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SubjectRe: [PATCH] efi/libstub: Indicate clang the relocation mode for arm64
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On 05/09/2017 12:36 PM, Matthias Kaehlcke wrote:
> From: Greg Hackmann <ghackmann@google.com>
>
> Without any extra guidance, clang will generate libstub with either
> absolute or relative ELF relocations. Use the right combination of
> -fpic and -fno-pic on different files to avoid this.
>
> Signed-off-by: Greg Hackmann <ghackmann@google.com>
> Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> drivers/firmware/efi/libstub/Makefile | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index f7425960f6a5..ccbaaf4d8650 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -11,6 +11,9 @@ cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -O2 \
> -mno-mmx -mno-sse
>
> cflags-$(CONFIG_ARM64) := $(subst -pg,,$(KBUILD_CFLAGS))
> +ifeq ($(cc-name),clang)
> +cflags-$(CONFIG_ARM64) += -fpic
> +endif
> cflags-$(CONFIG_ARM) := $(subst -pg,,$(KBUILD_CFLAGS)) \
> -fno-builtin -fpic -mno-single-pic-base
>
> @@ -38,6 +41,9 @@ $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
>
> lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o string.o random.o \
> $(patsubst %.c,lib-%.o,$(arm-deps))
> +ifeq ($(cc-name),clang)
> +CFLAGS_arm64-stub.o += -fno-pic
> +endif
>
> lib-$(CONFIG_ARM) += arm32-stub.o
> lib-$(CONFIG_ARM64) += arm64-stub.o
>

NAK.

This patch was labeled "HACK:" in our experimental tree. There's no
rhyme or reason to why this combination of -f[no-]pic flags generates
code without problematic relocations. It's inherently fragile, and was
only intended as a temporary workaround until I (or someone more
familiar with EFI) got a chance to revisit the problem.

Unless the gcc CFLAGS are also an artifact of "mess with -f[no-]pic
until the compiler generates what you want", this doesn't belong upstream.

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