Re: [PATCH v3 7/7] kbuild: remove head-y syntax

From: Nicolas Schier
Date: Thu Sep 29 2022 - 11:22:18 EST

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In reply to: Masahiro Yamada: "[PATCH v3 7/7] kbuild: remove head-y syntax"
Next in thread: Masahiro Yamada: "[PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head"
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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@xxxxxxxxxx>
> ---

Reviewed-by: Nicolas Schier <nicolas@xxxxxxxxx>

(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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