uboot從bootm跳到內核

main_loop中執行的最重要的操作便是引導內核。引導分兩步。第一步先讀取內核鏡像uImage到內存。然後再使用bootm引導內核。

讀取內核只是進行內存復制，因此僅僅需要分析bootm。

1. /*******************************************************************/
2. /* bootm - boot application image from image in memory */
3. /*******************************************************************/
4. 引導應用程序在內存中的鏡像。
5. common/cmd_bootm.c
6. int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
7. {
8. ulong iflag;
9. ulong load_end = 0;
10. int ret;
11. boot_os_fn *boot_fn;
12. /* determine if we have a sub command */檢查是否有子命令
13. if (argc > 1) {
14. char *endp;
15. simple_strtoul(argv[1], &endp, 16); //調用字符串轉無符號整形的函數，endp指向尾字符。
16. /* endp pointing to NULL means that argv[1] was just a
17. * valid number, pass it along to the normal bootm processing 以空字符結尾則當作是合法的數，作為正常引導的參數
18. *
19. * If endp is ':' or '#' assume a FIT identifier so pass
20. * along for normal processing.
21. *
22. * Right now we assume the first arg should never be '-'
23. */
24. if ((*endp != 0) && (*endp != ':') && (*endp != '#')) //是否有子命令。一般不會有，所以這個路徑不會執行。
25. return do_bootm_subcommand(cmdtp, flag, argc, argv);
26. }
27. if (bootm_start(cmdtp, flag, argc, argv)) //bootm_start的分析見下一篇文章。這個函數執行成功返回0，失敗返回1。這個函數主要用於獲取鏡像的信息並存入images。
28. return 1;
29. /*
30. * We have reached the point of no return: we are going to
31. * overwrite all exception vector code, so we cannot easily
32. * recover from any failures any more...
33. */
34. iflag = disable_interrupts();//禁用中斷。
35. ret = bootm_load_os(images.os, &load_end, 1);//將鏡像的數據從images.os.image_start復制到images.os.load 打印：Loading Kernel Image ... OK
36. if (ret < 0) {//上個函數調用失敗才會進入這個路徑
37. if (ret == BOOTM_ERR_RESET)
38. do_reset (cmdtp, flag, argc, argv);
39. if (ret == BOOTM_ERR_OVERLAP) {
40. if (images.legacy_hdr_valid) {
41. if (image_get_type (&images.legacy_hdr_os_copy) == IH_TYPE_MULTI)
42. puts ("WARNING: legacy format multi component "
43. "image overwritten/n");
44. } else {
45. puts ("ERROR: new format image overwritten - "
46. "must RESET the board to recover/n");
47. show_boot_progress (-113);
48. do_reset (cmdtp, flag, argc, argv);
49. }
50. }
51. if (ret == BOOTM_ERR_UNIMPLEMENTED) {
52. if (iflag)
53. enable_interrupts();
54. show_boot_progress (-7);
55. return 1;
56. }
57. }
58. lmb_reserve(&images.lmb, images.os.load, (load_end - images.os.load));//由於沒有定義CONFIG_LMB，這個函數調用被定義為一個空的宏。
59. if (images.os.type == IH_TYPE_STANDALONE) {//處理單獨的程序鏡像。顯然引導內核時不會進入這個路徑。
60. if (iflag)
61. enable_interrupts();
62. /* This may return when 'autostart' is 'no' */
63. bootm_start_standalone(iflag, argc, argv);
64. return 0;
65. }
66. show_boot_progress (8);
67. boot_fn = boot_os[images.os.os];//根據操作系統的類型獲取引導操作系統的函數， boot_os代碼如下。
68. if (boot_fn == NULL) {
69. if (iflag)
70. enable_interrupts();
71. printf ("ERROR: booting os '%s' (%d) is not supported/n",
72. genimg_get_os_name(images.os.os), images.os.os);
73. show_boot_progress (-8);
74. return 1;
75. }
76. arch_preboot_os();//禁用中斷，重設中斷向量
77. boot_fn(0, argc, argv, &images);//調用do_bootm_linux，分析在下面。
78. show_boot_progress (-9);
79. #ifdef DEBUG
80. puts ("/n## Control returned to monitor - resetting.../n");
81. #endif
82. do_reset (cmdtp, flag, argc, argv);
83. return 1;
84. }

