[PATCH v3 2/2] kbuild: Add option to fail build on vmlinux objtool issues

[Brendan Jackman <jackmanb@google.com>]

NOINSTR_VALIDATION is pretty helpful for detecting bugs, it would be
helpful for the build to fail when those bugs arise.

If necessary it would be possible to enable this for individual
warnings, it seems unlikely there's a use-case for that though. So
for now just add a global setting.

When the this new option, OBJTOOL_WERROR, is set, also add --verbose:
if the build is failing then it's better to spit out any information
that might help diagnose the failure, even if that risks a very verbose
output.

Checkpatch-args: --ignore=CONFIG_DESCRIPTION
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 lib/Kconfig.debug    | 10 ++++++++++
 scripts/Makefile.lib |  1 +
 2 files changed, 11 insertions(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f3d72370587936fa373129cc9b246f15dac907be..3ee92da4733a3a504991d5dbb4d0cee84f519d64 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -545,6 +545,16 @@ config FRAME_POINTER
 config OBJTOOL
 	bool
 
+config OBJTOOL_WERROR
+	bool "Run objtool with warnings as errors"
+	default n
+	depends on OBJTOOL
+	help
+	  Fail the build when objtool produces warnings.
+
+	  By default, objtool just prints warnings to the terminal without
+	  causing a build failure. This config changes that.
+
 config STACK_VALIDATION
 	bool "Compile-time stack metadata validation"
 	depends on HAVE_STACK_VALIDATION && UNWINDER_FRAME_POINTER
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 7395200538da89a2f6e6d21f8959f3f60d291d79..a1b264e532920dd649122968d5782ca8eff34ad9 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -277,6 +277,7 @@ objtool-args-$(CONFIG_HAVE_STATIC_CALL_INLINE)		+= --static-call
 objtool-args-$(CONFIG_HAVE_UACCESS_VALIDATION)		+= --uaccess
 objtool-args-$(CONFIG_GCOV_KERNEL)			+= --no-unreachable
 objtool-args-$(CONFIG_PREFIX_SYMBOLS)			+= --prefix=$(CONFIG_FUNCTION_PADDING_BYTES)
+objtool-args-$(CONFIG_OBJTOOL_WERROR)			+= --Werror --verbose
 
 objtool-args = $(objtool-args-y)					\
 	$(if $(delay-objtool), --link)					\

-- 
2.47.1.613.gc27f4b7a9f-goog