* [PATCH v2] kbuild: add -fcf-protection=none when using retpoline flags
@ 2019-07-17 16:06 Seth Forshee
2019-07-17 17:22 ` Masahiro Yamada
0 siblings, 1 reply; 2+ messages in thread
From: Seth Forshee @ 2019-07-17 16:06 UTC (permalink / raw)
To: Masahiro Yamada, Michal Marek; +Cc: Josh Poimboeuf, linux-kbuild, linux-kernel
The gcc -fcf-protection=branch option is not compatible with
-mindirect-branch=thunk-extern. The latter is used when
CONFIG_RETPOLINE is selected, and this will fail to build with
a gcc which has -fcf-protection=branch enabled by default. Adding
-fcf-protection=none when building with retpoline enabled
prevents such build failures.
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
Makefile | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/Makefile b/Makefile
index 3e4868a6498b..73a94d1db2b6 100644
--- a/Makefile
+++ b/Makefile
@@ -878,6 +878,12 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
# change __FILE__ to the relative path from the srctree
KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
+# ensure -fcf-protection is disabled when using retpoline as it is
+# incompatible with -mindirect-branch=thunk-extern
+ifdef CONFIG_RETPOLINE
+KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none,)
+endif
+
# use the deterministic mode of AR if available
KBUILD_ARFLAGS := $(call ar-option,D)
--
2.20.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] kbuild: add -fcf-protection=none when using retpoline flags
2019-07-17 16:06 [PATCH v2] kbuild: add -fcf-protection=none when using retpoline flags Seth Forshee
@ 2019-07-17 17:22 ` Masahiro Yamada
0 siblings, 0 replies; 2+ messages in thread
From: Masahiro Yamada @ 2019-07-17 17:22 UTC (permalink / raw)
To: Seth Forshee
Cc: Michal Marek, Josh Poimboeuf, Linux Kbuild mailing list,
Linux Kernel Mailing List
On Thu, Jul 18, 2019 at 1:07 AM Seth Forshee <seth.forshee@canonical.com> wrote:
>
> The gcc -fcf-protection=branch option is not compatible with
> -mindirect-branch=thunk-extern. The latter is used when
> CONFIG_RETPOLINE is selected, and this will fail to build with
> a gcc which has -fcf-protection=branch enabled by default. Adding
> -fcf-protection=none when building with retpoline enabled
> prevents such build failures.
>
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Applied to linux-kbuild. Thanks.
--
Best Regards
Masahiro Yamada
^ permalink raw reply [flat|nested] 2+ messages in thread
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