2。boot_os

1. static boot_os_fn *boot_os[] = {
2. #ifdef CONFIG_BOOTM_LINUX
3. [IH_OS_LINUX] = do_bootm_linux,
4. #endif
5. #ifdef CONFIG_BOOTM_NETBSD
6. [IH_OS_NETBSD] = do_bootm_netbsd,
7. #endif
8. #ifdef CONFIG_LYNXKDI
9. [IH_OS_LYNXOS] = do_bootm_lynxkdi,
10. #endif
11. #ifdef CONFIG_BOOTM_RTEMS
12. [IH_OS_RTEMS] = do_bootm_rtems,
13. #endif
14. #if defined(CONFIG_CMD_ELF)
15. [IH_OS_VXWORKS] = do_bootm_vxworks,
16. [IH_OS_QNX] = do_bootm_qnxelf,
17. #endif
18. #ifdef CONFIG_INTEGRITY
19. [IH_OS_INTEGRITY] = do_bootm_integrity,
20. #endif
21. };

3。do_bootm_linux
之前所做的引導工作都是與操作系統無關的，接下來都是針對linux 的。
可以看到，參數flag傳過來的是0。

1. arch/arm/lib/bootm.c
2. int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images)
3. {
4. bd_t *bd = gd->bd;
5. char *s;
6. int machid = bd->bi_arch_number;
7. void (*theKernel)(int zero, int arch, uint params);
8. #ifdef CONFIG_CMDLINE_TAG//如果定義了這個宏，將會把bootargs傳給內核。
9. char *commandline = getenv ("bootargs");//獲取bootargs環境變量。
10. #endif
11. if ((flag != 0) && (flag != BOOTM_STATE_OS_GO))
12. return 1;
13. theKernel = (void (*)(int, int, uint))images->ep;//鏡像的入口地址處也就是需要執行的函數入口
14. s = getenv ("machid");
15. if (s) {
16. machid = simple_strtoul (s, NULL, 16);
17. printf ("Using machid 0x%x from environment/n", machid);
18. }
19. show_boot_progress (15);
20. debug ("## Transferring control to Linux (at address %08lx) .../n",
21. (ulong) theKernel);
22. //下面將會初始化傳給內核的標簽（tag），這些標簽裡包含了必要的環境變量和參數。
23. #if defined (CONFIG_SETUP_MEMORY_TAGS) || /
24. defined (CONFIG_CMDLINE_TAG) || /
25. defined (CONFIG_INITRD_TAG) || /
26. defined (CONFIG_SERIAL_TAG) || /
27. defined (CONFIG_REVISION_TAG)
28. setup_start_tag (bd);
29. #ifdef CONFIG_SETUP_MEMORY_TAGS
30. setup_memory_tags (bd);//內存有關的定義
31. #endif
32. #ifdef CONFIG_CMDLINE_TAG
33. setup_commandline_tag (bd, commandline);//將bootargs傳給tag
34. #endif
35. #ifdef CONFIG_INITRD_TAG
36. if (images->rd_start && images->rd_end)//沒有ramdisk所以不會執行這個路徑
37. setup_initrd_tag (bd, images->rd_start, images->rd_end);
38. #endif
39. setup_end_tag (bd);
40. #endif
41. /* we assume that the kernel is in place */
42. printf ("/nStarting kernel .../n/n");//引導內核之前最後一次打印信息。
43. cleanup_before_linux ();//禁用中斷和cache.
44. theKernel (0, machid, bd->bi_boot_params);//跳到內核中執行。<<<<全劇終>>>>
45. /* does not return */
46. return 1;
47. }

4.

