[PATCH v2 1/3] Makefile: Move stack-protector compiler breakage test earlier

[Kees Cook]

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.

Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: linux-kbuild@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index cf007a31d575..caa3f7e6f524 100644
--- a/Makefile
+++ b/Makefile
@@ -692,6 +692,12 @@ 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)
 
@@ -1087,11 +1093,9 @@ 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
 	@:
 
-- 
2.7.4