uboot之bootm命令分析
2012-07-23 23:11
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/*本文的部分内容参考了http://blog.csdn.net/xitijie/article/details/7004737这篇文章，在此表示感谢*/
bootm要做的事情：
1. 读取头部，把内核拷贝到合适的地方
2. 把参数给内核准备好，并告诉内核参数的首地址
3. 引导内核
启动内核：
do_bootm_linux: 1. 设置参数，跳到入口地址theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
参数的传递：在某个地址按某种格式，存放好数据
uboot引导linux内核之do_bootm解析：
do_bootm
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;
s = getenv ("verify"); //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。
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；否则使用第二个参数作为加载地址。
addr = load_addr;
} else {
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
memmove (&header, (char *)addr, sizeof(image_header_t));//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
if (ntohl(hdr->ih_magic) != IH_MAGIC) { //判断文件头中的幻数是否为IH_MAGIC，所以如果不是u-boot镜像格式，会输出提示信息”Bad Magic Number”
#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);
checksum = ntohl(hdr->ih_hcrc); //对镜像头做crc校验
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) { //对镜像的数据部分做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;
#if defined(__PPC__) //校验cpu类型是否正确
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) { //根据镜像的压缩类型把内核镜像解压到指定的地址，一般是mkimage时-a指定的
那个地址，-a指定的那个地址也就是存储在镜像头里面的hdr->ih_load变量中，
什么时候指定的呢，其实就是在执行mkimage指令的时候，-a输入的时候，赋给的数值
case IH_COMP_NONE:
if(ntohl(hdr->ih_load) == addr) { //如果image header中指示的加载地址和bootm命令中参数2指定的地址相同，则表示不需要copy，可以就地执行。
printf (" XIP %s ... ", name);
} 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) */如果image header中指示的加载地址和bootm命令中参数2指定的地址不相同，则表示要从image header中指示的加载地址处把image data copy到bootm命令中参数2指定的地址处，然后再执行。
memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
#endif /* CONFIG_HW_WATCHDOG || CONFIG_WATCHDOG */
}
break;
case IH_COMP_GZIP:
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
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) {
default:
/* handled by (original) Linux case */
case IH_OS_LINUX:
#ifdef CONFIG_SILENT_CONSOLE
fixup_silent_linux();
#endif //这个函数接下来做进一步的跳转前的准备工作，在这之前，就是各种校验和数据解压拷贝工作。
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;
}
先来引用一下这篇介绍“ARM Linux内核启动要求”的文章ARM Linux Kernel Boot Requirements，是ARM Linux内核的维护者Russell King写的。
引用：
* CPU register settings
o r0 = 0.
o r1 = machine type number.
o r2 = physical address of tagged list in system RAM.
* CPU mode
o All forms of interrupts must be disabled (IRQs and FIQs.)
o The CPU must be in SVC mode. (A special exception exists for Angel.)
* Caches, MMUs
o The MMU must be off.
o Instruction cache may be on or off.
o Data cache must be off and must not contain any stale data.
* Devices
o DMA to/from devices should be quiesced.
* The boot loader is expected to call the kernel image by jumping directly to the first instruction of the kernel image.
下面对do_bootm_linux函数做一下注释，便于大家理解boot的过程。
void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
ulong addr, ulong *len_ptr, int verify)
{
ulong len = 0, checksum;
ulong initrd_start, initrd_end;
ulong data;
void (*theKernel)(int zero, int arch, uint params);
image_header_t *hdr = &header;
bd_t *bd = gd->bd;
#ifdef CONFIG_CMDLINE_TAG
char *commandline = getenv ("bootargs");
#endif
//可以看到theKernel被赋值为hdr->ih_ep，这个hdr是指使用tools/mkimage工具程
//序制作uImage时加在linux.bin.gz前面的一个头部，而ih_ep结构体成员保存的就是使用mkimage时指定
//的-e参数的值，即内核的入口点（Entry Point）。知道了hdr->ih_ep的意义之后，给theKernel赋这个
//值也就是理所当然的了。
theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
/*
* Check if there is an initrd image
*/
if (argc >= 3) {
SHOW_BOOT_PROGRESS (9);
addr = simple_strtoul (argv[2], NULL, 16);
printf ("## Loading Ramdisk 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
memcpy (&header, (char *) addr,
sizeof (image_header_t));
if (ntohl (hdr->ih_magic) != IH_MAGIC) {
printf ("Bad Magic Number\n");
SHOW_BOOT_PROGRESS (-10);
do_reset (cmdtp, flag, argc, argv);
}
data = (ulong) & header;
len = sizeof (image_header_t);
checksum = ntohl (hdr->ih_hcrc);
hdr->ih_hcrc = 0;
if (crc32 (0, (unsigned char *) data, len) != checksum) {
printf ("Bad Header Checksum\n");
SHOW_BOOT_PROGRESS (-11);
do_reset (cmdtp, flag, argc, argv);
}
SHOW_BOOT_PROGRESS (10);
print_image_hdr (hdr);
data = addr + sizeof (image_header_t);
len = ntohl (hdr->ih_size);
#ifdef CONFIG_HAS_DATAFLASH
if (addr_dataflash (addr)) {
read_dataflash (data, len, (char *) CFG_LOAD_ADDR);
data = CFG_LOAD_ADDR;
}
#endif
if (verify) {
ulong csum = 0;
printf (" Verifying Checksum ... ");
csum = crc32 (0, (unsigned char *) data, len);
if (csum != ntohl (hdr->ih_dcrc)) {
printf ("Bad Data CRC\n");
SHOW_BOOT_PROGRESS (-12);
do_reset (cmdtp, flag, argc, argv);
}
printf ("OK\n");
}
SHOW_BOOT_PROGRESS (11);
if ((hdr->ih_os != IH_OS_LINUX) ||
(hdr->ih_arch != IH_CPU_ARM) ||
(hdr->ih_type != IH_TYPE_RAMDISK)) {
printf ("No Linux ARM Ramdisk Image\n");
SHOW_BOOT_PROGRESS (-13);
do_reset (cmdtp, flag, argc, argv);
}
#if defined(CONFIG_B2) || defined(CONFIG_EVB4510) || defined(CONFIG_ARMADILLO)
/*
*we need to copy the ramdisk to SRAM to let Linux boot
*/
memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
data = ntohl(hdr->ih_load);
#endif /* CONFIG_B2 || CONFIG_EVB4510 */
/*
* Now check if we have a multifile image
*/
} else if ((hdr->ih_type == IH_TYPE_MULTI) && (len_ptr[1])) {
ulong tail = ntohl (len_ptr[0]) % 4;
int i;
SHOW_BOOT_PROGRESS (13);
/* skip kernel length and terminator */
data = (ulong) (&len_ptr[2]);
/* skip any additional image length fields */
for (i = 1; len_ptr[i]; ++i)
data += 4;
/* add kernel length, and align */
data += ntohl (len_ptr[0]);
if (tail) {
data += 4 - tail;
}
len = ntohl (len_ptr[1]);
} else {
/*
* no initrd image
*/
SHOW_BOOT_PROGRESS (14);
len = data = 0;
}
#ifdef DEBUG
if (!data) {
printf ("No initrd\n");
}
#endif
if (data) {
initrd_start = data;
initrd_end = initrd_start + len;
} else {
initrd_start = 0;
initrd_end = 0;
}
SHOW_BOOT_PROGRESS (15);
debug ("## Transferring control to Linux (at address %08lx) ...\n",
(ulong) theKernel);
#if defined (CONFIG_SETUP_MEMORY_TAGS) || \
defined (CONFIG_CMDLINE_TAG) || \
defined (CONFIG_INITRD_TAG) || \
defined (CONFIG_SERIAL_TAG) || \
defined (CONFIG_REVISION_TAG) || \
defined (CONFIG_LCD) || \
defined (CONFIG_VFD)
setup_start_tag (bd);
#ifdef CONFIG_SERIAL_TAG
setup_serial_tag (¶ms);
#endif
#ifdef CONFIG_REVISION_TAG
setup_revision_tag (¶ms);
#endif
#ifdef CONFIG_SETUP_MEMORY_TAGS
setup_memory_tags (bd);
#endif
#ifdef CONFIG_CMDLINE_TAG
setup_commandline_tag (bd, commandline);
#endif
#ifdef CONFIG_INITRD_TAG
if (initrd_start && initrd_end)
setup_initrd_tag (bd, initrd_start, initrd_end);
#endif
#if defined (CONFIG_VFD) || defined (CONFIG_LCD)
setup_videolfb_tag ((gd_t *) gd);
#endif
setup_end_tag (bd);
#endif
/* we assume that the kernel is in place */
printf ("\nStarting kernel ...\n\n");
#ifdef CONFIG_USB_DEVICE
{
extern void udc_disconnect (void);
//udc_disconnect (); // cancled by www.embedsky.net
}
#endif
cleanup_before_linux ();
//看看它的名字和参数的命名我们也可以猜到这个其实就是内核的入口函
//数的指针了。几个参数的命名也说明了上文提到的ARM Linux内核启动要求的第一条，
//因为根据ACPS（ARM/Thumb Procedure Call Standard）的规定，这三个参数就是依次
//使用r0，r1和r2来传递的。
调用的时候对参数进行赋值，r0=0，r1=bd->bi_arch_number，r2=bd->bi_boot_params，
一个都不少。至此U-Boot的使命完成，linux开始统治整个世界。
theKernel (0, bd->bi_arch_number, bd->bi_boot_params);
}
bootm命令是用来引导经过u-boot的工具mkimage打包后的kernel image的，什么叫做经
过u-boot的工具mkimage打包后的kernel image，这个就要看mkimage的用法:
mkimage的用法
uboot源代码的tools/目录下有mkimage工具，这个工具可以用来制作不压缩或者压缩的多种可启动映象文件。
mkimage在制作映象文件的时候，是在原来的可执行映象文件的前面加上一个0x40字节的头，记录参数所指定的信息，这样uboot才能识别这个映象是针对哪个CPU体系结构的，哪个OS的，哪种类型，加载内存中的哪个位置， 入口点在内存的那个位置以及映象名是什么
引用：
root@Glym:/tftpboot# ./mkimage
Usage: ./mkimage -l image
-l ==> list image header information
./mkimage -A arch -O os -T type -C comp -a addr -e ep -n name -d data_file[:data_file...] image
-A ==> set architecture to 'arch'
-O ==> set operating system to 'os'
-T ==> set image type to 'type'
-C ==> set compression type 'comp'
-a ==> set load address to 'addr' (hex)
-e ==> set entry point to 'ep' (hex)
-n ==> set image name to 'name'
-d ==> use image data from 'datafile'
-x ==> set XIP (execute in place)
参数说明：
-A 指定CPU的体系结构：
取值 表示的体系结构
alpha Alpha
arm A RM
x86 Intel x86
ia64 IA64
mips MIPS
mips64 MIPS 64 Bit
ppc PowerPC
s390 IBM S390
sh SuperH
sparc SPARC
sparc64 SPARC 64 Bit
m68k MC68000
-O 指定操作系统类型，可以取以下值：
openbsd、netbsd、freebsd、4_4bsd、linux、svr4、esix、solaris、irix、sco、dell、ncr、lynxos、vxworks、psos、qnx、u-boot、rtems、artos
-T 指定映象类型，可以取以下值：
standalone、kernel、ramdisk、multi、firmware、script、filesystem
-C 指定映象压缩方式，可以取以下值：
none 不压缩
gzip 用gzip的压缩方式
bzip2 用bzip2的压缩方式
-a 指定映象在内存中的加载地址，映象下载到内存中时，要按照用mkimage制作映象时，这个参数所指定的地址值来下载
-e 指定映象运行的入口点地址，这个地址就是-a参数指定的值加上0x40（因为前面有个mkimage添加的0x40个字节的头）
-n 指定映象名
-d 指定制作映象的源文件
bootm要做的事情：
1. 读取头部，把内核拷贝到合适的地方
2. 把参数给内核准备好，并告诉内核参数的首地址
3. 引导内核
启动内核：
do_bootm_linux: 1. 设置参数，跳到入口地址theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
参数的传递：在某个地址按某种格式，存放好数据
uboot引导linux内核之do_bootm解析：
do_bootm
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;
s = getenv ("verify"); //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。
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；否则使用第二个参数作为加载地址。
addr = load_addr;
} else {
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
memmove (&header, (char *)addr, sizeof(image_header_t));//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
if (ntohl(hdr->ih_magic) != IH_MAGIC) { //判断文件头中的幻数是否为IH_MAGIC，所以如果不是u-boot镜像格式，会输出提示信息”Bad Magic Number”
#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);
checksum = ntohl(hdr->ih_hcrc); //对镜像头做crc校验
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) { //对镜像的数据部分做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;
#if defined(__PPC__) //校验cpu类型是否正确
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) { //根据镜像的压缩类型把内核镜像解压到指定的地址，一般是mkimage时-a指定的
那个地址，-a指定的那个地址也就是存储在镜像头里面的hdr->ih_load变量中，
什么时候指定的呢，其实就是在执行mkimage指令的时候，-a输入的时候，赋给的数值
case IH_COMP_NONE:
if(ntohl(hdr->ih_load) == addr) { //如果image header中指示的加载地址和bootm命令中参数2指定的地址相同，则表示不需要copy，可以就地执行。
printf (" XIP %s ... ", name);
} 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) */如果image header中指示的加载地址和bootm命令中参数2指定的地址不相同，则表示要从image header中指示的加载地址处把image data copy到bootm命令中参数2指定的地址处，然后再执行。
memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
#endif /* CONFIG_HW_WATCHDOG || CONFIG_WATCHDOG */
}
break;
case IH_COMP_GZIP:
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
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) {
default:
/* handled by (original) Linux case */
case IH_OS_LINUX:
#ifdef CONFIG_SILENT_CONSOLE
fixup_silent_linux();
#endif //这个函数接下来做进一步的跳转前的准备工作，在这之前，就是各种校验和数据解压拷贝工作。
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;
}
先来引用一下这篇介绍“ARM Linux内核启动要求”的文章ARM Linux Kernel Boot Requirements，是ARM Linux内核的维护者Russell King写的。
引用：
* CPU register settings
o r0 = 0.
o r1 = machine type number.
o r2 = physical address of tagged list in system RAM.
* CPU mode
o All forms of interrupts must be disabled (IRQs and FIQs.)
o The CPU must be in SVC mode. (A special exception exists for Angel.)
* Caches, MMUs
o The MMU must be off.
o Instruction cache may be on or off.
o Data cache must be off and must not contain any stale data.
* Devices
o DMA to/from devices should be quiesced.
* The boot loader is expected to call the kernel image by jumping directly to the first instruction of the kernel image.
下面对do_bootm_linux函数做一下注释，便于大家理解boot的过程。
void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
ulong addr, ulong *len_ptr, int verify)
{
ulong len = 0, checksum;
ulong initrd_start, initrd_end;
ulong data;
void (*theKernel)(int zero, int arch, uint params);
image_header_t *hdr = &header;
bd_t *bd = gd->bd;
#ifdef CONFIG_CMDLINE_TAG
char *commandline = getenv ("bootargs");
#endif
//可以看到theKernel被赋值为hdr->ih_ep，这个hdr是指使用tools/mkimage工具程
//序制作uImage时加在linux.bin.gz前面的一个头部，而ih_ep结构体成员保存的就是使用mkimage时指定
//的-e参数的值，即内核的入口点（Entry Point）。知道了hdr->ih_ep的意义之后，给theKernel赋这个
//值也就是理所当然的了。
theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
/*
* Check if there is an initrd image
*/
if (argc >= 3) {
SHOW_BOOT_PROGRESS (9);
addr = simple_strtoul (argv[2], NULL, 16);
printf ("## Loading Ramdisk 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
memcpy (&header, (char *) addr,
sizeof (image_header_t));
if (ntohl (hdr->ih_magic) != IH_MAGIC) {
printf ("Bad Magic Number\n");
SHOW_BOOT_PROGRESS (-10);
do_reset (cmdtp, flag, argc, argv);
}
data = (ulong) & header;
len = sizeof (image_header_t);
checksum = ntohl (hdr->ih_hcrc);
hdr->ih_hcrc = 0;
if (crc32 (0, (unsigned char *) data, len) != checksum) {
printf ("Bad Header Checksum\n");
SHOW_BOOT_PROGRESS (-11);
do_reset (cmdtp, flag, argc, argv);
}
SHOW_BOOT_PROGRESS (10);
print_image_hdr (hdr);
data = addr + sizeof (image_header_t);
len = ntohl (hdr->ih_size);
#ifdef CONFIG_HAS_DATAFLASH
if (addr_dataflash (addr)) {
read_dataflash (data, len, (char *) CFG_LOAD_ADDR);
data = CFG_LOAD_ADDR;
}
#endif
if (verify) {
ulong csum = 0;
printf (" Verifying Checksum ... ");
csum = crc32 (0, (unsigned char *) data, len);
if (csum != ntohl (hdr->ih_dcrc)) {
printf ("Bad Data CRC\n");
SHOW_BOOT_PROGRESS (-12);
do_reset (cmdtp, flag, argc, argv);
}
printf ("OK\n");
}
SHOW_BOOT_PROGRESS (11);
if ((hdr->ih_os != IH_OS_LINUX) ||
(hdr->ih_arch != IH_CPU_ARM) ||
(hdr->ih_type != IH_TYPE_RAMDISK)) {
printf ("No Linux ARM Ramdisk Image\n");
SHOW_BOOT_PROGRESS (-13);
do_reset (cmdtp, flag, argc, argv);
}
#if defined(CONFIG_B2) || defined(CONFIG_EVB4510) || defined(CONFIG_ARMADILLO)
/*
*we need to copy the ramdisk to SRAM to let Linux boot
*/
memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
data = ntohl(hdr->ih_load);
#endif /* CONFIG_B2 || CONFIG_EVB4510 */
/*
* Now check if we have a multifile image
*/
} else if ((hdr->ih_type == IH_TYPE_MULTI) && (len_ptr[1])) {
ulong tail = ntohl (len_ptr[0]) % 4;
int i;
SHOW_BOOT_PROGRESS (13);
/* skip kernel length and terminator */
data = (ulong) (&len_ptr[2]);
/* skip any additional image length fields */
for (i = 1; len_ptr[i]; ++i)
data += 4;
/* add kernel length, and align */
data += ntohl (len_ptr[0]);
if (tail) {
data += 4 - tail;
}
len = ntohl (len_ptr[1]);
} else {
/*
* no initrd image
*/
SHOW_BOOT_PROGRESS (14);
len = data = 0;
}
#ifdef DEBUG
if (!data) {
printf ("No initrd\n");
}
#endif
if (data) {
initrd_start = data;
