int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
{
ulong iflag;
ulong addr;
ulong data, len, checksum;
ulong *len_ptr;
uint unc_len = CFG_BOOTM_LEN;
int i, verify;
char *name, *s;
int (*appl)(int, char *[]);
image_header_t *hdr = &header;
/*为是否对镜像头做校验做准备,读取uboot的环境变量verify,
如果环境变量verify等于’n’,则局部变量verify赋值成为0;如果环境变量verify为空(即没有
定义环境变量verify)或者环境变量verify不等于’n’,则局部变量verify赋值成为1
*/
s = getenv ("verify");
verify = (s && (*s == 'n')) ? 0 : 1;
if (argc < 2) //获取镜像存放的内存首地址,如果参数个数小于2(即只是输入了bootm),使用缺省加载地址CFG_LOAD_ADDR。
{
addr = load_addr;
}
else //否则使用第二个参数作为加载地址
{
addr = simple_strtoul(argv[1], NULL, 16);
}
SHOW_BOOT_PROGRESS (1);
printf ("## Booting image at %08lx ...\n", addr);
/* Copy header so we can blank CRC field for re-calculation */
#ifdef CONFIG_HAS_DATAFLASH
if (addr_dataflash(addr)){
read_dataflash(addr, sizeof(image_header_t), (char *)&header);
} else
#endif
//从镜像内存首地址读取镜像头部,为下面的分析校验做准备
memmove (&header, (char *)addr, sizeof(image_header_t));
//判断内核头部编号属性是否为IH_MAGIC,如果不是u-boot镜像识别的内核镜像格式,会输出提示信息”Bad Magic Number”
if (ntohl(hdr->ih_magic) != IH_MAGIC)
{
#ifdef __I386__ /* correct image format not implemented yet - fake it */
if (fake_header(hdr, (void*)addr, -1) != NULL)
{
/* to compensate for the addition below */
addr -= sizeof(image_header_t);
/* turnof verify,
* fake_header() does not fake the data crc
*/
verify = 0;
}
else
#endif /* __I386__ */
{
puts ("Bad Magic Number\n");
SHOW_BOOT_PROGRESS (-1);
return 1;
}
}
SHOW_BOOT_PROGRESS (2);
data = (ulong)&header;
len = sizeof(image_header_t);
//对内核的镜像头部做CRC检验
checksum = ntohl(hdr->ih_hcrc);
hdr->ih_hcrc = 0;
if (crc32 (0, (uchar *)data, len) != checksum)
{
puts ("Bad Header Checksum\n");
SHOW_BOOT_PROGRESS (-2);
return 1;
}
SHOW_BOOT_PROGRESS (3);
#ifdef CONFIG_HAS_DATAFLASH
if (addr_dataflash(addr))
{
len = ntohl(hdr->ih_size) + sizeof(image_header_t);
read_dataflash(addr, len, (char *)CFG_LOAD_ADDR);
addr = CFG_LOAD_ADDR;
}
#endif
/* for multi-file images we need the data part, too */
print_image_hdr ((image_header_t *)addr);
data = addr + sizeof(image_header_t);
len = ntohl(hdr->ih_size);
if (verify) //对镜像头部的数据做CRC校验
{
puts (" Verifying Checksum ... ");
if (crc32 (0, (uchar *)data, len) != ntohl(hdr->ih_dcrc)) {
printf ("Bad Data CRC\n");
SHOW_BOOT_PROGRESS (-3);
return 1;
}
puts ("OK\n");
}
SHOW_BOOT_PROGRESS (4);
len_ptr = (ulong *)data;
//检验CPU的类型
#if defined(__PPC__)
if (hdr->ih_arch != IH_CPU_PPC)
#elif defined(__ARM__)
if (hdr->ih_arch != IH_CPU_ARM)
#elif defined(__I386__)
if (hdr->ih_arch != IH_CPU_I386)
#elif defined(__mips__)
if (hdr->ih_arch != IH_CPU_MIPS)
#elif defined(__nios__)
if (hdr->ih_arch != IH_CPU_NIOS)
#elif defined(__M68K__)
if (hdr->ih_arch != IH_CPU_M68K)
#elif defined(__microblaze__)
if (hdr->ih_arch != IH_CPU_MICROBLAZE)
#elif defined(__nios2__)
if (hdr->ih_arch != IH_CPU_NIOS2)
#elif defined(__blackfin__)
if (hdr->ih_arch != IH_CPU_BLACKFIN)
#elif defined(__avr32__)
if (hdr->ih_arch != IH_CPU_AVR32)
#else
# error Unknown CPU type
#endif
{
printf ("Unsupported Architecture 0x%x\n", hdr->ih_arch);
SHOW_BOOT_PROGRESS (-4);
return 1;
}
SHOW_BOOT_PROGRESS (5);
switch (hdr->ih_type) {
case IH_TYPE_STANDALONE:
name = "Standalone Application";
/* A second argument overwrites the load address */
if (argc > 2) {
hdr->ih_load = htonl(simple_strtoul(argv[2], NULL, 16));
}
break;
case IH_TYPE_KERNEL:
name = "Kernel Image";
break;
case IH_TYPE_MULTI:
name = "Multi-File Image";
len = ntohl(len_ptr[0]);
/* OS kernel is always the first image */
data += 8; /* kernel_len + terminator */
for (i=1; len_ptr[i]; ++i)
data += 4;
break;
default: printf ("Wrong Image Type for %s command\n", cmdtp->name);
SHOW_BOOT_PROGRESS (-5);
return 1;
}
SHOW_BOOT_PROGRESS (6);
/*
* We have reached the point of no return: we are going to
* overwrite all exception vector code, so we cannot easily
* recover from any failures any more...
