ntdll: In SYSTEM_BASIC_INFORMATION, the active processors field refers to the affinity mask.

dlls/kernel32/cpu.c

@@ -382,7 +382,7 @@ VOID WINAPI GetSystemInfo(
         cachedsi.dwPageSize                  = sbi.PageSize;
         cachedsi.lpMinimumApplicationAddress = sbi.LowestUserAddress;
         cachedsi.lpMaximumApplicationAddress = sbi.HighestUserAddress;
-        cachedsi.dwNumberOfProcessors        = sbi.ActiveProcessors;
+        cachedsi.dwNumberOfProcessors        = sbi.NumberOfProcessors;
         cachedsi.dwAllocationGranularity     = sbi.AllocationGranularity;
 
 	/* choose sensible defaults ...

dlls/ntdll/virtual.c

@@ -1380,7 +1380,7 @@ void virtual_get_system_info( SYSTEM_BASIC_INFORMATION *info )
     info->AllocationGranularity   = get_mask(0) + 1;
     info->LowestUserAddress       = (void *)0x10000;
     info->HighestUserAddress      = (char *)user_space_limit - 1;
-    info->ActiveProcessors        = NtCurrentTeb()->Peb->NumberOfProcessors;
+    info->ActiveProcessorsAffinityMask = (1 << NtCurrentTeb()->Peb->NumberOfProcessors) - 1;
     info->NumberOfProcessors      = NtCurrentTeb()->Peb->NumberOfProcessors;
 }
 

include/winternl.h

@@ -1196,7 +1196,7 @@ typedef struct _SYSTEM_BASIC_INFORMATION {
     ULONG_PTR AllocationGranularity;
     PVOID     LowestUserAddress;
     PVOID     HighestUserAddress;
-    ULONG_PTR ActiveProcessors;
+    ULONG_PTR ActiveProcessorsAffinityMask;
     BYTE      NumberOfProcessors;
 #else
     BYTE Reserved1[24];