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[Xen-devel] [PATCH] x86/build: Fix -mskip-rax-setup handling

The way -mskip-rax-setup is currently specified results in compiler support
being evaluated per translation unit, rather than per subdir.  Switch to using
cc-add-option instead.

This drops the number of callouts from 428 to 60.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Anthony PERARD <anthony.perard@xxxxxxxxxx>

This drops about 0.5s from my ccache-accelerated but otherwise-clean build,
and will likely have a more pronounced difference on older hardware.  If it
wants backporting, it wants to go back in this form.

Alternatively, it would be nice to get this moved to Kconfig time.  Anthony:
Do you have any part of your series already doing this, or any suggestions on
how best to do it without colliding with your work?
 xen/arch/x86/Rules.mk | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk
index e69b8e697c..78fa312d38 100644
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -63,7 +63,8 @@ CFLAGS += -mno-red-zone -fpic -fno-asynchronous-unwind-tables
 # Xen doesn't use SSE interally.  If the compiler supports it, also skip the
 # SSE setup for variadic function calls.
-CFLAGS += -mno-sse $(call cc-option,$(CC),-mskip-rax-setup)
+CFLAGS += -mno-sse
+$(call cc-option-add,CFLAGS,CC,-mskip-rax-setup)
 # Compile with thunk-extern, indirect-branch-register if avaiable.

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