Kbuild puts the objects listed in head-y at the head of vmlinux.
Conventionally, we do this for head*.S, which contains the kernel entry
point.
A counter approach is to control the section order by the linker script.
Actually, the code marked as __HEAD goes into the ".head.text" section,
which is placed before the normal ".text" section.
I do not know if both of them are needed. From the build system
perspective, head-y is not mandatory. If you can achieve the proper code
placement by the linker script only, it would be cleaner.
I collected the current head-y objects into head-object-list.txt. It is
a whitelist. My hope is it will be reduced in the long run.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
- The values of the above variables are expanded in arch/$(SRCARCH)/Makefile.
5) All object files are then linked and the resulting file vmlinux is
located at the root of the obj tree.
- The very first objects linked are listed in head-y, assigned by
- arch/$(SRCARCH)/Makefile.
+ The very first objects linked are listed in scripts/head-object-list.txt.
6) Finally, the architecture-specific part does any required post processing
and builds the final bootimage.
- This includes building boot records
All object files for vmlinux. They are linked to vmlinux in the same
order as listed in KBUILD_VMLINUX_OBJS.
+ The objects listed in scripts/head-object-list.txt are exceptions;
+ they are placed before the other objects.
+
KBUILD_VMLINUX_LIBS
All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and
machinery is all architecture-independent.
- head-y, core-y, libs-y, drivers-y
- $(head-y) lists objects to be linked first in vmlinux.
+ core-y, libs-y, drivers-y
$(libs-y) lists directories where a lib.a archive can be located.
cmd_ar_vmlinux.a = \
rm -f $@; \
$(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
- $(AR) mPiT $$($(AR) t $@ | head -n1) $@ $(head-y)
+ $(AR) mPiT $$($(AR) t $@ | head -n1) $@ $$($(AR) t $@ | grep -F --file=$(srctree)/scripts/head-object-list.txt)
targets += vmlinux.a
-vmlinux.a: $(KBUILD_VMLINUX_OBJS) autoksyms_recursive FORCE
+vmlinux.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt autoksyms_recursive FORCE
$(call if_changed,ar_vmlinux.a)
vmlinux.o: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
# BWX is most important, but we don't really want any emulation ever.
KBUILD_CFLAGS += $(cflags-y) -Wa,-mev6
-head-y := arch/alpha/kernel/head.o
-
libs-y += arch/alpha/lib/
# export what is needed by arch/alpha/boot/Makefile
KBUILD_AFLAGS += $(KBUILD_CFLAGS)
KBUILD_LDFLAGS += $(ldflags-y)
-head-y := arch/arc/kernel/head.o
-
# w/o this dtb won't embed into kernel binary
core-y += arch/arc/boot/dts/
CHECKFLAGS += -D__arm__
-#Default value
-head-y := arch/arm/kernel/head$(MMUEXT).o
-
# Text offset. This list is sorted numerically by address in order to
# provide a means to avoid/resolve conflicts in multi-arch kernels.
# Note: the 32kB below this value is reserved for use by the kernel
CC_FLAGS_FTRACE := -fpatchable-function-entry=2
endif
-# Default value
-head-y := arch/arm64/kernel/head.o
-
ifeq ($(CONFIG_KASAN_SW_TAGS), y)
KASAN_SHADOW_SCALE_SHIFT := 4
else ifeq ($(CONFIG_KASAN_GENERIC), y)
KBUILD_AFLAGS += $(KBUILD_CFLAGS)
-head-y := arch/csky/kernel/head.o
-
core-y += arch/csky/$(CSKYABI)/
libs-y += arch/csky/lib/ \
TIR_NAME := r19
KBUILD_CFLAGS += -ffixed-$(TIR_NAME) -DTHREADINFO_REG=$(TIR_NAME) -D__linux__
KBUILD_AFLAGS += -DTHREADINFO_REG=$(TIR_NAME)
-
-head-y := arch/hexagon/kernel/head.o
cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
KBUILD_CFLAGS += $(cflags-y)
-head-y := arch/ia64/kernel/head.o
libs-y += arch/ia64/lib/
sed -e "s/^\#define /-D'/" -e "s/ /'='/" -e "s/$$/'/" -e 's/\$$/&&/g')
endif
-head-y := arch/loongarch/kernel/head.o
-
libs-y += arch/loongarch/lib/
ifeq ($(KBUILD_EXTMOD),)
KBUILD_CFLAGS := $(subst -fomit-frame-pointer,,$(KBUILD_CFLAGS)) -g
endif
-#
-# Select the assembler head startup code. Order is important. The default
-# head code is first, processor specific selections can override it after.
