基於Linux2.6.38.8內核zImage文件的自解壓詳解

Linux內核編譯完成後會生成zImage內核鏡像文件。zImage是如何解壓的呢？本文將結合關鍵代碼，講解zImage的解壓過程。還是先來看看zImage的組成吧。在內核編譯完成後會在arch/arm/boot/下生成zImage。

在arch/arm/boot/Makefile中，如下代碼：

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1. #
2. # arch/arm/boot/Makefile
3. #
4. # This file is included by the global makefile so that you can add your own
5. # architecture-specific flags and dependencies.
6. #
7. # This file is subject to the terms and conditions of the GNU General Public
8. # License. See the file "COPYING" in the main directory of this archive
9. # for more details.
10. #
11. # Copyright (C) 1995-2002 Russell King
12. #
14. MKIMAGE := $(srctree)/scripts/mkuboot.sh
16. ifneq ($(MACHINE),)
17. include $(srctree)/$(MACHINE)/Makefile.boot
18. endif
20. # Note: the following conditions must always be true:
21. # ZRELADDR == virt_to_phys(PAGE_OFFSET + TEXT_OFFSET)
22. # PARAMS_PHYS must be within 4MB of ZRELADDR
23. # INITRD_PHYS must be in RAM
24. ZRELADDR := $(zreladdr-y)
25. PARAMS_PHYS := $(params_phys-y)
26. INITRD_PHYS := $(initrd_phys-y)
28. export ZRELADDR INITRD_PHYS PARAMS_PHYS
30. targets := Image zImage xipImage bootpImage uImage
32. ifeq ($(CONFIG_XIP_KERNEL),y)
34. $(obj)/xipImage: vmlinux FORCE
35. $(call if_changed,objcopy)
36. @echo ' Kernel: $@ is ready (physical address: $(CONFIG_XIP_PHYS_ADDR))'
38. $(obj)/Image $(obj)/zImage: FORCE
39. @echo 'Kernel configured for XIP (CONFIG_XIP_KERNEL=y)'
40. @echo 'Only the xipImage target is available in this case'
41. @false
43. else
45. $(obj)/xipImage: FORCE
46. @echo 'Kernel not configured for XIP (CONFIG_XIP_KERNEL!=y)'
47. @false
49. $(obj)/Image: vmlinux FORCE
50. $(call if_changed,objcopy)
51. @echo ' Kernel: $@ is ready'
53. $(obj)/compressed/vmlinux: $(obj)/Image FORCE
54. $(Q)$(MAKE) $(build)=$(obj)/compressed $@
56. $(obj)/zImage: $(obj)/compressed/vmlinux FORCE
57. $(call if_changed,objcopy)
58. @echo ' Kernel: $@ is ready'
60. endif
62. quiet_cmd_uimage = UIMAGE $@
63. cmd_uimage = $(CONFIG_SHELL) $(MKIMAGE) -A arm -O linux -T kernel \
64. -C none -a $(LOADADDR) -e $(STARTADDR) \
65. -n 'Linux-$(KERNELRELEASE)' -d {1}lt; $@
67. ifeq ($(CONFIG_ZBOOT_ROM),y)
68. $(obj)/uImage: LOADADDR=$(CONFIG_ZBOOT_ROM_TEXT)
69. else
70. $(obj)/uImage: LOADADDR=$(ZRELADDR)
71. endif
73. $(obj)/uImage: STARTADDR=$(LOADADDR)
75. $(obj)/uImage: $(obj)/zImage FORCE
76. $(call if_changed,uimage)
77. @echo ' Image $@ is ready'
79. $(obj)/bootp/bootp: $(obj)/zImage initrd FORCE
80. $(Q)$(MAKE) $(build)=$(obj)/bootp $@
81. @:
83. $(obj)/bootpImage: $(obj)/bootp/bootp FORCE
84. $(call if_changed,objcopy)
85. @echo ' Kernel: $@ is ready'
87. PHONY += initrd FORCE
88. initrd:
89. @test "$(INITRD_PHYS)" != "" || \
90. (echo This machine does not support INITRD; exit -1)
91. @test "$(INITRD)" != "" || \
92. (echo You must specify INITRD; exit -1)
94. install: $(obj)/Image
95. $(CONFIG_SHELL) $(srctree)/$(src)/install.sh $(KERNELRELEASE) \
96. $(obj)/Image System.map "$(INSTALL_PATH)"
98. zinstall: $(obj)/zImage
99. $(CONFIG_SHELL) $(srctree)/$(src)/install.sh $(KERNELRELEASE) \
100. $(obj)/zImage System.map "$(INSTALL_PATH)"
102. zi:
103. $(CONFIG_SHELL) $(srctree)/$(src)/install.sh $(KERNELRELEASE) \
104. $(obj)/zImage System.map "$(INSTALL_PATH)"
106. i:
107. $(CONFIG_SHELL) $(srctree)/$(src)/install.sh $(KERNELRELEASE) \
108. $(obj)/Image System.map "$(INSTALL_PATH)"
110. subdir- := bootp compressed