Makefile: move stack-protector compiler breakage test earlier

In order to make stack-protector failures warn instead of unconditionally
breaking the build, this moves the compiler output sanity-check earlier,
and sets a flag for later testing.  Future patches can choose to warn or
fail, depending on the flag value.

Link: http://lkml.kernel.org/r/1510076320-69931-2-git-send-email-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Makefile

@@ -696,6 +696,12 @@ endif
 ifdef CONFIG_CC_STACKPROTECTOR
   stackp-path := $(srctree)/scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh
   stackp-check := $(wildcard $(stackp-path))
+  # If the wildcard test matches a test script, run it to check functionality.
+  ifdef stackp-check
+    ifneq ($(shell $(CONFIG_SHELL) $(stackp-check) $(CC) $(KBUILD_CPPFLAGS) $(biarch)),y)
+      stackp-broken := y
+    endif
+  endif
 endif
 KBUILD_CFLAGS += $(stackp-flag)
 
@@ -1098,11 +1104,9 @@ ifdef stackp-name
   endif
 endif
 # Make sure compiler does not have buggy stack-protector support.
-ifdef stackp-check
-  ifneq ($(shell $(CONFIG_SHELL) $(stackp-check) $(CC) $(KBUILD_CPPFLAGS) $(biarch)),y)
+ifdef stackp-broken
 	@echo Cannot use CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
                   $(stackp-flag) available but compiler is broken >&2 && exit 1
-  endif
 endif
 	@: