[PATCH] ntdll: Implement NtGetCurrentProcessorNumber() for Mac OS.

[Chip Davis]

Signed-off-by: Chip Davis <cdavis5x at gmail.com>
---
 dlls/ntdll/unix/thread.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/dlls/ntdll/unix/thread.c b/dlls/ntdll/unix/thread.c
index 451402159d46..3e9e4d740e6a 100644
--- a/dlls/ntdll/unix/thread.c
+++ b/dlls/ntdll/unix/thread.c
@@ -2285,6 +2285,21 @@ ULONG WINAPI NtGetCurrentProcessorNumber(void)
     if (res != -1) return processor;
 #endif
 
+#if defined(__APPLE__) && (defined(__i386__) || defined(__x86_64__))
+    /* A little known feature of macOS is that it will stash the CPU number
+     * in the low 12 bits of the IDTR's limit field.
+     */
+#include "pshpack1.h"
+    struct
+    {
+        USHORT limit;
+        ULONG_PTR base;
+    } idtr;
+#include "poppack.h"
+    asm("sidt %0" : "=m" (idtr));
+    return idtr.limit & 0xfff;
+#endif
+
     if (peb->NumberOfProcessors > 1)
     {
         ULONG_PTR thread_mask, processor_mask;
-- 
2.34.1