[PATCH v2 8/8] kbuild: remove head-y syntax

Masahiro Yamada
2022-09-06T06:14:20Z

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>
---

(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 07c7e5a843c1..528c54d56c09 100644
--- a/Documentation/kbuild/makefiles.rst
+++ b/Documentation/kbuild/makefiles.rst
@@ -1065,8 +1065,7 @@ 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
@@ -1214,6 +1213,9 @@ 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
@@ -1257,8 +1259,7 @@ 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 f2d06aaaefd3..e96ee00609b7 100644
--- a/Makefile
+++ b/Makefile
@@ -1155,10 +1155,10 @@ quiet_cmd_ar_vmlinux.a = AR $@
cmd_ar_vmlinux.a = \
rm -f $@; \
$(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
- $(AR) mPi $$($(AR) t $@ | head -n1) $@ $(head-y)
+ $(AR) mPi $$($(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)

targets += vmlinux.o
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