[轉]u-boot uImage 初探－轉貼部落格

在 u-boot shell 中可以吃的 kernel image 是 uImage, 剛好綱哥他們那一個平台的可以吃 zImage 因為好奇所以稍微 trace 一下.

<Trace>

首先我們來來看一下 u-boot header 那 64 bytes 有啥東西...

@include/image.h

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;

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;
<... 略>
   int verify; /* getenv("verify")[0] != 'n' */
   struct lmb *lmb; /* for memory mgmt */
} bootm_headers_t;

@common/cmd_bootm.c

int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])

在這一個 function 裡其實註解寫的很清楚

/**

* 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
*/

   /* get kernel image header, start address and length */
   os_hdr = boot_get_kernel (cmdtp, flag, argc, argv,
   &images, &os_data, &os_len);

在 boot_get_kernel 中

1 - 會去 parse 由 u-boot shell 中 tftp 0x2000000 uImage 的 0x2000000 轉存成變數 img_addr

2 - 透過 image_get_kernel 中將 header (64 bytes) copy legacy_hdr_os_copy

3 - return img_addr

仔細看一下傳入的 os_data 在這個 boot_get_kernel function 中是會把 64 bytes 的 u-boot header shift 掉的. ( *os_data = image_get_data (hdr) )

接下來

... 略

   case IH_COMP_NONE:
   if (load_start == (ulong)os_hdr) {
   printf (" XIP %s ... ", type_name);
   } else {
   memmove_wd ((void *)load_start,
   (void *)os_data, os_len, CHUNKSZ);

/* 會將 os_data 整個搬到 load_start(0x8000) depends on the architecture */
   }
   load_end = (load_start) + os_len;
   puts("OK\n");
   break;
... 略

整個完成後在呼叫

do_bootm_linux (cmdtp, flag, argc, argv, &images);

上面這一個 function 是一個靜態的.a檔會 based on your architecture 而包進來的 (我的是arm)

所以會在這個 folder 下

@lib_arm/bootm.c

void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
bootm_headers_t *images)
{
... 略

if (images->legacy_hdr_valid) {
ep = image_get_ep (&images->legacy_hdr_os_copy);

/* 將由剛剛搬到的 memory address (0x8000) 指定給 ep */

... 略

theKernel = (void (*)(int, int, uint))ep;

... 略

cleanup_before_linux ();

/* transfer control to the kernel */

theKernel (0, machid, bd->bi_boot_params);
/* does not return */
}

<實作>

那如果我要讓 zImage 也能開機要怎麼做呢？

1. modify common/cmd_bootm.c

將 do_bootm_linux (cmdtp, flag, argc, argv, &images); 加在變數宣告的下面. 只是單純的不讓它去 parse header.

2 . modify lib_arm/bootm.c

do_bootm_linux

... 略

   /* find kernel entry point */
   if (images->legacy_hdr_valid) {
   ep = image_get_ep (&images->legacy_hdr_os_copy)
   printf("ep=%x\n\n", ep);
#if defined(CONFIG_FIT)
   } else if (images->fit_uname_os) {
   ret = fit_image_get_entry (images->fit_hdr_os,
   images->fit_noffset_os, &ep);
   if (ret) {
   puts ("Can't get entry point property!\n");
   goto error;
   }
#endif
   } else {
   ep = CFG_LOAD_ADDR;
   //puts ("Could not find kernel entry point!\n");
   //goto error;
   }