linux-kernel - Re: [PATCH 2/2] kbuild: remove cc-option test of -ffreestanding

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Date:   Fri, 26 Jun 2020 12:58:24 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] kbuild: remove cc-option test of -ffreestanding

On Fri, Jun 26, 2020 at 11:59 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Some Makefiles already pass -ffreestanding unconditionally.
> For example, arch/arm64/lib/Makefile, arch/x86/purgatory/Makefile.
> No problem report so far about hard-coding this option. So, we can
> assume all supported compilers know -ffreestanding.
>
> I confirmed GCC 4.8 and Clang manuals document this option.
>
> Get rid of cc-option from -ffreestanding.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>
>  arch/s390/Makefile                    | 2 +-
>  arch/x86/Makefile                     | 2 +-
>  arch/x86/boot/compressed/Makefile     | 2 +-
>  drivers/firmware/efi/libstub/Makefile | 2 +-
>  4 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/Makefile b/arch/s390/Makefile
> index 8dfa2cf1f05c..ba94b03c8b2f 100644
> --- a/arch/s390/Makefile
> +++ b/arch/s390/Makefile
> @@ -27,7 +27,7 @@ KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2
>  KBUILD_CFLAGS_DECOMPRESSOR += -DDISABLE_BRANCH_PROFILING -D__NO_FORTIFY
>  KBUILD_CFLAGS_DECOMPRESSOR += -fno-delete-null-pointer-checks -msoft-float
>  KBUILD_CFLAGS_DECOMPRESSOR += -fno-asynchronous-unwind-tables
> -KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-option,-ffreestanding)
> +KBUILD_CFLAGS_DECOMPRESSOR += -ffreestanding
>  KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, address-of-packed-member)
>  KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),-g)
>  KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO_DWARF4), $(call cc-option, -gdwarf-4,))
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 89c3cdfba753..edc68538a04e 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -36,7 +36,7 @@ REALMODE_CFLAGS       := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
>                    -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
>                    -mno-mmx -mno-sse
>
> -REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
> +REALMODE_CFLAGS += -ffreestanding

See also
commit 032a2c4f65a2 ("x86/build: Use __cc-option for boot code
compiler options")
for additional context (to fellow reviewers).

>  REALMODE_CFLAGS += -fno-stack-protector
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index c88a31569a5e..b7beabecef8a 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -35,7 +35,7 @@ cflags-$(CONFIG_X86_32) := -march=i386
>  cflags-$(CONFIG_X86_64) := -mcmodel=small
>  KBUILD_CFLAGS += $(cflags-y)
>  KBUILD_CFLAGS += -mno-mmx -mno-sse
> -KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> +KBUILD_CFLAGS += -ffreestanding
>  KBUILD_CFLAGS += -fno-stack-protector
>  KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
>  KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index f8418763cd79..296b18fbd7a2 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -28,7 +28,7 @@ cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
>  KBUILD_CFLAGS                  := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
>                                    -include $(srctree)/drivers/firmware/efi/libstub/hidden.h \
>                                    -D__NO_FORTIFY \
> -                                  $(call cc-option,-ffreestanding) \
> +                                  -ffreestanding \
>                                    -fno-stack-protector \
>                                    $(call cc-option,-fno-addrsig) \
>                                    -D__DISABLE_EXPORTS
> --

-- 
Thanks,
~Nick Desaulniers