initrd_end = initrd_start + len;
} else {
initrd_start = 0;
initrd_end = 0;
}
SHOW_BOOT_PROGRESS (15);
debug ("## Transferring control to Linux (at address %08lx) ...\n",
(ulong) theKernel);
#if defined (CONFIG_SETUP_MEMORY_TAGS) || \
defined (CONFIG_CMDLINE_TAG) || \
defined (CONFIG_INITRD_TAG) || \
defined (CONFIG_SERIAL_TAG) || \
defined (CONFIG_REVISION_TAG) || \
defined (CONFIG_LCD) || \
defined (CONFIG_VFD)
setup_start_tag (bd);
#ifdef CONFIG_SERIAL_TAG
setup_serial_tag (¶ms);
#endif
#ifdef CONFIG_REVISION_TAG
setup_revision_tag (¶ms);
#endif
#ifdef CONFIG_SETUP_MEMORY_TAGS
setup_memory_tags (bd);
#endif
#ifdef CONFIG_CMDLINE_TAG
setup_commandline_tag (bd, commandline);
#endif
#ifdef CONFIG_INITRD_TAG
if (initrd_start && initrd_end)
setup_initrd_tag (bd, initrd_start, initrd_end);
#endif
#if defined (CONFIG_VFD) || defined (CONFIG_LCD)
setup_videolfb_tag ((gd_t *) gd);
#endif
setup_end_tag (bd);
#endif
/* we assume that the kernel is in place */
printf ("\nStarting kernel ...\n\n");
#ifdef CONFIG_USB_DEVICE
{
extern void udc_disconnect (void);
//udc_disconnect (); // cancled by www.embedsky.net
}
#endif
cleanup_before_linux ();
//看看它的名字和参数的命名我们也可以猜到这个其实就是内核的入口函
//数的指针了。几个参数的命名也说明了上文提到的ARM Linux内核启动要求的第一条，
//因为根据ACPS（ARM/Thumb Procedure Call Standard）的规定，这三个参数就是依次
//使用r0，r1和r2来传递的。
调用的时候对参数进行赋值，r0=0，r1=bd->bi_arch_number，r2=bd->bi_boot_params，
一个都不少。至此U-Boot的使命完成，linux开始统治整个世界。
theKernel (0, bd->bi_arch_number, bd->bi_boot_params);
}
bootm命令是用来引导经过u-boot的工具mkimage打包后的kernel image的，什么叫做经
过u-boot的工具mkimage打包后的kernel image，这个就要看mkimage的用法:
mkimage的用法
uboot源代码的tools/目录下有mkimage工具，这个工具可以用来制作不压缩或者压缩的多种可启动映象文件。
mkimage在制作映象文件的时候，是在原来的可执行映象文件的前面加上一个0x40字节的头，记录参数所指定的信息，这样uboot才能识别这个映象是针对哪个CPU体系结构的，哪个OS的，哪种类型，加载内存中的哪个位置， 入口点在内存的那个位置以及映象名是什么
引用：
root@Glym:/tftpboot# ./mkimage
Usage: ./mkimage -l image
-l ==> list image header information
./mkimage -A arch -O os -T type -C comp -a addr -e ep -n name -d data_file[:data_file...] image
-A ==> set architecture to 'arch'
-O ==> set operating system to 'os'
-T ==> set image type to 'type'
-C ==> set compression type 'comp'
-a ==> set load address to 'addr' (hex)
-e ==> set entry point to 'ep' (hex)
-n ==> set image name to 'name'
-d ==> use image data from 'datafile'
-x ==> set XIP (execute in place)
参数说明：
-A 指定CPU的体系结构：
取值 表示的体系结构
alpha Alpha
arm A RM
x86 Intel x86
ia64 IA64
mips MIPS
mips64 MIPS 64 Bit
ppc PowerPC
s390 IBM S390
sh SuperH
sparc SPARC
sparc64 SPARC 64 Bit
m68k MC68000
-O 指定操作系统类型，可以取以下值：
openbsd、netbsd、freebsd、4_4bsd、linux、svr4、esix、solaris、irix、sco、dell、ncr、lynxos、vxworks、psos、qnx、u-boot、rtems、artos
-T 指定映象类型，可以取以下值：
standalone、kernel、ramdisk、multi、firmware、script、filesystem
-C 指定映象压缩方式，可以取以下值：
none 不压缩
gzip 用gzip的压缩方式
bzip2 用bzip2的压缩方式
-a 指定映象在内存中的加载地址，映象下载到内存中时，要按照用mkimage制作映象时，这个参数所指定的地址值来下载
-e 指定映象运行的入口点地址，这个地址就是-a参数指定的值加上0x40（因为前面有个mkimage添加的0x40个字节的头）
-n 指定映象名
-d 指定制作映象的源文件
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