uboot分析之bootm_start

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

1. static int bootm_start(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
2. {
3. void *os_hdr;
4. int ret;
5. 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。
6. 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。
7. bootm_start_lmb();//不做任何有意義的工作，除了定義# define lmb_reserve(lmb, base, size)
8. /* 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。
9. os_hdr = boot_get_kernel (cmdtp, flag, argc, argv,
10. &images, &images.os.image_start, &images.os.image_len);//返回指向內存中鏡像頭的指針
11. if (images.os.image_len == 0) {
12. puts ("ERROR: can't get kernel image!/n");
13. return 1;
14. }
15. /* get image parameters */
16. switch (genimg_get_format (os_hdr)) {//根據鏡像魔數獲取鏡像類型
17. case IMAGE_FORMAT_LEGACY:
18. images.os.type = image_get_type (os_hdr);//鏡像類型
19. images.os.comp = image_get_comp (os_hdr);//壓縮類型
20. images.os.os = image_get_os (os_hdr);//操作系統類型
21. images.os.end = image_get_image_end (os_hdr);//當前鏡像的尾地址
22. images.os.load = image_get_load (os_hdr);//鏡像數據的載入地址
23. break;
24. default:
25. puts ("ERROR: unknown image format type!/n");
26. return 1;
27. }
28. /* find kernel entry point */
29. if (images.legacy_hdr_valid) {//如果鏡像已經通過驗證
30. images.ep = image_get_ep (&images.legacy_hdr_os_copy);//獲取入口地址，填充images.ep 。
31. } else {
32. puts ("Could not find kernel entry point!/n");
33. return 1;
34. }
35. if (((images.os.type == IH_TYPE_KERNEL) ||
36. (images.os.type == IH_TYPE_MULTI)) &&
37. (images.os.os == IH_OS_LINUX)) {
38. /* find ramdisk */3250的配置中這個函數不做任何工作
39. ret = boot_get_ramdisk (argc, argv, &images, IH_INITRD_ARCH,
40. &images.rd_start, &images.rd_end);
41. if (ret) {
42. puts ("Ramdisk image is corrupt or invalid/n");
43. return 1;
44. }
45. }
46. images.os.start = (ulong)os_hdr;//指向內存中鏡像的頭地址
47. images.state = BOOTM_STATE_START;//標記引導狀態
48. return 0;
49. }

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

1. typedef struct bootm_headers {
2. /*
3. * Legacy os image header, if it is a multi component image
4. * then boot_get_ramdisk() and get_fdt() will attempt to get
5. * data from second and third component accordingly.
6. */
7. image_header_t *legacy_hdr_os; /* image header pointer */
8. image_header_t legacy_hdr_os_copy; /* header copy */
9. ulong legacy_hdr_valid;
10. #ifndef USE_HOSTCC
11. image_info_t os; /* os image info */
12. ulong ep; /* entry point of OS */
13. ulong rd_start, rd_end;/* ramdisk start/end */
14. ulong ft_len; /* length of flat device tree */
15. ulong initrd_start;
16. ulong initrd_end;
17. ulong cmdline_start;
18. ulong cmdline_end;
19. bd_t *kbd;
20. #endif
21. int verify; /* getenv("verify")[0] != 'n' */
22. #define BOOTM_STATE_START (0x00000001)
23. #define BOOTM_STATE_LOADOS (0x00000002)
24. #define BOOTM_STATE_RAMDISK (0x00000004)
25. #define BOOTM_STATE_FDT (0x00000008)
26. #define BOOTM_STATE_OS_CMDLINE (0x00000010)
27. #define BOOTM_STATE_OS_BD_T (0x00000020)
28. #define BOOTM_STATE_OS_PREP (0x00000040)
29. #define BOOTM_STATE_OS_GO (0x00000080)
30. int state;
31. } bootm_headers_t;
32. /*
33. * Legacy format image header,
34. * all data in network byte order (aka natural aka bigendian).
35. */內核鏡像頭 include/image.h
36. typedef struct image_header {
37. uint32_t ih_magic; /* Image Header Magic Number */鏡像頭部幻數，為#define IH_MAGIC 0x27051956
38. uint32_t ih_hcrc; /* Image Header CRC Checksum */鏡像頭部crc校驗碼
39. uint32_t ih_time; /* Image Creation Timestamp */鏡像創建時間戳
40. uint32_t ih_size; /* Image Data Size */鏡像數據大小（不算頭部）1828536
41. uint32_t ih_load; /* Data Load Address */數據將要載入的內存地址 80008000
42. uint32_t ih_ep; /* Entry Point Address */鏡像入口地址 80008000
43. uint32_t ih_dcrc; /* Image Data CRC Checksum */鏡像數據校驗碼
44. uint8_t ih_os; /* Operating System */操作系統類型 #define IH_OS_LINUX 5
45. uint8_t ih_arch; /* CPU architecture */CPU架構類型 #define IH_ARCH_ARM 2
46. uint8_t ih_type; /* Image Type */鏡像類型 IH_TYPE_KERNEL
47. uint8_t ih_comp; /* Compression Type */壓縮類型 IH_COMP_NONE
48. uint8_t ih_name[IH_NMLEN]; /* Image Name */鏡像名字Linux-2.6.27.8，#define IH_NMLEN 32
49. } image_header_t;
50. 鏡像信息 include/image.h
51. typedef struct image_info {
52. ulong start, end; /* start/end of blob */鏡像的起始地址和尾地址
53. 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
54. ulong load; /* load addr for the image */鏡像數據的裝載地址
55. 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
56. } image_info_t;

