[PATCH-for-4.14 v2 1/2] xen: fix build with CONFIG_HYPFS_CONFIG enabled

[Juergen Gross <jgross@xxxxxxxx>]

Commit 58263ed7713e ("xen: add /buildinfo/config entry to hypervisor
filesystem") added a dependency to .config, but the hypervisor's build
config could be have another name via setting KCONFIG_CONFIG.

Fix that by using $(KCONFIG_CONFIG) instead. Additionally reference
the config file via $(XEN_ROOT) instead of a relative path.

Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2:
- accept an absolute path in KCONFIG_CONFIG (Jan Beulich)
---
 xen/common/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/common/Makefile b/xen/common/Makefile
index 91581e1815..fc2c8eb4a3 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -75,7 +75,8 @@ obj-$(CONFIG_UBSAN) += ubsan/
 obj-$(CONFIG_NEEDS_LIBELF) += libelf/
 obj-$(CONFIG_HAS_DEVICE_TREE) += libfdt/
 
-config.gz: ../.config
+CONF_FILE := $(if $(patsubst 
/%,,$(KCONFIG_CONFIG)),$(XEN_ROOT)/xen/$(KCONFIG_CONFIG),$(KCONFIG_CONFIG))
+config.gz: $(CONF_FILE)
        gzip -c $< >$@
 
 config_data.o: config.gz
-- 
2.26.2