[Xen-devel] [PATCH for-4.7] xen/build: Fix build with Clang

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s 607044bf9 "build: avoid putting local absolute symbols in symbol tables"
breaks the build with Clang, as the command line argument isn't understood.

Clang does not appear to have any equivielent option, and already has
outstanding issues with duplicate symbols.  Excluding this option makes the
problem no worse.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>

The clang build already has many duplicate symbols for some reason I have yet
to identify, e.g.

  Duplicate symbol 'asid.c#get_cpu_info' (ffff82d0801e6840 != ffff82d0801c8190)
  Duplicate symbol 'ats.c#__list_add' (ffff82d08015b900 != ffff82d0801546a0)
  Duplicate symbol 'common.c#clear_bit' (ffff82d080213560 != ffff82d0801baf10)
  Duplicate symbol 'common.c#constant_test_bit' (ffff82d080213550 != 
ffff82d0801ba750)
  Duplicate symbol 'common.c#cpumask_check' (ffff82d080218c50 != 
ffff82d0801baf20)
  Duplicate symbol 'common.c#cpumask_clear_cpu' (ffff82d080214990 != 
ffff82d0801bae40)
  Duplicate symbol 'common.c#get_cpu_info' (ffff82d080212210 != 
ffff82d0801bad20)

The resulting binary does function.  Someone with more time can investigate
making symbol handling work better with Clang
---
 xen/Rules.mk | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index d4dffde..7183d69 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -50,9 +50,15 @@ ALL_OBJS-$(CONFIG_X86)   += $(BASEDIR)/crypto/built_in.o
 CFLAGS += -nostdinc -fno-builtin -fno-common
 CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
 CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
-CFLAGS += -Wa,--strip-local-absolute
 CFLAGS += '-D__OBJECT_FILE__="$@"'
 
+ifneq ($(clang),y)
+# Clang doesn't understand this command line argument, and doesn't appear to
+# have an suitable alternative.  The resulting compiled binary does function,
+# but has an excessively large symbol table.
+CFLAGS += -Wa,--strip-local-absolute
+endif
+
 CFLAGS-$(verbose)       += -DVERBOSE
 CFLAGS-$(crash_debug)   += -DCRASH_DEBUG
 CFLAGS-$(perfc)         += -DPERF_COUNTERS
-- 
2.1.4


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