[yakkety,RFC,v1] disable -pie when gcc has it enabled by default

From: Steve Beattie <steve.beattie@canonical.com>

In Ubuntu 16.10, gcc's defaults have been set to build Position
Independent Executables (PIE) on amd64 and ppc64le (gcc was configured
this way for s390x in Ubuntu 16.04 LTS). This breaks the kernel build on
amd64. The following patch disables pie for x86 builds (though not yet
verified to work with gcc configured to build PIE by default i386 --
we're not planning to enable it for that architecture).

The intent is for this patch to go upstream after expanding it to
additional architectures where needed, but I wanted to ensure that
we could build 16.10 kernels first. I've successfully built kernels
and booted them with this patch applied using the 16.10 compiler.

Patch is against yakkety.git, but also applies with minor movement
(no fuzz) against current linus.git.

Signed-off-by: Steve Beattie <steve.beattie@canonical.com>

On Thu, Apr 28, 2016 at 11:33:25PM -0700, Steve Beattie wrote:
> From: Steve Beattie <steve.beattie@canonical.com>
> 
> In Ubuntu 16.10, gcc's defaults have been set to build Position
> Independent Executables (PIE) on amd64 and ppc64le (gcc was configured
> this way for s390x in Ubuntu 16.04 LTS). This breaks the kernel build on
> amd64. The following patch disables pie for x86 builds (though not yet
> verified to work with gcc configured to build PIE by default i386 --
> we're not planning to enable it for that architecture).
> 
> The intent is for this patch to go upstream after expanding it to
> additional architectures where needed, but I wanted to ensure that
> we could build 16.10 kernels first. I've successfully built kernels
> and booted them with this patch applied using the 16.10 compiler.
> 
> Patch is against yakkety.git, but also applies with minor movement
> (no fuzz) against current linus.git.
> 
> Signed-off-by: Steve Beattie <steve.beattie@canonical.com>
> 
> diff --git a/Makefile b/Makefile
> index e27da43..e4e8331 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -640,6 +640,11 @@ 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)
> +
>  # Handle stack protector mode.
>  #
>  # Since kbuild can potentially perform two passes (first with the old
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 4086abc..84d1cc8 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -27,6 +27,7 @@ REALMODE_CFLAGS	:= $(M16_CFLAGS) -g -Os -D__KERNEL__ \
>  		   -mno-mmx -mno-sse \
>  		   $(call cc-option, -ffreestanding) \
>  		   $(call cc-option, -fno-stack-protector) \
> +		   $(call cc-option, -fno-pie) \
>  		   $(call cc-option, -mpreferred-stack-boundary=2)
>  export REALMODE_CFLAGS
>  
> @@ -129,7 +130,7 @@ endif
>  # Make sure compiler does not have buggy stack-protector support.
>  ifdef CONFIG_CC_STACKPROTECTOR
>  	cc_has_sp := $(srctree)/scripts/gcc-x86_$(BITS)-has-stack-protector.sh
> -        ifneq ($(shell $(CONFIG_SHELL) $(cc_has_sp) $(CC) $(KBUILD_CPPFLAGS) $(biarch)),y)
> +        ifneq ($(shell $(CONFIG_SHELL) $(cc_has_sp) $(CC) -fno-pie $(KBUILD_CPPFLAGS) $(biarch)),y)
>                  $(warning stack-protector enabled but compiler support broken)
>          endif
>  endif
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 265c0ed..9677975 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -44,6 +44,7 @@ export CPPFLAGS_vdso.lds += -P -C
>  VDSO_LDFLAGS_vdso.lds = -m64 -Wl,-soname=linux-vdso.so.1 \
>  			-Wl,--no-undefined \
>  			-Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096 \
> +			$(call ld-option, -no-pie) \
>  			$(DISABLE_LTO)
>  
>  $(obj)/vdso64.so.dbg: $(src)/vdso.lds $(vobjs) FORCE
> @@ -67,6 +68,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
>  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
>         $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
>         -fno-omit-frame-pointer -foptimize-sibling-calls \
> +       $(call cc-option, -fno-pie) \
>         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
>  
>  $(vobjs): KBUILD_CFLAGS += $(CFL)
> @@ -140,6 +142,7 @@ KBUILD_CFLAGS_32 := $(filter-out -mcmodel=kernel,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
> +KBUILD_CFLAGS_32 += $(call cc-option, -no-pie)
>  KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
>  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
>  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
> 
> 
> -- 
> Steve Beattie
> <sbeattie@ubuntu.com>
> http://NxNW.org/~steve/

Thanks steve.  Will sort this out.

-apw