[XEN PATCH v9 08/30] build: fix enforce unique symbols for recent clang version

[Anthony PERARD <anthony.perard@citrix.com>]

clang 6.0 and newer behave like gcc in regards for the FILE symbol, so
only the filename rather than the full path to the source file.

clang 3.8.1-24 (in our debian:stretch container) and 3.5.0-10
(in our debian:jessie container) do store the full path to the source
file in the FILE symbol.

Also, based on commit 81ecb38b83 ("build: provide option to
disambiguate symbol names"), which were using clang 5, the change of
behavior likely happened in clang 6.0.

This means that we also need to check clang version to figure out
which command we need to use to redefine symbol.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---

"enforce unique symbols" works by chance with recent clang version.
The few object built from source in subdir don't pose an issue.
---

Notes:
    v9:
    - checking for clang 6 instead of clang 4, based on 81ecb38b83, and
      update commit message.
    
    v8:
    - new patch, extracted from "build: build everything from the root dir, use obj=$subdir"

 xen/Rules.mk               | 2 +-
 xen/scripts/Kbuild.include | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index 60d1d6c4f583..1e7f47a3d8a8 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -166,7 +166,7 @@ SRCPATH := $(patsubst $(BASEDIR)/%,%,$(CURDIR))
 quiet_cmd_cc_o_c = CC      $@
 ifeq ($(CONFIG_ENFORCE_UNIQUE_SYMBOLS),y)
     cmd_cc_o_c = $(CC) $(c_flags) -c $< -o $(dot-target).tmp -MQ $@
-    ifeq ($(CONFIG_CC_IS_CLANG),y)
+    ifeq ($(CONFIG_CC_IS_CLANG)$(call clang-ifversion,-lt,600,y),yy)
         cmd_objcopy_fix_sym = $(OBJCOPY) --redefine-sym $<=$(SRCPATH)/$< $(dot-target).tmp $@
     else
         cmd_objcopy_fix_sym = $(OBJCOPY) --redefine-sym $(<F)=$(SRCPATH)/$< $(dot-target).tmp $@
diff --git a/xen/scripts/Kbuild.include b/xen/scripts/Kbuild.include
index 73caf238d42c..4875bb28c282 100644
--- a/xen/scripts/Kbuild.include
+++ b/xen/scripts/Kbuild.include
@@ -59,6 +59,8 @@ ld-option = $(call success,$(LD) -v $(1))
 # Usage:  EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
 cc-ifversion = $(shell [ $(CONFIG_GCC_VERSION)0 $(1) $(2)000 ] && echo $(3) || echo $(4))
 
+clang-ifversion = $(shell [ $(CONFIG_CLANG_VERSION)0 $(1) $(2)000 ] && echo $(3) || echo $(4))
+
 # Shorthand for $(MAKE) clean
 # Usage:
 # $(MAKE) $(clean) dir
-- 
Anthony PERARD