XENVERSION can be set by a .extraversion file at root of Linux build tree.
# Added '-march' and '-mpreferred-stack-boundary' support
#
-XENVERSION ?= -xen
+XENVERSION ?= $(shell cat .extraversion 2>/dev/null || echo "-xen")
EXTRAVERSION := $(EXTRAVERSION)$(XENVERSION)
# If no .config file exists then use the appropriate defconfig-* file
# Copyright (C) 2004 by Christian Limpach
#
-XENVERSION ?= -xen
+XENVERSION ?= $(shell cat .extraversion 2>/dev/null || echo "-xen")
EXTRAVERSION := $(EXTRAVERSION)$(XENVERSION)
XENARCH := $(subst ",,$(CONFIG_XENARCH))