-#
-head-y := arch/m68k/kernel/head.o
-head-$(CONFIG_SUN3) := arch/m68k/kernel/sun3-head.o
-head-$(CONFIG_M68000) := arch/m68k/68000/head.o
-head-$(CONFIG_COLDFIRE) := arch/m68k/coldfire/head.o
-
libs-y += arch/m68k/lib/
# r31 holds current when in kernel mode
KBUILD_CFLAGS += -ffixed-r31 $(CPUFLAGS-y) $(CPUFLAGS-1) $(CPUFLAGS-2)
-head-y := arch/microblaze/kernel/head.o
libs-y += arch/microblaze/lib/
boot := arch/microblaze/boot
OBJCOPYFLAGS += --remove-section=.reginfo
-head-y := arch/mips/kernel/head.o
-
libs-y += arch/mips/lib/
libs-$(CONFIG_MIPS_FP_SUPPORT) += arch/mips/math-emu/
KBUILD_CFLAGS += -fno-builtin
KBUILD_CFLAGS += -G 0
-head-y := arch/nios2/kernel/head.o
libs-y += arch/nios2/lib/ $(LIBGCC)
INSTALL_PATH ?= /tftpboot
KBUILD_CFLAGS += $(call cc-option,-msext)
endif
-head-y := arch/openrisc/kernel/head.o
-
libs-y += $(LIBGCC)
PHONY += vmlinux.bin
cflags-$(CONFIG_PA7300LC) += -march=1.1 -mschedule=7300
cflags-$(CONFIG_PA8X00) += -march=2.0 -mschedule=8000
-head-y := arch/parisc/kernel/head.o
-
KBUILD_CFLAGS += $(cflags-y)
LIBGCC := $(shell $(CC) -print-libgcc-file-name)
export LIBGCC
KBUILD_AFLAGS += $(aflags-y)
KBUILD_CFLAGS += $(cflags-y)
-head-$(CONFIG_PPC64) := arch/powerpc/kernel/head_64.o
-head-$(CONFIG_PPC_BOOK3S_32) := arch/powerpc/kernel/head_book3s_32.o
-head-$(CONFIG_PPC_8xx) := arch/powerpc/kernel/head_8xx.o
-head-$(CONFIG_40x) := arch/powerpc/kernel/head_40x.o
-head-$(CONFIG_44x) := arch/powerpc/kernel/head_44x.o
-head-$(CONFIG_FSL_BOOKE) := arch/powerpc/kernel/head_fsl_booke.o
-
-head-$(CONFIG_PPC64) += arch/powerpc/kernel/entry_64.o
-head-$(CONFIG_PPC_FPU) += arch/powerpc/kernel/fpu.o
-head-$(CONFIG_ALTIVEC) += arch/powerpc/kernel/vector.o
-head-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE) += arch/powerpc/kernel/prom_init.o
-
# Default to zImage, override when needed
all: zImage
KBUILD_IMAGE := $(boot)/Image.gz
endif
-head-y := arch/riscv/kernel/head.o
-
libs-y += arch/riscv/lib/
libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
OBJCOPYFLAGS := -O binary
-head-y := arch/s390/kernel/head64.o
-
libs-y += arch/s390/lib/
drivers-y += drivers/s390/
export ld-bfd
-head-y := arch/sh/kernel/head_32.o
-
# Mach groups
machdir-$(CONFIG_SOLUTION_ENGINE) += mach-se
machdir-$(CONFIG_SH_HP6XX) += mach-hp6xx
endif
-head-y := arch/sparc/kernel/head_$(BITS).o
-
libs-y += arch/sparc/prom/
libs-y += arch/sparc/lib/
###
# Kernel objects
-head-y := arch/x86/kernel/head_$(BITS).o
-head-y += arch/x86/kernel/head$(BITS).o
-head-y += arch/x86/kernel/ebda.o
-head-y += arch/x86/kernel/platform-quirks.o
-
libs-y += arch/x86/lib/
# drivers-y are linked after core-y
KBUILD_DEFCONFIG := iss_defconfig
-head-y := arch/xtensa/kernel/head.o
-
libs-y += arch/xtensa/lib/
boot := arch/xtensa/boot
--- /dev/null
+# Head objects
+#
+# The objects listed here are placed at the head of vmlinux. A typical use-case
+# is an object that contains the entry point. This is kept for compatibility
+# with head-y, which Kbuild used to support.
+#
+# A counter approach is to control the section placement by the linker script.
+# The code marked as __HEAD goes into the ".head.text" section, which is placed
+# before the normal ".text" section.
+#
+# If you can achieve the correct code ordering by linker script, please delete
+# the entry from this file.
+#
+arch/alpha/kernel/head.o
+arch/arc/kernel/head.o
+arch/arm/kernel/head-nommu.o
+arch/arm/kernel/head.o
+arch/arm64/kernel/head.o
+arch/csky/kernel/head.o
+arch/hexagon/kernel/head.o
+arch/ia64/kernel/head.o
+arch/loongarch/kernel/head.o
+arch/m68k/68000/head.o
+arch/m68k/coldfire/head.o
+arch/m68k/kernel/head.o
+arch/m68k/kernel/sun3-head.o
+arch/microblaze/kernel/head.o
+arch/mips/kernel/head.o
+arch/nios2/kernel/head.o
+arch/openrisc/kernel/head.o
+arch/parisc/kernel/head.o
+arch/powerpc/kernel/head_40x.o
+arch/powerpc/kernel/head_44x.o
+arch/powerpc/kernel/head_64.o
+arch/powerpc/kernel/head_8xx.o
+arch/powerpc/kernel/head_book3s_32.o
+arch/powerpc/kernel/head_fsl_booke.o
+arch/powerpc/kernel/entry_64.o
+arch/powerpc/kernel/fpu.o
+arch/powerpc/kernel/vector.o
+arch/powerpc/kernel/prom_init.o
+arch/riscv/kernel/head.o
+arch/s390/kernel/head64.o
+arch/sh/kernel/head_32.o
+arch/sparc/kernel/head_32.o
+arch/sparc/kernel/head_64.o
+arch/x86/kernel/head_32.o
+arch/x86/kernel/head_64.o
+arch/x86/kernel/head32.o
+arch/x86/kernel/head64.o
+arch/x86/kernel/ebda.o
+arch/x86/kernel/platform-quirks.o
+arch/xtensa/kernel/head.o
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