kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 424 insertions, 0 deletions

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
new file mode 100644
index 000000000..a58b10295
--- /dev/null
+++ b/arch/powerpc/Makefile
@@ -0,0 +1,424 @@
+# This file is included by the global makefile so that you can add your own
+# architecture-specific flags and dependencies.
+#
+# This file is subject to the terms and conditions of the GNU General Public
+# License.  See the file "COPYING" in the main directory of this archive
+# for more details.
+#
+# Copyright (C) 1994 by Linus Torvalds
+# Changes for PPC by Gary Thomas
+# Rewritten by Cort Dougan and Paul Mackerras
+#
+
+ifdef cross_compiling
+  ifeq ($(CROSS_COMPILE),)
+    # Auto detect cross compiler prefix.
+    # Look for: (powerpc(64(le)?)?)(-unknown)?-linux(-gnu)?-
+    CC_ARCHES := powerpc powerpc64 powerpc64le
+    CC_SUFFIXES := linux linux-gnu unknown-linux-gnu
+    CROSS_COMPILE := $(call cc-cross-prefix, $(foreach a,$(CC_ARCHES), \
+                       $(foreach s,$(CC_SUFFIXES),$(a)-$(s)-)))
+  endif
+endif
+
+HAS_BIARCH	:= $(call cc-option-yn, -m32)
+
+# Set default 32 bits cross compilers for vdso and boot wrapper
+CROSS32_COMPILE ?=
+
+# If we're on a ppc/ppc64/ppc64le machine use that defconfig, otherwise just use
+# ppc64le_defconfig because we have nothing better to go on.
+uname := $(shell uname -m)
+KBUILD_DEFCONFIG := $(if $(filter ppc%,$(uname)),$(uname),ppc64le)_defconfig
+
+new_nm := $(shell if $(NM) --help 2>&1 | grep -- '--synthetic' > /dev/null; then echo y; else echo n; fi)
+
+ifeq ($(new_nm),y)
+NM		:= $(NM) --synthetic
+endif
+
+# BITS is used as extension for files which are available in a 32 bit
+# and a 64 bit version to simplify shared Makefiles.
+# e.g.: obj-y += foo_$(BITS).o
+export BITS
+
+ifdef CONFIG_PPC64
+        BITS := 64
+else
+        BITS := 32
+endif
+
+machine-y = ppc
+machine-$(CONFIG_PPC64) += 64
+machine-$(CONFIG_CPU_LITTLE_ENDIAN) += le
+UTS_MACHINE := $(subst $(space),,$(machine-y))
+
+ifeq ($(CONFIG_PPC64)$(CONFIG_LD_IS_BFD),yy)
+# Have the linker provide sfpr if possible.
+# There is a corresponding test in arch/powerpc/lib/Makefile
+KBUILD_LDFLAGS_MODULE += --save-restore-funcs
+else
+KBUILD_LDFLAGS_MODULE += $(objtree)/arch/powerpc/lib/crtsavres.o
+endif
+
+ifdef CONFIG_CPU_LITTLE_ENDIAN
+KBUILD_CPPFLAGS	+= -mlittle-endian
+KBUILD_LDFLAGS	+= -EL
+LDEMULATION	:= lppc
+GNUTARGET	:= powerpcle
+MULTIPLEWORD	:= -mno-multiple
+KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-save-toc-indirect)
+else
+KBUILD_CPPFLAGS	+= $(call cc-option,-mbig-endian)
+KBUILD_LDFLAGS	+= -EB
+LDEMULATION	:= ppc
+GNUTARGET	:= powerpc
+MULTIPLEWORD	:= -mmultiple
+endif
+
+ifdef CONFIG_PPC64
+ifndef CONFIG_CC_IS_CLANG
+cflags-$(CONFIG_PPC64_ELF_ABI_V1)	+= $(call cc-option,-mabi=elfv1)
+cflags-$(CONFIG_PPC64_ELF_ABI_V1)	+= $(call cc-option,-mcall-aixdesc)
+aflags-$(CONFIG_PPC64_ELF_ABI_V1)	+= $(call cc-option,-mabi=elfv1)
+aflags-$(CONFIG_PPC64_ELF_ABI_V2)	+= -mabi=elfv2
+endif
+endif
+
+ifndef CONFIG_CC_IS_CLANG
+  cflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= -mno-strict-align
+endif
+
+cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(call cc-option,-mbig-endian)
+cflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= -mlittle-endian
+aflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(call cc-option,-mbig-endian)
+aflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= -mlittle-endian
+
+ifeq ($(HAS_BIARCH),y)
+KBUILD_CPPFLAGS	+= -m$(BITS)
+KBUILD_AFLAGS	+= -m$(BITS)
+KBUILD_LDFLAGS	+= -m elf$(BITS)$(LDEMULATION)
+endif
+
+LDFLAGS_vmlinux-y := -Bstatic
+LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie --no-dynamic-linker
+LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) += -z notext
+LDFLAGS_vmlinux	:= $(LDFLAGS_vmlinux-y)
+
+ifdef CONFIG_PPC64
+ifndef CONFIG_PPC_KERNEL_PCREL
+	# -mcmodel=medium breaks modules because it uses 32bit offsets from
+	# the TOC pointer to create pointers where possible. Pointers into the
+	# percpu data area are created by this method.
