On Sun, 25 Sep 2022 03:19:15 +0900 Masahiro Yamada wrote:
> 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>
> ---

Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

(sorry for the sending this one so late, it got lost yesterday.)

> (no changes since v1)
> 
>  Documentation/kbuild/makefiles.rst |  9 ++---
>  Makefile                           |  4 +--
>  arch/alpha/Makefile                |  2 --
>  arch/arc/Makefile                  |  2 --
>  arch/arm/Makefile                  |  3 --
>  arch/arm64/Makefile                |  3 --
>  arch/csky/Makefile                 |  2 --
>  arch/hexagon/Makefile              |  2 --
>  arch/ia64/Makefile                 |  1 -
>  arch/loongarch/Makefile            |  2 --
>  arch/m68k/Makefile                 |  9 -----
>  arch/microblaze/Makefile           |  1 -
>  arch/mips/Makefile                 |  2 --
>  arch/nios2/Makefile                |  1 -
>  arch/openrisc/Makefile             |  2 --
>  arch/parisc/Makefile               |  2 --
>  arch/powerpc/Makefile              | 12 -------
>  arch/riscv/Makefile                |  2 --
>  arch/s390/Makefile                 |  2 --
>  arch/sh/Makefile                   |  2 --
>  arch/sparc/Makefile                |  2 --
>  arch/x86/Makefile                  |  5 ---
>  arch/xtensa/Makefile               |  2 --
>  scripts/head-object-list.txt       | 53 ++++++++++++++++++++++++++++++
>  24 files changed, 60 insertions(+), 67 deletions(-)
>  create mode 100644 scripts/head-object-list.txt
> 
> diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
> index 5a6a8426cc97..60134ddf3db1 100644
> --- a/Documentation/kbuild/makefiles.rst
> +++ b/Documentation/kbuild/makefiles.rst
> @@ -1070,8 +1070,7 @@ When kbuild executes, the following steps are followed (roughly):
>     - 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
> @@ -1219,6 +1218,9 @@ When kbuild executes, the following steps are followed (roughly):
>  	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
> @@ -1262,8 +1264,7 @@ When kbuild executes, the following steps are followed (roughly):
>  	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.
>  
> diff --git a/Makefile b/Makefile
> index a8c19f92ac9e..ab986e4c5189 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1149,10 +1149,10 @@ quiet_cmd_ar_vmlinux.a = AR      $@
>        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) FORCE
> +vmlinux.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
>  	$(call if_changed,ar_vmlinux.a)
>  
>  vmlinux.o: autoksyms_recursive vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
> diff --git a/arch/alpha/Makefile b/arch/alpha/Makefile
> index 881cb913e23a..45158024085e 100644
> --- a/arch/alpha/Makefile
> +++ b/arch/alpha/Makefile
> @@ -36,8 +36,6 @@ cflags-y				+= $(cpuflags-y)
>  # 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
> diff --git a/arch/arc/Makefile b/arch/arc/Makefile
> index efc54f3e35e0..329400a1c355 100644
> --- a/arch/arc/Makefile
> +++ b/arch/arc/Makefile
> @@ -82,8 +82,6 @@ KBUILD_CFLAGS	+= $(cflags-y)
>  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/
>  
> diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> index 56f655deebb1..29d15c9a433e 100644
> --- a/arch/arm/Makefile
> +++ b/arch/arm/Makefile
