bootm命令執行過程中調用了bootm_start函數,這個函數比較重要,所以先分析它。
1.common/cmd_bootm.c
- static int bootm_start(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
- {
- void *os_hdr;
- int ret;
- memset ((void *)&images, 0, sizeof (images));//images是一個bootm_headers_t類型的全局變量。見下面的分析。
- images.verify = getenv_yesno ("verify");//從環境變量中檢查是否要對鏡像的數據(不是鏡像頭)進行校驗。
- bootm_start_lmb();//不做任何有意義的工作,除了定義# define lmb_reserve(lmb, base, size)
- /* get kernel image header, start address and length */尋找可用的內核鏡像,見下面的分析。主要根據傳入的參數檢查鏡像的合法性並獲取信息。
- os_hdr = boot_get_kernel (cmdtp, flag, argc, argv,
- &images, &images.os.image_start, &images.os.image_len);//返回指向內存中鏡像頭的指針
- if (images.os.image_len == 0) {
- puts ("ERROR: can't get kernel image!/n");
- return 1;
- }
- /* get image parameters */
- switch (genimg_get_format (os_hdr)) {//根據鏡像魔數獲取鏡像類型
- case IMAGE_FORMAT_LEGACY:
- images.os.type = image_get_type (os_hdr);//鏡像類型
- images.os.comp = image_get_comp (os_hdr);//壓縮類型
- images.os.os = image_get_os (os_hdr);//操作系統類型
- images.os.end = image_get_image_end (os_hdr);//當前鏡像的尾地址
- images.os.load = image_get_load (os_hdr);//鏡像數據的載入地址
- break;
- default:
- puts ("ERROR: unknown image format type!/n");
- return 1;
- }
- /* find kernel entry point */
- if (images.legacy_hdr_valid) {//如果鏡像已經通過驗證
- images.ep = image_get_ep (&images.legacy_hdr_os_copy);//獲取入口地址,填充images.ep 。
- } else {
- puts ("Could not find kernel entry point!/n");
- return 1;
- }
- if (((images.os.type == IH_TYPE_KERNEL) ||
- (images.os.type == IH_TYPE_MULTI)) &&
- (images.os.os == IH_OS_LINUX)) {
- /* find ramdisk */3250的配置中這個函數不做任何工作
- ret = boot_get_ramdisk (argc, argv, &images, IH_INITRD_ARCH,
- &images.rd_start, &images.rd_end);
- if (ret) {
- puts ("Ramdisk image is corrupt or invalid/n");
- return 1;
- }
- }
- images.os.start = (ulong)os_hdr;//指向內存中鏡像的頭地址
- images.state = BOOTM_STATE_START;//標記引導狀態
- return 0;
- }
總結一下這個函數的主要工作:第一步校驗鏡像的正確性,獲取鏡像的信息(根據鏡像頭),第二部將第一步獲取的信息存入images(主要是填充image_info_t類型的os成員)
2. bootm_headers_t
- typedef struct bootm_headers {
- /*
- * Legacy os image header, if it is a multi component image
- * then boot_get_ramdisk() and get_fdt() will attempt to get
- * data from second and third component accordingly.
- */
- image_header_t *legacy_hdr_os; /* image header pointer */
- image_header_t legacy_hdr_os_copy; /* header copy */
- ulong legacy_hdr_valid;
- #ifndef USE_HOSTCC
- image_info_t os; /* os image info */
- ulong ep; /* entry point of OS */
- ulong rd_start, rd_end;/* ramdisk start/end */
- ulong ft_len; /* length of flat device tree */
- ulong initrd_start;
- ulong initrd_end;
- ulong cmdline_start;
- ulong cmdline_end;
- bd_t *kbd;
- #endif
- int verify; /* getenv("verify")[0] != 'n' */
- #define BOOTM_STATE_START (0x00000001)
- #define BOOTM_STATE_LOADOS (0x00000002)
- #define BOOTM_STATE_RAMDISK (0x00000004)
- #define BOOTM_STATE_FDT (0x00000008)
- #define BOOTM_STATE_OS_CMDLINE (0x00000010)
- #define BOOTM_STATE_OS_BD_T (0x00000020)
- #define BOOTM_STATE_OS_PREP (0x00000040)
- #define BOOTM_STATE_OS_GO (0x00000080)
- int state;
- } bootm_headers_t;
- /*
- * Legacy format image header,
- * all data in network byte order (aka natural aka bigendian).
- */內核鏡像頭 include/image.h
- typedef struct image_header {
- uint32_t ih_magic; /* Image Header Magic Number */鏡像頭部幻數,為#define IH_MAGIC 0x27051956
- uint32_t ih_hcrc; /* Image Header CRC Checksum */鏡像頭部crc校驗碼
- uint32_t ih_time; /* Image Creation Timestamp */鏡像創建時間戳
- uint32_t ih_size; /* Image Data Size */鏡像數據大小(不算頭部)1828536
- uint32_t ih_load; /* Data Load Address */數據將要載入的內存地址 80008000
- uint32_t ih_ep; /* Entry Point Address */鏡像入口地址 80008000
- uint32_t ih_dcrc; /* Image Data CRC Checksum */鏡像數據校驗碼
- uint8_t ih_os; /* Operating System */操作系統類型 #define IH_OS_LINUX 5
- uint8_t ih_arch; /* CPU architecture */CPU架構類型 #define IH_ARCH_ARM 2
- uint8_t ih_type; /* Image Type */鏡像類型 IH_TYPE_KERNEL
- uint8_t ih_comp; /* Compression Type */壓縮類型 IH_COMP_NONE
- uint8_t ih_name[IH_NMLEN]; /* Image Name */鏡像名字Linux-2.6.27.8,#define IH_NMLEN 32
- } image_header_t;
- 鏡像信息 include/image.h
- typedef struct image_info {
- ulong start, end; /* start/end of blob */鏡像的起始地址和尾地址
- ulong image_start, image_len; /* start of image within blob, len of image */鏡像數據的開始地址和長度
- ulong load; /* load addr for the image */鏡像數據的裝載地址
- uint8_t comp, type, os; /* compression, type of image, os type */壓縮類型,鏡像類型和操作系統類型
- } image_info_t;
3。boot_get_kernel
- /**
- * boot_get_kernel - find kernel image
- * @os_data: pointer to a ulong variable, will hold os data start address
- * @os_len: pointer to a ulong variable, will hold os data length
- *
- * boot_get_kernel() tries to find a kernel image, verifies its integrity
- * and locates kernel data.
