ARM: 8500/1: fix atags_to_fdt with stack-protector-strong

Building with CONFIG_CC_STACKPROTECTOR_STRONG triggers protection code
generation under CONFIG_ARM_ATAG_DTB_COMPAT but this is too early for
being able to use any of the stack_chk code. Explicitly disable it for
only the atags_to_fdt bits.
Suggested-by: Nzhxihu <zhxihu@marvell.com>
Signed-off-by: NKees Cook <keescook@chromium.org>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/boot/compressed/Makefile

@@ -106,6 +106,15 @@ ORIG_CFLAGS := $(KBUILD_CFLAGS)
 KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS))
 endif
 
+# -fstack-protector-strong triggers protection checks in this code,
+# but it is being used too early to link to meaningful stack_chk logic.
+nossp_flags := $(call cc-option, -fno-stack-protector)
+CFLAGS_atags_to_fdt.o := $(nossp_flags)
+CFLAGS_fdt.o := $(nossp_flags)
+CFLAGS_fdt_ro.o := $(nossp_flags)
+CFLAGS_fdt_rw.o := $(nossp_flags)
+CFLAGS_fdt_wip.o := $(nossp_flags)
+
 ccflags-y := -fpic -mno-single-pic-base -fno-builtin -I$(obj)
 asflags-y := -DZIMAGE