3。boot_get_kernel

1. /**
2. * boot_get_kernel - find kernel image
3. * @os_data: pointer to a ulong variable, will hold os data start address
4. * @os_len: pointer to a ulong variable, will hold os data length
5. *
6. * boot_get_kernel() tries to find a kernel image, verifies its integrity
7. * and locates kernel data.
8. *
9. * returns:
10. * pointer to image header if valid image was found, plus kernel start
11. * address and length, otherwise NULL
12. */
13. 尋找可用的內核鏡像
14. static void *boot_get_kernel (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
15. bootm_headers_t *images, ulong *os_data, ulong *os_len)
16. {
17. image_header_t *hdr;
18. ulong img_addr;
19. /* find out kernel image address */
20. if (argc < 2) {//如果參數太少
21. 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;
22. debug ("* kernel: default image load address = 0x%08lx/n",
23. load_addr);
24. } else {
25. 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
26. debug ("* kernel: cmdline image address = 0x%08lx/n", img_addr);
27. }
28. show_boot_progress (1);
29. /* copy from dataflash if needed */
30. img_addr = genimg_get_image (img_addr);//對於3250，這個函數什麼都沒做。因為沒有dataflash.
31. /* check image type, for FIT images get FIT kernel node */
32. *os_data = *os_len = 0;
33. 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。
34. case IMAGE_FORMAT_LEGACY:
35. printf ("## Booting kernel from Legacy Image at %08lx .../n", //打印引導消息
36. img_addr);
37. 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。
38. if (!hdr)
39. return NULL;
40. show_boot_progress (5);
41. /* get os_data and os_len */
42. switch (image_get_type (hdr)) {
43. case IH_TYPE_KERNEL:
44. *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。
45. *os_len = image_get_data_size (hdr);//鏡像數據部分大小
46. break;
47. case IH_TYPE_MULTI:
48. image_multi_getimg (hdr, 0, os_data, os_len);
49. break;
50. case IH_TYPE_STANDALONE:
51. *os_data = image_get_data (hdr);
52. *os_len = image_get_data_size (hdr);
53. break;
54. default:
55. printf ("Wrong Image Type for %s command/n", cmdtp->name);
56. show_boot_progress (-5);
57. return NULL;
58. }
59. /*
60. * copy image header to allow for image overwrites during kernel
61. * decompression.
62. */拷貝一份鏡像的頭部到images中。
63. memmove (&images->legacy_hdr_os_copy, hdr, sizeof(image_header_t));
64. /* save pointer to image header */
65. images->legacy_hdr_os = hdr;//images中指針指向鏡像的頭部
66. images->legacy_hdr_valid = 1;//鏡像已經檢驗合格，置標志量
67. show_boot_progress (6);
68. break;
69. default:
70. printf ("Wrong Image Format for %s command/n", cmdtp->name);
71. show_boot_progress (-108);
72. return NULL;
73. }
74. debug (" kernel data at 0x%08lx, len = 0x%08lx (%ld)/n",
75. *os_data, *os_len, *os_len);
76. return (void *)img_addr;
77. }

4。image_get_kernel

1. common/cmd_bootm.c
2. static image_header_t *image_get_kernel (ulong img_addr, int verify)
3. {
4. image_header_t *hdr = (image_header_t *)img_addr;
5. if (!image_check_magic(hdr)) { //檢查鏡像頭部的魔數是否等於 IH_MAGIC
6. puts ("Bad Magic Number/n");
7. show_boot_progress (-1);
8. return NULL;
9. }
10. show_boot_progress (2);
11. 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）
12. puts ("Bad Header Checksum/n");
13. show_boot_progress (-2);
14. return NULL;
15. }
16. show_boot_progress (3);
17. 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。
18. /*
19. Image Name: Linux-2.6.27.8
20. Image Type: ARM Linux Kernel Image (uncompressed)
21. Data Size: 1828536 Bytes = 1.7 MiB
22. Load Address: 80008000
23. Entry Point: 80008000
24. */
25. if (verify) {//是否要對鏡像的數據部分進行校驗
26. puts (" Verifying Checksum ... ");
27. if (!image_check_dcrc (hdr)) {
28. printf ("Bad Data CRC/n");
29. show_boot_progress (-3);
30. return NULL;
31. }
32. puts ("OK/n");
33. }
34. show_boot_progress (4);
35. if (!image_check_target_arch (hdr)) {//檢查是否是IH_ARCH_ARM架構
36. printf ("Unsupported Architecture 0x%x/n", image_get_arch (hdr));
37. show_boot_progress (-4);
38. return NULL;
39. }
40. return hdr;
41. }