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

[Andy Whitcroft]

On Thu, Apr 28, 2016 at 11:33:25PM -0700, Steve Beattie wrote:
> From: Steve Beattie <steve.beattie at 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 at 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 at ubuntu.com>
> http://NxNW.org/~steve/

Thanks steve.  Will sort this out.

-apw