[PATCH] xen: Work around Clang -E vs -Wunicode bug

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

https://github.com/llvm/llvm-project/issues/60958

While trying to work around a different Clang-IAS bug, I stubled onto

  In file included from arch/x86/asm-macros.c:3:
  ./arch/x86/include/asm/spec_ctrl_asm.h:144:19: error: \u used with
  no following hex digits; treating as '\' followed by identifier 
[-Werror,-Wunicode]
  .L\@_fill_rsb_loop\uniq:
                    ^

It turns out that Clang -E is sensitive to the file extension of the source
file it is processing.

asm-macros should really have been .S from the outset, as it is ultimately
generating assembly, not C.  Rename it, which causes Clang not to complain.

We need to introduce rules for generating a .i file from .S, and substituting
c_flags for a_flags lets us drop the now-redundant -D__ASSEMBLY__.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 xen/Rules.mk                                | 6 ++++++
 xen/arch/x86/Makefile                       | 2 +-
 xen/arch/x86/{asm-macros.c => asm-macros.S} | 0
 3 files changed, 7 insertions(+), 1 deletion(-)
 rename xen/arch/x86/{asm-macros.c => asm-macros.S} (100%)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index d6b7cec0a882..59072ae8dff2 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -273,6 +273,9 @@ $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): 
$(obj)/%.init.o: $(obj)/%.o
 quiet_cmd_cpp_i_c = CPP     $@
 cmd_cpp_i_c = $(CPP) $(call cpp_flags,$(c_flags)) -MQ $@ -o $@ $<
 
+quiet_cmd_cpp_i_S = CPP     $@
+cmd_cpp_i_S = $(CPP) $(call cpp_flags,$(a_flags)) -MQ $@ -o $@ $<
+
 quiet_cmd_cc_s_c = CC      $@
 cmd_cc_s_c = $(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -S $< -o $@
 
@@ -282,6 +285,9 @@ cmd_cpp_s_S = $(CPP) $(call cpp_flags,$(a_flags)) -MQ $@ -o 
$@ $<
 $(obj)/%.i: $(src)/%.c FORCE
        $(call if_changed_dep,cpp_i_c)
 
+$(obj)/%.i: $(src)/%.S FORCE
+       $(call if_changed_dep,cpp_i_S)
+
 $(obj)/%.s: $(src)/%.c FORCE
        $(call if_changed_dep,cc_s_c)
 
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 177a2ff74272..5accbe4c6746 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -240,7 +240,7 @@ $(obj)/efi/buildid.o $(obj)/efi/relocs-dummy.o: ;
 .PHONY: include
 include: $(objtree)/arch/x86/include/asm/asm-macros.h
 
-$(obj)/asm-macros.i: CFLAGS-y += -D__ASSEMBLY__ -P
+$(obj)/asm-macros.i: CFLAGS-y += -P
 
 $(objtree)/arch/x86/include/asm/asm-macros.h: $(obj)/asm-macros.i 
$(src)/Makefile
        $(call filechk,asm-macros.h)
diff --git a/xen/arch/x86/asm-macros.c b/xen/arch/x86/asm-macros.S
similarity index 100%
rename from xen/arch/x86/asm-macros.c
rename to xen/arch/x86/asm-macros.S
-- 
2.30.2