From: Joel Stanley joel@jms.id.au
[ Upstream commit 72e7bcc2cdf82bf03caaa5e6c9b0134c2fc2ee7d ]
When building for ppc32 with clang these flags are unsupported:
-ffixed-r2 and -mmultiple
llvm's lib/Target/PowerPC/PPCRegisterInfo.cpp marks r2 as reserved on when building for SVR4ABI and !ppc64:
// The SVR4 ABI reserves r2 and r13 if (Subtarget.isSVR4ABI()) { // We only reserve r2 if we need to use the TOC pointer. If we have no // explicit uses of the TOC pointer (meaning we're a leaf function with // no constant-pool loads, etc.) and we have no potential uses inside an // inline asm block, then we can treat r2 has an ordinary callee-saved // register. const PPCFunctionInfo *FuncInfo = MF.getInfo<PPCFunctionInfo>(); if (!TM.isPPC64() || FuncInfo->usesTOCBasePtr() || MF.hasInlineAsm()) markSuperRegs(Reserved, PPC::R2); // System-reserved register markSuperRegs(Reserved, PPC::R13); // Small Data Area pointer register }
This means we can safely omit -ffixed-r2 when building for 32-bit targets.
The -mmultiple/-mno-multiple flags are not supported by clang, so platforms that might support multiple miss out on using multiple word instructions.
We wrap these flags in cc-option so that when Clang gains support the kernel will be able use these flags.
Clang 8 can then build a ppc44x_defconfig which boots in Qemu:
make CC=clang-8 ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- ppc44x_defconfig ./scripts/config -e CONFIG_DEVTMPFS -d DEVTMPFS_MOUNT make CC=clang-8 ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu-
qemu-system-ppc -M bamboo \ -kernel arch/powerpc/boot/zImage \ -dtb arch/powerpc/boot/dts/bamboo.dtb \ -initrd ~/ppc32-440-rootfs.cpio \ -nographic -serial stdio -monitor pty -append "console=ttyS0"
Link: https://github.com/ClangBuiltLinux/linux/issues/261 Link: https://bugs.llvm.org/show_bug.cgi?id=39556 Link: https://bugs.llvm.org/show_bug.cgi?id=39555 Signed-off-by: Joel Stanley joel@jms.id.au Reviewed-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/Makefile | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile index c4c03992ee828..dfcb698ec8f3b 100644 --- a/arch/powerpc/Makefile +++ b/arch/powerpc/Makefile @@ -145,7 +145,14 @@ endif CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcmodel=medium,$(call cc-option,-mminimal-toc)) CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mno-pointers-to-nested-functions)
-CFLAGS-$(CONFIG_PPC32) := -ffixed-r2 $(MULTIPLEWORD) +# Clang unconditionally reserves r2 on ppc32 and does not support the flag +# https://bugs.llvm.org/show_bug.cgi?id=39555 +CFLAGS-$(CONFIG_PPC32) := $(call cc-option, -ffixed-r2) + +# Clang doesn't support -mmultiple / -mno-multiple +# https://bugs.llvm.org/show_bug.cgi?id=39556 +CFLAGS-$(CONFIG_PPC32) += $(call cc-option, $(MULTIPLEWORD)) + CFLAGS-$(CONFIG_PPC32) += $(call cc-option,-mno-readonly-in-sdata)
ifdef CONFIG_PPC_BOOK3S_64