags_offset) = 0;

-        context_length = (BYTE *)dst_ex - (BYTE *)dst + dst_ex->All.Length;
+        context_length = dst_ex->All.Length;

if (flags & 0x40)
         {