zImage

from mkl Note
from https://hackmd.io/s/BJroQrL-g

• zImage decompression
• zImage Format
  • zImage内核镜像解压过程详解
  • Kernel Images: from building to booting

• [path to kernel]/arch/arm/boot/compressed/Makefile

LDFLAGS_vmlinux := --defsym zreladdr=$(ZRELADDR)

• [path to kernel]/arch/arm/boot/compressed/head.S

zreladdr

        .word    zreladdr        @ r4

call_kerenl

call_kernel:    bl    cache_clean_flush
        bl    cache_off
        mov    r0, #0            @ must be zero
        mov    r1, r7            @ restore architecture number
        mov    r2, r8            @ restore atags pointer
        mov    pc, r4            @ call kernel

params_phys

• [path to kernel]/arch/arm/boot/compressed/misc.c

wont_overwrite

Check to see if we will overwrite ourselves.
r4 = final kernel address
r9 = size of decompressed image
r10 = end of this image, including bss/stack/malloc space if non XIP
We basically want:
(1). r4 - 16k page directory >= r10
vmlinux的起始地址大于zImage运行时所需的最大地址（r4 - 16k）
(2). r4 + image length <= address of wont_overwrite
zImage的起始地址大于vmlinux的目标起始地址加上vmlinux大小（r9）
(3). Relocate ourselves past the end of the decompressed kernel.
vmlinux的目标位置刚好和zImage的当前位置重合，所以解决方案就是先将zImage解压到zImage的上面，再将其重定位或者说搬移到目标位置。

• *****解压缩内核,分三种情况，下面一一解释：

decompress_kernel