mkimage工具是u-boot用来制作镜像文件的工具，其源代码在u-boot源码的tools目录下：mkimage.c。我们使用bootm命令加载的内核和根文件系统，都要用这个工具加上个头。
我们首先看下这个头的结构（一共64B）：
typedef struct image_header {
uint32_t ih_magic; /* Image Header Magic Number */
uint32_t ih_hcrc; /* Image Header CRC Checksum */
uint32_t ih_time; /* Image Creation Timestamp */
uint32_t ih_size; /* Image Data Size */
uint32_t ih_load; /* Data Load Address */
uint32_t ih_ep; /* Entry Point Address */
uint32_t ih_dcrc; /* Image Data CRC Checksum */
uint8_t ih_os; /* Operating System */
uint8_t ih_arch; /* CPU architecture */
uint8_t ih_type; /* Image Type */
uint8_t ih_comp; /* Compression Type */
uint8_t ih_name[IH_NMLEN]; /* Image Name */
} image_header_t;
我们再看下上面哪些参数是需要我们传递给mkimage这个工具?下面是这个工具使用说明
[root@localhost linux]# mkimage
Usage: mkimage -l image
-l ==> list image header information
mkimage [-x] -A arch -O os -T type -C comp -a addr -e ep -n name -d data_file[:data_file...] image
-A ==> set architecture to 'arch'
-O ==> set operating system to 'os'
-T ==> set image type to 'type'
-C ==> set compression type 'comp'
-a ==> set load address to 'addr' (hex)
-e ==> set entry point to 'ep' (hex)
-n ==> set image name to 'name'
-d ==> use image data from 'datafile'
-x ==> set XIP (execute in place)
[root@localhost linux]#
-A：CPU 架构，可选的值有：
"alpha","arm","x86","ia64","m6k8","microblaze","mips","mips64","nios","nios2","ppc","s390","sh","sparc","sparc64",
"blackfin","avr32"。
-O：操作系统。可选的值有：
"4_4bsd","artos","esix","freebsd","irix","linux","lynxos","ncr","netbsd","openbsd","psos","qnx","rtems","sco","sloaris",
"u-boot",vxworks"
-T：镜像类型。可选的值有：
"filesystem","firmware","firmware","kernel","multi","ramdisk","script","standalone","flat_dt"
-C：镜像压缩类型。可选的值有：
"none","bzip2","gzip" none为没有压缩。
-n： 镜像名称。最长32个字符。
-a：镜像加载地址（16进制）
-e：镜像入口（16进制）
-d：制定制作镜像的源文件。
-x是指就在此执行的意思，就是说 入口 = 加载地址+64。