Re: [PATCH] efi/libstub: Indicate clang the relocation mode for arm64
From: Greg Hackmann
Date: Tue May 09 2017 - 16:50:49 EST
On 05/09/2017 12:36 PM, Matthias Kaehlcke wrote:
From: Greg Hackmann <ghackmann@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Bernhard RosenkrÃnzer <Bernhard.Rosenkranzer@xxxxxxxxxx>
Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
---
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.