+	#
+	# The kernel module loader relocates the percpu data section from the
+	# original location (starting with 0xd...) to somewhere in the base
+	# kernel percpu data space (starting with 0xc...). We need a full
+	# 64bit relocation for this to work, hence -mcmodel=large.
+	KBUILD_CFLAGS_MODULE += -mcmodel=large
+endif
+endif
+
+CFLAGS-$(CONFIG_PPC64)	:= $(call cc-option,-mtraceback=no)
+ifdef CONFIG_PPC64_ELF_ABI_V2
+CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv2,$(call cc-option,-mcall-aixdesc))
+else
+ifndef CONFIG_CC_IS_CLANG
+CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv1)
+CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mcall-aixdesc)
+endif
+endif
+CFLAGS-$(CONFIG_PPC64)	+= -mcmodel=medium
+CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mno-pointers-to-nested-functions)
+CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mlong-double-128)
+
+# Clang unconditionally reserves r2 on ppc32 and does not support the flag
+# https://llvm.org/pr39555
+CFLAGS-$(CONFIG_PPC32)	:= $(call cc-option, -ffixed-r2)
+
+# Clang doesn't support -mmultiple / -mno-multiple
+# https://llvm.org/pr39556
+CFLAGS-$(CONFIG_PPC32)	+= $(call cc-option, $(MULTIPLEWORD))
+
+CFLAGS-$(CONFIG_PPC32)	+= $(call cc-option,-mno-readonly-in-sdata)
+
+CC_FLAGS_FPU		:= $(call cc-option,-mhard-float)
+CC_FLAGS_NO_FPU		:= $(call cc-option,-msoft-float)
+
+ifdef CONFIG_FUNCTION_TRACER
+ifdef CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY
+KBUILD_CPPFLAGS	+= -DCC_USING_PATCHABLE_FUNCTION_ENTRY
+ifdef CONFIG_PPC_FTRACE_OUT_OF_LINE
+CC_FLAGS_FTRACE := -fpatchable-function-entry=1
+else
+ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS # PPC32 only
+CC_FLAGS_FTRACE := -fpatchable-function-entry=3,1
+else
+CC_FLAGS_FTRACE := -fpatchable-function-entry=2
+endif
+endif
+else
+CC_FLAGS_FTRACE := -pg
+ifdef CONFIG_MPROFILE_KERNEL
+CC_FLAGS_FTRACE += -mprofile-kernel
+endif
+endif
+endif
+
+CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
+AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
+
+CFLAGS-y += $(CONFIG_TUNE_CPU)
+
+asinstr := $(call as-instr,lis 9$(comma)foo@high,-DHAVE_AS_ATHIGH=1)
+
+KBUILD_CPPFLAGS	+= -I $(srctree)/arch/powerpc $(asinstr)
+KBUILD_AFLAGS	+= $(AFLAGS-y)
+KBUILD_CFLAGS	+= $(CC_FLAGS_NO_FPU)
+KBUILD_CFLAGS	+= $(CFLAGS-y)
+
+CHECKFLAGS	+= -m$(BITS) -D__powerpc__ -D__powerpc$(BITS)__
+ifdef CONFIG_CPU_BIG_ENDIAN
+CHECKFLAGS	+= -D__BIG_ENDIAN__
+else
+CHECKFLAGS	+= -D__LITTLE_ENDIAN__
+endif
+
+ifdef CONFIG_476FPE_ERR46
+	KBUILD_LDFLAGS_MODULE += --ppc476-workaround \
+		-T $(srctree)/arch/powerpc/platforms/44x/ppc476_modules.lds
+endif
+
+# No prefix or pcrel
+ifdef CONFIG_PPC_KERNEL_PREFIXED
+KBUILD_CFLAGS += $(call cc-option,-mprefixed)
+else
+KBUILD_CFLAGS += $(call cc-option,-mno-prefixed)
+endif
+ifdef CONFIG_PPC_KERNEL_PCREL
+KBUILD_CFLAGS += $(call cc-option,-mpcrel)
+else
+KBUILD_CFLAGS += $(call cc-option,-mno-pcrel)
+endif
+
+# No AltiVec or VSX or MMA instructions when building kernel
+KBUILD_CFLAGS += $(call cc-option,-mno-altivec)
+KBUILD_CFLAGS += $(call cc-option,-mno-vsx)
+KBUILD_CFLAGS += $(call cc-option,-mno-mma)
+
+# No SPE instruction when building kernel
+# (We use all available options to help semi-broken compilers)
+KBUILD_CFLAGS += $(call cc-option,-mno-spe)
+KBUILD_CFLAGS += $(call cc-option,-mspe=no)
+
+# Don't emit .eh_frame since we have no use for it
+KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
+
+# Never use string load/store instructions as they are
+# often slow when they are implemented at all
+KBUILD_CFLAGS		+= $(call cc-option,-mno-string)
+
+KBUILD_AFLAGS += $(aflags-y)
+KBUILD_CFLAGS += $(cflags-y)
+
+# Default to zImage, override when needed
+all: zImage
+
+# With make 3.82 we cannot mix normal and wildcard targets
+BOOT_TARGETS1 := zImage zImage.initrd uImage
+BOOT_TARGETS2 := zImage% dtbImage% treeImage.% cuImage.% simpleImage.% uImage.%
+
+PHONY += $(BOOT_TARGETS1) $(BOOT_TARGETS2)
+
+boot := arch/powerpc/boot
+
+$(BOOT_TARGETS1): vmlinux
+	$(Q)$(MAKE) $(build)=$(boot) $(patsubst %,$(boot)/%,$@)
+$(BOOT_TARGETS2): vmlinux