- *
- * returns:
- * pointer to image header if valid image was found, plus kernel start
- * address and length, otherwise NULL
- */
- 尋找可用的內核鏡像
- static void *boot_get_kernel (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
- bootm_headers_t *images, ulong *os_data, ulong *os_len)
- {
- image_header_t *hdr;
- ulong img_addr;
- /* find out kernel image address */
- if (argc < 2) {//如果參數太少
- img_addr = load_addr; //使用默認的鏡像載入地址,這個地址是在配置頭文件中定義的 ulong load_addr = CONFIG_SYS_LOAD_ADDR;
- debug ("* kernel: default image load address = 0x%08lx/n",
- load_addr);
- } else {
- img_addr = simple_strtoul(argv[1], NULL, 16);//參數足夠的話,把第二個參數轉化為16進制作為地址
- debug ("* kernel: cmdline image address = 0x%08lx/n", img_addr);
- }
- show_boot_progress (1);
- /* copy from dataflash if needed */
- img_addr = genimg_get_image (img_addr);//對於3250,這個函數什麼都沒做。因為沒有dataflash.
- /* check image type, for FIT images get FIT kernel node */
- *os_data = *os_len = 0;
- switch (genimg_get_format ((void *)img_addr)) {//根據上面得到的鏡像的地址,獲取鏡像的類型。這個函數根據鏡像頭部的魔數返回類型。
- case IMAGE_FORMAT_LEGACY:
- printf ("## Booting kernel from Legacy Image at %08lx .../n", //打印引導消息
- img_addr);
- hdr = image_get_kernel (img_addr, images->verify);//檢驗鏡像的合法性(校驗碼、魔數、架構類型等),並打印信息。見下面的分析。
- if (!hdr)
- return NULL;
- show_boot_progress (5);
- /* get os_data and os_len */
- switch (image_get_type (hdr)) {
- case IH_TYPE_KERNEL:
- *os_data = image_get_data (hdr);//鏡像數據的地址,也就是緊挨著鏡像頭的地址。
- *os_len = image_get_data_size (hdr);//鏡像數據部分大小
- break;
- case IH_TYPE_MULTI:
- image_multi_getimg (hdr, 0, os_data, os_len);
- break;
- case IH_TYPE_STANDALONE:
- *os_data = image_get_data (hdr);
- *os_len = image_get_data_size (hdr);
- break;
- default:
- printf ("Wrong Image Type for %s command/n", cmdtp->name);
- show_boot_progress (-5);
- return NULL;
- }
- /*
- * copy image header to allow for image overwrites during kernel
- * decompression.
- */拷貝一份鏡像的頭部到images中。
- memmove (&images->legacy_hdr_os_copy, hdr, sizeof(image_header_t));
- /* save pointer to image header */
- images->legacy_hdr_os = hdr;//images中指針指向鏡像的頭部
- images->legacy_hdr_valid = 1;//鏡像已經檢驗合格,置標志量
- show_boot_progress (6);
- break;
- default:
- printf ("Wrong Image Format for %s command/n", cmdtp->name);
- show_boot_progress (-108);
- return NULL;
- }
- debug (" kernel data at 0x%08lx, len = 0x%08lx (%ld)/n",
- *os_data, *os_len, *os_len);
- return (void *)img_addr;
- }
4。image_get_kernel
- common/cmd_bootm.c
- static image_header_t *image_get_kernel (ulong img_addr, int verify)
- {
- image_header_t *hdr = (image_header_t *)img_addr;
- if (!image_check_magic(hdr)) { //檢查鏡像頭部的魔數是否等於 IH_MAGIC
- puts ("Bad Magic Number/n");
- show_boot_progress (-1);
- return NULL;
- }
- show_boot_progress (2);
- if (!image_check_hcrc (hdr)) {//檢查鏡像頭部的校驗碼(hcrc為0時鏡像頭的校驗碼)
- puts ("Bad Header Checksum/n");
- show_boot_progress (-2);
- return NULL;
- }
- show_boot_progress (3);
- image_print_contents (hdr);//根據傳入的鏡像頭地址,打印鏡像的信息,見下面的分析。
- /*
- Image Name: Linux-2.6.27.8
- Image Type: ARM Linux Kernel Image (uncompressed)
- Data Size: 1828536 Bytes = 1.7 MiB
- Load Address: 80008000
- Entry Point: 80008000
- */
- if (verify) {//是否要對鏡像的數據部分進行校驗
- puts (" Verifying Checksum ... ");
- if (!image_check_dcrc (hdr)) {
- printf ("Bad Data CRC/n");
- show_boot_progress (-3);
- return NULL;
- }
- puts ("OK/n");
- }
- show_boot_progress (4);
- if (!image_check_target_arch (hdr)) {//檢查是否是IH_ARCH_ARM架構
- printf ("Unsupported Architecture 0x%x/n", image_get_arch (hdr));
- show_boot_progress (-4);
- return NULL;
- }
- return hdr;
- }