> @@ -134,9 +134,6 @@ KBUILD_AFLAGS	+=$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y) -include asm/uni
>  
>  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
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 6d9d4a58b898..6e03f15bb041 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -133,9 +133,6 @@ ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS),y)
>    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)
> diff --git a/arch/csky/Makefile b/arch/csky/Makefile
> index 4e1d619fd5c6..0e4237e55758 100644
> --- a/arch/csky/Makefile
> +++ b/arch/csky/Makefile
> @@ -59,8 +59,6 @@ LDFLAGS += -EL
>  
>  KBUILD_AFLAGS += $(KBUILD_CFLAGS)
>  
> -head-y := arch/csky/kernel/head.o
> -
>  core-y += arch/csky/$(CSKYABI)/
>  
>  libs-y += arch/csky/lib/ \
> diff --git a/arch/hexagon/Makefile b/arch/hexagon/Makefile
> index 44312bc147d8..92d005958dfb 100644
> --- a/arch/hexagon/Makefile
> +++ b/arch/hexagon/Makefile
> @@ -32,5 +32,3 @@ KBUILD_LDFLAGS += $(ldflags-y)
>  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
> diff --git a/arch/ia64/Makefile b/arch/ia64/Makefile
> index e55c2f138656..56c4bb276b6e 100644
> --- a/arch/ia64/Makefile
> +++ b/arch/ia64/Makefile
> @@ -44,7 +44,6 @@ quiet_cmd_objcopy = OBJCOPY $@
>  cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
>  
>  KBUILD_CFLAGS += $(cflags-y)
> -head-y := arch/ia64/kernel/head.o
>  
>  libs-y				+= arch/ia64/lib/
>  
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index ec3de6191276..131fc210c2bf 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -72,8 +72,6 @@ CHECKFLAGS += $(shell $(CC) $(KBUILD_CFLAGS) -dM -E -x c /dev/null | \
>  	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),)
> diff --git a/arch/m68k/Makefile b/arch/m68k/Makefile
> index e358605b70ba..43e39040d3ac 100644
> --- a/arch/m68k/Makefile
> +++ b/arch/m68k/Makefile
> @@ -86,15 +86,6 @@ ifdef CONFIG_KGDB
>  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/
>  
>  
> diff --git a/arch/microblaze/Makefile b/arch/microblaze/Makefile
> index 1826d9ce4459..3f8a86c4336a 100644
> --- a/arch/microblaze/Makefile
> +++ b/arch/microblaze/Makefile
> @@ -48,7 +48,6 @@ CPUFLAGS-1 += $(call cc-option,-mcpu=v$(CPU_VER))
>  # r31 holds current when in kernel mode
>  KBUILD_CFLAGS += -ffixed-r31 $(CPUFLAGS-y) $(CPUFLAGS-1) $(CPUFLAGS-2)
>  
> -head-y := arch/microblaze/kernel/head.o
>  libs-y += arch/microblaze/lib/
>  
>  boot := arch/microblaze/boot
> diff --git a/arch/mips/Makefile b/arch/mips/Makefile
> index 4d2a3e73fc45..b296e33f8e33 100644
> --- a/arch/mips/Makefile
> +++ b/arch/mips/Makefile
> @@ -324,8 +324,6 @@ endif
>  
>  OBJCOPYFLAGS		+= --remove-section=.reginfo
>  
> -head-y := arch/mips/kernel/head.o
> -
>  libs-y			+= arch/mips/lib/
>  libs-$(CONFIG_MIPS_FP_SUPPORT) += arch/mips/math-emu/
>  
> diff --git a/arch/nios2/Makefile b/arch/nios2/Makefile
> index 3f34e6831863..f1ff4ce0f1a2 100644
> --- a/arch/nios2/Makefile
> +++ b/arch/nios2/Makefile
> @@ -37,7 +37,6 @@ KBUILD_CFLAGS += -DUTS_SYSNAME=\"$(UTS_SYSNAME)\"
>  KBUILD_CFLAGS += -fno-builtin
>  KBUILD_CFLAGS += -G 0
>  
> -head-y		:= arch/nios2/kernel/head.o
>  libs-y		+= arch/nios2/lib/ $(LIBGCC)
>  
>  INSTALL_PATH ?= /tftpboot
> diff --git a/arch/openrisc/Makefile b/arch/openrisc/Makefile