+	$(Q)$(MAKE) $(build)=$(boot) $(patsubst %,$(boot)/%,$@)
+
+
+PHONY += bootwrapper_install
+bootwrapper_install:
+	$(Q)$(MAKE) $(build)=$(boot) $(patsubst %,$(boot)/%,$@)
+
+include $(srctree)/scripts/Makefile.defconf
+
+generated_configs += ppc64le_defconfig
+ppc64le_defconfig:
+	$(call merge_into_defconfig,ppc64_defconfig,le)
+
+generated_configs += ppc64le_guest_defconfig
+ppc64le_guest_defconfig:
+	$(call merge_into_defconfig,ppc64_defconfig,le guest kvm_guest)
+
+generated_configs += ppc64_guest_defconfig
+ppc64_guest_defconfig:
+	$(call merge_into_defconfig,ppc64_defconfig,be guest kvm_guest)
+
+generated_configs += pseries_le_defconfig
+pseries_le_defconfig: ppc64le_guest_defconfig
+
+generated_configs += pseries_defconfig
+pseries_defconfig: ppc64le_guest_defconfig
+
+generated_configs += powernv_be_defconfig
+powernv_be_defconfig:
+	$(call merge_into_defconfig,powernv_defconfig,be)
+
+generated_configs += mpc85xx_defconfig
+mpc85xx_defconfig:
+	$(call merge_into_defconfig,mpc85xx_base.config,\
+		85xx-32bit 85xx-hw fsl-emb-nonhw)
+
+generated_configs += mpc85xx_smp_defconfig
+mpc85xx_smp_defconfig:
+	$(call merge_into_defconfig,mpc85xx_base.config,\
+		85xx-32bit 85xx-smp 85xx-hw fsl-emb-nonhw)
+
+generated_configs += corenet32_smp_defconfig
+corenet32_smp_defconfig:
+	$(call merge_into_defconfig,corenet_base.config,\
+		85xx-32bit 85xx-smp 85xx-hw fsl-emb-nonhw dpaa)
+
+generated_configs += corenet64_smp_defconfig
+corenet64_smp_defconfig:
+	$(call merge_into_defconfig,corenet_base.config,\
+		85xx-64bit 85xx-smp altivec 85xx-hw fsl-emb-nonhw dpaa)
+
+generated_configs += mpc86xx_defconfig
+mpc86xx_defconfig:
+	$(call merge_into_defconfig,mpc86xx_base.config,\
+		86xx-hw fsl-emb-nonhw)
+
+generated_configs += mpc86xx_smp_defconfig
+mpc86xx_smp_defconfig:
+	$(call merge_into_defconfig,mpc86xx_base.config,\
+		86xx-smp 86xx-hw fsl-emb-nonhw)
+
+generated_configs += ppc32_allmodconfig
+ppc32_allmodconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/book3s_32.config \
+		-f $(srctree)/Makefile allmodconfig
+
+generated_configs += ppc44x_allmodconfig
+ppc44x_allmodconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/44x.config \
+		-f $(srctree)/Makefile allmodconfig
+
+generated_configs += ppc8xx_allmodconfig
+ppc8xx_allmodconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/8xx.config \
+		-f $(srctree)/Makefile allmodconfig
+
+generated_configs += ppc85xx_allmodconfig
+ppc85xx_allmodconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/85xx-32bit.config \
+		-f $(srctree)/Makefile allmodconfig
+
+generated_configs += ppc_defconfig
+ppc_defconfig:
+	$(call merge_into_defconfig,book3s_32.config,)
+
+generated_configs += ppc64le_allmodconfig
+ppc64le_allmodconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/le.config \
+		-f $(srctree)/Makefile allmodconfig
+
+generated_configs += ppc64le_allnoconfig
+ppc64le_allnoconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/ppc64le.config \
+		-f $(srctree)/Makefile allnoconfig
+
+generated_configs += ppc64_book3e_allmodconfig
+ppc64_book3e_allmodconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/85xx-64bit.config \
+		-f $(srctree)/Makefile allmodconfig
+
+generated_configs += ppc32_randconfig
+ppc32_randconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/32-bit.config \
+		-f $(srctree)/Makefile randconfig
+
+generated_configs += ppc64_randconfig
+ppc64_randconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/powerpc/configs/64-bit.config \
+		-f $(srctree)/Makefile randconfig
+
+PHONY += $(generated_configs)
+
+define archhelp
+  echo '* zImage          - Build default images selected by kernel config'
+  echo '  zImage.*        - Compressed kernel image (arch/powerpc/boot/zImage.*)'
+  echo '  uImage          - U-Boot native image format'
+  echo '  cuImage.<dt>    - Backwards compatible U-Boot image for older'
+  echo '                    versions which do not support device trees'
+  echo '  dtbImage.<dt>   - zImage with an embedded device tree blob'
+  echo '  simpleImage.<dt> - Firmware independent image.'
