Может это поможет:
ThreadContext
Points to a structure that specifies the initial values of the processor registers for the
thread.
UserStack
Points to a structure that specifies the user mode stack of the thread.

typedef struct _USER_STACK {
PVOID FixedStackBase;
PVOID FixedStackLimit;
PVOID ExpandableStackBase;
PVOID ExpandableStackLimit;
PVOID ExpandableStackBottom;
} USER_STACK, *PUSER_STACK;