> index b446510173cd..68249521db5a 100644
> --- a/arch/openrisc/Makefile
> +++ b/arch/openrisc/Makefile
> @@ -55,8 +55,6 @@ ifeq ($(CONFIG_OPENRISC_HAVE_INST_SEXT),y)
>  	KBUILD_CFLAGS += $(call cc-option,-msext)
>  endif
>  
> -head-y 		:= arch/openrisc/kernel/head.o
> -
>  libs-y		+= $(LIBGCC)
>  
>  PHONY += vmlinux.bin
> diff --git a/arch/parisc/Makefile b/arch/parisc/Makefile
> index e38d993d87f2..a2d8600521f9 100644
> --- a/arch/parisc/Makefile
> +++ b/arch/parisc/Makefile
> @@ -113,8 +113,6 @@ cflags-$(CONFIG_PA7100LC)	+= -march=1.1 -mschedule=7100LC
>  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
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 02742facf895..89c27827a11f 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -226,18 +226,6 @@ KBUILD_CFLAGS += $(cpu-as-y)
>  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
>  
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 3fa8ef336822..e013df8e7b8b 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -110,8 +110,6 @@ else
>  KBUILD_IMAGE	:= $(boot)/Image.gz
>  endif
>  
> -head-y := arch/riscv/kernel/head.o
> -
>  libs-y += arch/riscv/lib/
>  libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
>  
> diff --git a/arch/s390/Makefile b/arch/s390/Makefile
> index 4cb5d17e7ead..de6d8b2ea4d8 100644
> --- a/arch/s390/Makefile
> +++ b/arch/s390/Makefile
> @@ -119,8 +119,6 @@ export KBUILD_CFLAGS_DECOMPRESSOR
>  
>  OBJCOPYFLAGS	:= -O binary
>  
> -head-y		:= arch/s390/kernel/head64.o
> -
>  libs-y		+= arch/s390/lib/
>  drivers-y	+= drivers/s390/
>  
> diff --git a/arch/sh/Makefile b/arch/sh/Makefile
> index b39412bf91fb..5c8776482530 100644
> --- a/arch/sh/Makefile
> +++ b/arch/sh/Makefile
> @@ -114,8 +114,6 @@ endif
>  
>  export ld-bfd
>  
> -head-y	:= arch/sh/kernel/head_32.o
> -
>  # Mach groups
>  machdir-$(CONFIG_SOLUTION_ENGINE)		+= mach-se
>  machdir-$(CONFIG_SH_HP6XX)			+= mach-hp6xx
> diff --git a/arch/sparc/Makefile b/arch/sparc/Makefile
> index fe58a410b4ce..a4ea5b05f288 100644
> --- a/arch/sparc/Makefile
> +++ b/arch/sparc/Makefile
> @@ -56,8 +56,6 @@ endif
>  
>  endif
>  
> -head-y                 := arch/sparc/kernel/head_$(BITS).o
> -
>  libs-y                 += arch/sparc/prom/
>  libs-y                 += arch/sparc/lib/
>  
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index bafbd905e6e7..9afd323c6916 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -234,11 +234,6 @@ archheaders:
>  ###
>  # 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
> diff --git a/arch/xtensa/Makefile b/arch/xtensa/Makefile
> index 5097caa7bf0c..bfd8e433ed62 100644
> --- a/arch/xtensa/Makefile
> +++ b/arch/xtensa/Makefile
> @@ -55,8 +55,6 @@ KBUILD_CPPFLAGS += $(patsubst %,-I$(srctree)/%include,$(vardirs) $(plfdirs))
>  
>  KBUILD_DEFCONFIG := iss_defconfig
>  
> -head-y		:= arch/xtensa/kernel/head.o
> -
>  libs-y		+= arch/xtensa/lib/
>  
>  boot		:= arch/xtensa/boot
> diff --git a/scripts/head-object-list.txt b/scripts/head-object-list.txt
> new file mode 100644
> index 000000000000..dd2ba2eda636
> --- /dev/null
> +++ b/scripts/head-object-list.txt
> @@ -0,0 +1,53 @@
> +# 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
> -- 
> 2.34.1

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