Hi Nicolas, the flags are necessary (but one is misnamed). See platforms/Cross/vm/sqCogStackAlignment.h for use and default definition of STACK_ALIGN_BYTES. See src/plugins/SqueakFFIPrims/X64Win64FFIPlugin.c for use of ALLOCA_LIES_SO_SETSP_BEFORE_CALL. But ALLOCA_LIES_SO_SETSP_BEFORE_CALL is set up by X64Win64FFIPlugin.c so we don't need it on the command line.