1. arch/arm/include/asm
2. /* The list must start with an ATAG_CORE node */
3. #define ATAG_CORE 0x54410001
4. struct tag_core {
5. u32 flags; /* bit 0 = read-only */
6. u32 pagesize;
7. u32 rootdev;
8. };
9. /* command line: /0 terminated string */
10. #define ATAG_CMDLINE 0x54410009
11. struct tag_cmdline {//bootargs保存在它的後面
12. char cmdline[1]; /* this is the minimum size */
13. };
14. /* describes where the compressed ramdisk image lives (virtual address) */
15. /*
16. * this one accidentally used virtual addresses - as such,
17. * its depreciated.
18. */
19. #define ATAG_INITRD 0x54410005
20. /* describes where the compressed ramdisk image lives (physical address) */
21. #define ATAG_INITRD2 0x54420005
22. struct tag_initrd {//描述ramdisk的分布
23. u32 start; /* physical start address */
24. u32 size; /* size of compressed ramdisk image in bytes */
25. };
26. /* it is allowed to have multiple ATAG_MEM nodes */
27. #define ATAG_MEM 0x54410002
28. struct tag_mem32 {
29. u32 size;
30. u32 start; /* physical start address */
31. };
32. struct tag_header {
33. u32 size;
34. u32 tag;
35. };
36. struct tag {
37. struct tag_header hdr;
38. union {
39. struct tag_core core;
40. struct tag_mem32 mem;
41. struct tag_videotext videotext;
42. struct tag_ramdisk ramdisk;
43. struct tag_initrd initrd;
44. struct tag_serialnr serialnr;
45. struct tag_revision revision;
46. struct tag_videolfb videolfb;
47. struct tag_cmdline cmdline;
48. /*
49. * Acorn specific
50. */
51. struct tag_acorn acorn;
52. /*
53. * DC21285 specific
54. */
55. struct tag_memclk memclk;
56. } u;
57. };

5

1. arch/arm/include/asm/setup.h
2. #define tag_next(t) ((struct tag *)((u32 *)(t) + (t)->hdr.size))//跳到下一個tag地址處
3. arch/arm/lib/bootm.c
4. static void setup_start_tag (bd_t *bd)
5. {
6. params = (struct tag *) bd->bi_boot_params; //CFG_ENV_ADDR(0x80000100)設置環境變量的頭地址。
7. params->hdr.tag = ATAG_CORE; //第一個tag默認為 tag_core。ATAG_CORE 是默認的開始類型。
8. params->hdr.size = tag_size (tag_core);
9. params->u.core.flags = 0;
10. params->u.core.pagesize = 0;
11. params->u.core.rootdev = 0;
12. params = tag_next (params); //跳到下一個tag地址處
13. }
14. #ifdef CONFIG_SETUP_MEMORY_TAGS
15. static void setup_memory_tags (bd_t *bd)//設置內存分布的tag
16. {
17. int i;
18. for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {//如果有多個內存芯片，則會循環多次。對3250來說，只有一片。
19. params->hdr.tag = ATAG_MEM;
20. params->hdr.size = tag_size (tag_mem32);
21. params->u.mem.start = bd->bi_dram[i].start;//內存塊的開始地址。PHYS_SDRAM_1;在smartarm3250.h中,起始地址(0x80000000)
22. params->u.mem.size = bd->bi_dram[i].size;//內存塊的大小
23. params = tag_next (params);//跳到下一個tag地址處
24. }
25. }
26. #endif /* CONFIG_SETUP_MEMORY_TAGS */
27. static void setup_commandline_tag (bd_t *bd, char *commandline)
28. {
29. char *p;
30. if (!commandline)
31. return;
32. /* eat leading white space */
33. for (p = commandline; *p == ' '; p++);//跳過開頭的空格
34. /* skip non-existent command lines so the kernel will still
35. * use its default command line.
36. */
37. if (*p == '/0')
38. return;
39. params->hdr.tag = ATAG_CMDLINE;
40. params->hdr.size =
41. (sizeof (struct tag_header) + strlen (p) + 1 + 4) >> 2;
42. strcpy (params->u.cmdline.cmdline, p);//將bootargs復制到cmdline後面。
43. params = tag_next (params);//跳到下一個tag地址處
44. }
45. #ifdef CONFIG_INITRD_TAG
46. static void setup_initrd_tag (bd_t *bd, ulong initrd_start, ulong initrd_end)
47. {
48. /* an ATAG_INITRD node tells the kernel where the compressed
49. * ramdisk can be found. ATAG_RDIMG is a better name, actually.
50. */
51. params->hdr.tag = ATAG_INITRD2;
52. params->hdr.size = tag_size (tag_initrd);
53. params->u.initrd.start = initrd_start;
54. params->u.initrd.size = initrd_end - initrd_start;
55. params = tag_next (params);
56. }
57. #endif /* CONFIG_INITRD_TAG */
58. static void setup_end_tag (bd_t *bd)
59. {
60. params->hdr.tag = ATAG_NONE;//最後一個tag是一個空類型，標志這tag的結束。
61. params->hdr.size = 0;
62. }