[PATCH 4.9 23/59] x86/build: Use __cc-option for boot code compiler options

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthias Kaehlcke <mka@xxxxxxxxxxxx>

commit 032a2c4f65a2f81c93e161a11197ba19bc14a909 upstream.

cc-option is used to enable compiler options for the boot code if they
are available. The macro uses KBUILD_CFLAGS and KBUILD_CPPFLAGS for the
check, however these flags aren't used to build the boot code, in
consequence cc-option can yield wrong results. For example
-mpreferred-stack-boundary=2 is never set with a 64-bit compiler,
since the setting is only valid for 16 and 32-bit binaries. This
is also the case for 32-bit kernel builds, because the option -m32 is
added to KBUILD_CFLAGS after the assignment of REALMODE_CFLAGS.

Use __cc-option instead of cc-option for the boot mode options.
The macro receives the compiler options as parameter instead of using
KBUILD_C*FLAGS, for the boot code we pass REALMODE_CFLAGS.

Also use separate statements for the __cc-option checks instead
of performing them in the initial assignment of REALMODE_CFLAGS since
the variable is an input of the macro.

Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/Makefile |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -24,10 +24,11 @@ REALMODE_CFLAGS	:= $(M16_CFLAGS) -g -Os
 		   -DDISABLE_BRANCH_PROFILING \
 		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
 		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
-		   -mno-mmx -mno-sse \
-		   $(call cc-option, -ffreestanding) \
-		   $(call cc-option, -fno-stack-protector) \
-		   $(call cc-option, -mpreferred-stack-boundary=2)
+		   -mno-mmx -mno-sse
+
+REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
+REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
+REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -mpreferred-stack-boundary=2)
 export REALMODE_CFLAGS
 
 # BITS is used as extension for files which are available in a 32 bit