Re: [RFC PATCH] kbuild: add -fno-PIE

[Shuah Khan]

On Fri, Oct 21, 2016 at 5:16 AM, Sebastian Andrzej Siewior
<bigeasy@xxxxxxxxxxxxx> wrote:
> Debian started to build the gcc with --enable-default-pie by default so the
> kernel build ends before it starts properly with:
> |kernel/bounds.c:1:0: error: code model kernel does not support PIC mode
>
> Is this okay or do we want some kind of check to see if -fno-PIE is supported?
> It is mentioned in the 4.4.7 gcc manpage is it is not *that* new :)
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
>  Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index bf6e44a421df..97296d66b586 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -398,7 +398,7 @@ KBUILD_CPPFLAGS := -D__KERNEL__
>  KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
>                    -fno-strict-aliasing -fno-common \
>                    -Werror-implicit-function-declaration \
> -                  -Wno-format-security \
> +                  -Wno-format-security -fno-PIE \
>                    -std=gnu89
>
>  KBUILD_AFLAGS_KERNEL :=
> --
> 2.9.3
>

Hi,

I ran into this when I upgraded to Ubuntu 16.10. Ubuntu kernel team
has a patch posted for Ubuntu kernels. The patch talks about needing
have this work for other architectures. I applied part of the change
from the original Ubuntu patch -
https://patchwork.ozlabs.org/patch/616621/

Anyway, the following worked for me on x86-64 - both 4.8.4 and 4.9


diff --git a/Makefile b/Makefile
index 82a36ab..0a01ad1 100644
--- a/Makefile
+++ b/Makefile
@@ -651,6 +651,11 @@ ifneq ($(CONFIG_FRAME_WARN),0)
 KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
 endif

+# force no-pie for distro compilers that enable pie by default
+KBUILD_CFLAGS += $(call cc-option, -fno-pie)
+KBUILD_CFLAGS += $(call cc-option, -no-pie)
+KBUILD_AFLAGS += $(call cc-option, -fno-pie)
+
 # This selects the stack protector compiler flag. Testing it is delayed
 # until after .config has been reprocessed, in the prepare-compiler-check
 # target.

thanks,
-- Shuah