How does the kernel compile zImage under the Arm architecture?

First, some segments of vmlinux are removed and the Image is generated, such as .comment.

arm-linux-objcopy -O binary -R .note -R .note.gnu.build-id -R .comment -S  vmlinux arch/arm/boot/Image
  Kernel: arch/arm/boot/Image is ready

Then use gzip to compress the image into piggy.gz.

gzip -f -9 < arch/arm/boot/compressed/../Image > arch/arm/boot/compressed/piggy.gz
  GZIP    arch/arm/boot/compressed/piggy.gz

Why is the generated piggy.o so long? First, compile piggy.o from piggy.S.

arm-linux-gcc -Wp,-MD,arch/arm/boot/compressed/.piggy.o.d  -nostdinc -isystem

/home/wyang2/test/usr/local/arm/4.4.1/bin/../lib/gcc/arm-none-linux-gnueabi/4.4.1/include -D__KERNEL__ -Iinclude  -I/home/wyang2/test/linux-2.6.28.6/arch/arm/include -include include/linux/autoconf.h -mlittle-endian

-Iarch/arm/mach-s3c6400/include -Iarch/arm/mach-s3c6410/include -Iarch/arm/plat-s3c64xx/include

-Iarch/arm/plat-s3c/include -D__ASSEMBLY__ -mabi=aapcs-linux -mno-thumb-interwork -D__LINUX_ARM_ARCH__=6 -march=armv6k -mtune=arm1136j-s -msoft-float -gdwarf-2  -Wa,-march=all   -c -o arch/arm/boot/compressed/piggy.o arch/arm/boot/compressed/piggy.S

 AS      arch/arm/boot/compressed/piggy.o

I have never found the relationship between piggy.o and piggy.gz. It turns out that it is in the piggy.S file. It includes the entire piggy.gz. How arrogant!

.section .piggydata,#alloc

.globl input_data

input_data:

.incbin "arch/arm/boot/compressed/piggy.gz"

.globl input_data_end

input_data_end:
下面是编译head.o， 没有看出有什么特别的地方
arm-linux-gcc -Wp,-MD,arch/arm/boot/compressed/.head.o.d -nostdinc -isystem 

/home/wyang2/test/usr/local/arm/4.4.1/bin/../lib/gcc/arm-none-linux-gnueabi/4.4.1/include -D__KERNEL__ 
-Iinclude -I/home/wyang2/test/linux-2.6.28.6/arch/arm/include -include include/linux/autoconf.h 
-mlittle-endian -Iarch/arm/mach-s3c6400/include -Iarch/arm/mach-s3c6410/include -Iarch/arm/plat-s3c64xx/include 
-Iarch/arm/plat-s3c/include -D__ASSEMBLY__ -mabi=aapcs-linux -mno-thumb-interwork 
-D__LINUX_ARM_ARCH__=6 -march=armv6k -mtune=arm1136j-s -msoft-float -gdwarf-2 -Wa,-march=all 
-c -o arch/arm/boot/compressed/head.o arch/arm/boot/compressed/head.S
AS arch/arm/boot/compressed/head.o

下面是编译misc.o 这个老长了
arm-linux-gcc -Wp,-MD,arch/arm/boot/compressed/.misc.o.d -nostdinc -isystem 

/home/wyang2/test/usr/local/arm/4.4.1/bin/../lib/gcc/arm-none-linux-gnueabi/4.4.1/include 

-D__KERNEL__ -Iinclude -I/home/wyang2/test/linux-2.6.28.6/arch/arm/include 

-include include/linux/autoconf.h -mlittle-endian -Iarch/arm/mach-s3c6400/include 

-Iarch/arm/mach-s3c6410/include -Iarch/arm/plat-s3c64xx/include -Iarch/arm/plat-s3c/include

-Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common 

-Werror-implicit-function-declaration -Os -marm -fno-omit-frame-pointer -mapcs -mno-sched-prolog 
-mabi=aapcs-linux -mno-thumb-interwork -D__LINUX_ARM_ARCH__=6 -march=armv6k -mtune=arm1136j-s 
-msoft-float -Uarm -Wframe-larger-than=1024 -fno-stack-protector -fno-omit-frame-pointer 

-fno-optimize-sibling-calls -g -Wdeclaration-after-statement -Wno-pointer-sign -fpic -fno-builtin -Dstatic= 

-D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(misc)" -D"KBUILD_MODNAME=KBUILD_STR(misc)" 

-c -o arch/arm/boot/compressed/misc.o arch/arm/boot/compressed/misc.c
;

CC arch/arm/boot/compressed/misc.o

Compile into compressed/vmlinux according to head.o piggy.o misc.o

 arm-linux-ld -EL    --defsym zreladdr=0x50008000 --defsym params_phys=0x50000100 -p --no-undefined -X /usr/local/arm/4.4.1/bin/../lib/gcc/arm-none-linux-gnueabi/4.4.1/libgcc.a -T arch/arm/boot/compressed/vmlinux.lds arch/arm/boot/compressed/head.o arch/arm/boot/compressed/piggy.o arch/arm/boot/compressed/misc.o -o arch/arm/boot/compressed/vmlinux 
  LD      arch/arm/boot/compressed/vmlinux

#@make -f scripts/Makefile.build obj=arch/arm/boot/compressed arch/arm/boot/compressed/vmlinux

Use vmlinux to remove some symbols and generate zImage.

arm-linux-objcopy -O binary -R .note -R .note.gnu.build-id -R .comment -S  arch/arm/boot/compressed/vmlinux arch/arm/boot/zImage