*/
iflag = disable_interrupts();
#ifdef CONFIG_AMIGAONEG3SE
/*
* We've possible left the caches enabled during
* bios emulation, so turn them off again
*/
icache_disable();
invalidate_l1_instruction_cache();
flush_data_cache();
dcache_disable();
#endif
switch (hdr->ih_comp) //开始判断是否对内核进行了压缩
{
//首先清楚这几个地址的定义addr = CFG_LOAD_ADDR; data = addr + sizeof(image_header_t);
case IH_COMP_NONE: //如果没有被压缩,只是在内核的前面加了一个头部信息
//在利用mkimage时指定-a选项后面就是指定的内核加载的地址,这个地址会被存放到镜像头结构的ih_load成员变量中,如在smdk2410中ih_load为0x30008000
//如果加载地址等于addr(即:bootm后面接的地址)就不移动内核,可以在这个addr上开始加载,此时的内核入口地址就是addr后的64字节,即data
if(ntohl(hdr->ih_load) == addr)
{
printf (" XIP %s ... ", name);
}
/*
ih_load不等于addr,此时:data=addr+64还是指向真正的内核部分,这时候就要将内核拷贝到ih_load指定的地方才能执行,这种情况ih_load==ih_ep加载地址等于内核的入口地址
*/
else
{
#if defined(CONFIG_HW_WATCHDOG) || defined(CONFIG_WATCHDOG)
size_t l = len;
void *to = (void *)ntohl(hdr->ih_load);
void *from = (void *)data;
printf (" Loading %s ... ", name);
while (l > 0) {
size_t tail = (l > CHUNKSZ) ? CHUNKSZ : l;
WATCHDOG_RESET();
memmove (to, from, tail);
to += tail;
from += tail;
l -= tail;
}
#else /* !(CONFIG_HW_WATCHDOG || CONFIG_WATCHDOG) */
memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
//内核移动函数:将data地址处的真正内核复制到指定的ih_load处
#endif /* CONFIG_HW_WATCHDOG || CONFIG_WATCHDOG */
}
break;
case IH_COMP_GZIP: //内核文件有压缩成gzip格式情况:需要解压缩
printf (" Uncompressing %s ... ", name);
if (gunzip ((void *)ntohl(hdr->ih_load), unc_len,(uchar *)data, &len) != 0)
{
puts ("GUNZIP ERROR - must RESET board to recover\n");
SHOW_BOOT_PROGRESS (-6);
do_reset (cmdtp, flag, argc, argv);
}
break;
#ifdef CONFIG_BZIP2//内核文件有压缩成bzip2格式情况:需要解压缩
case IH_COMP_BZIP2:
printf (" Uncompressing %s ... ", name);
/*
* If we've got less than 4 MB of malloc() space,
* use slower decompression algorithm which requires
* at most 2300 KB of memory.
*/
i = BZ2_bzBuffToBuffDecompress ((char*)ntohl(hdr->ih_load),
&unc_len, (char *)data, len,
CFG_MALLOC_LEN < (4096 * 1024), 0);
if (i != BZ_OK) {
printf ("BUNZIP2 ERROR %d - must RESET board to recover\n", i);
SHOW_BOOT_PROGRESS (-6);
udelay(100000);
do_reset (cmdtp, flag, argc, argv);
}
break;
#endif /* CONFIG_BZIP2 */
default:
if (iflag)
enable_interrupts();
printf ("Unimplemented compression type %d\n", hdr->ih_comp);
SHOW_BOOT_PROGRESS (-7);
return 1;
}
puts ("OK\n");
SHOW_BOOT_PROGRESS (7);
switch (hdr->ih_type) {
case IH_TYPE_STANDALONE:
if (iflag)
enable_interrupts();
/* load (and uncompress), but don't start if "autostart"
* is set to "no"
*/
if (((s = getenv("autostart")) != NULL) && (strcmp(s,"no") == 0)) {
char buf[32];
sprintf(buf, "%lX", len);
setenv("filesize", buf);
return 0;
}
appl = (int (*)(int, char *[]))ntohl(hdr->ih_ep);
(*appl)(argc-1, &argv[1]);
return 0;
case IH_TYPE_KERNEL:
case IH_TYPE_MULTI:
/* handled below */
break;
default:
if (iflag)
enable_interrupts();
printf ("Can't boot image type %d\n", hdr->ih_type);
SHOW_BOOT_PROGRESS (-8);
return 1;
}
SHOW_BOOT_PROGRESS (8);
switch (hdr->ih_os) //确定内核的操作系统
{
default: /* handled by (original) Linux case */
case IH_OS_LINUX: //选定为Linux操作系统
#ifdef CONFIG_SILENT_CONSOLE
fixup_silent_linux();
#endif
//调用do_bootm_linux函数启动内核,接着分析armlinux.c文件下的这个函数,从这里传入的参数有:
do_bootm_linux (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
case IH_OS_NETBSD:
do_bootm_netbsd (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#ifdef CONFIG_LYNXKDI
case IH_OS_LYNXOS:
do_bootm_lynxkdi (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#endif
case IH_OS_RTEMS:
do_bootm_rtems (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#if (CONFIG_COMMANDS & CFG_CMD_ELF)
case IH_OS_VXWORKS:
do_bootm_vxworks (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
case IH_OS_QNX:
do_bootm_qnxelf (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#endif /* CFG_CMD_ELF */
#ifdef CONFIG_ARTOS
case IH_OS_ARTOS:
do_bootm_artos (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#endif
}
SHOW_BOOT_PROGRESS (-9);
#ifdef DEBUG
puts ("\n## Control returned to monitor - resetting...\n");
do_reset (cmdtp, flag, argc, argv);
#endif
return 1;
}