+  echo '  treeImage.<dt>  - Support for older IBM 4xx firmware (not U-Boot)'
+  echo '  install         - Install kernel using'
+  echo '                    (your) ~/bin/$(INSTALLKERNEL) or'
+  echo '                    (distribution) /sbin/$(INSTALLKERNEL) or'
+  echo '                    install to $$(INSTALL_PATH)'
+  echo '  *_defconfig     - Select default config from arch/powerpc/configs'
+  echo ''
+  echo '  Targets with <dt> embed a device tree blob inside the image'
+  echo '  These targets support board with firmware that does not'
+  echo '  support passing a device tree directly.  Replace <dt> with the'
+  echo '  name of a dts file from the arch/powerpc/boot/dts/ directory'
+  echo '  (minus the .dts extension).'
+  echo
+  $(foreach cfg,$(generated_configs),
+    printf "  %-27s - Build for %s\\n" $(cfg) $(subst _defconfig,,$(cfg));)
+endef
+
+PHONY += install
+install:
+	$(call cmd,install)
+
+ifeq ($(KBUILD_EXTMOD),)
+# We need to generate vdso-offsets.h before compiling certain files in kernel/.
+# In order to do that, we should use the archprepare target, but we can't since
+# asm-offsets.h is included in some files used to generate vdso-offsets.h, and
+# asm-offsets.h is built in prepare0, for which archprepare is a dependency.
+# Therefore we need to generate the header after prepare0 has been made, hence
+# this hack.
+prepare: vdso_prepare
+vdso_prepare: prepare0
+	$(if $(CONFIG_VDSO32),$(Q)$(MAKE) \
+		$(build)=arch/powerpc/kernel/vdso include/generated/vdso32-offsets.h)
+	$(if $(CONFIG_PPC64),$(Q)$(MAKE) \
+		$(build)=arch/powerpc/kernel/vdso include/generated/vdso64-offsets.h)
+endif
+
+archprepare: checkbin
+
+archheaders:
+	$(Q)$(MAKE) $(build)=arch/powerpc/kernel/syscalls all
+
+ifdef CONFIG_STACKPROTECTOR
+prepare: stack_protector_prepare
+
+PHONY += stack_protector_prepare
+stack_protector_prepare: prepare0
+ifdef CONFIG_PPC64
+	$(eval KBUILD_CFLAGS += -mstack-protector-guard=tls -mstack-protector-guard-reg=r13 \
+				-mstack-protector-guard-offset=$(shell awk '{if ($$2 == "PACA_CANARY") print $$3;}' \
+				$(objtree)/include/generated/asm-offsets.h))
+else
+	$(eval KBUILD_CFLAGS += -mstack-protector-guard=tls -mstack-protector-guard-reg=r2 \
+				-mstack-protector-guard-offset=$(shell awk '{if ($$2 == "TASK_CANARY") print $$3;}' \
+				$(objtree)/include/generated/asm-offsets.h))
+endif
+endif
+
+PHONY += checkbin
+checkbin:
+	@if test "x${CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT}" = "xy" -a \
+		"x${CONFIG_LD_IS_BFD}" = "xy" -a \
+		"${CONFIG_LD_VERSION}" = "23700" ; then \
+		echo -n '*** binutils 2.37 drops unused section symbols, which recordmcount ' ; \
+		echo 'is unable to handle.' ; \
+		echo '*** Please use a different binutils version.' ; \
+		false ; \
+	fi