U-Boot启动Linux内核

1、U_BOOT_CMD（
bootm, CFG_MAXARGS, 1,do_bootm,
"bootm - boot application image from memory ",
"[addr [arg ...]] - boot application image stored in memory "
" passing arguments "arg ..."; when booting a Linux kernel, "
" "arg" can be the address of an initrd image "
#ifdef CONFIG_OF_FLAT_TREE
" When booting a Linux kernel which requires a flat device-tree "
" a third argument is required which is the address of the of the "
" device-tree blob. To boot that kernel without an initrd image, "
" use a "-" for the second argument. If you do not pass a third "
" a bd_info struct will be passed instead "
#endif
）;
根据上面可知：bootm命令的执行函数是do_bootm，函数的最大参数是CFG_MAXARGS。U-Boot源代码下载地址 http://www.linuxidc.com/Linux/2011-07/38897.htm2、do_bootm函数源码摘要：SHOW_BOOT_PROGRESS （8）;

#if defined（CONFIG_ZIMAGE_BOOT） || defined（CONFIG_IMAGE_BOOT）
after_header_check:
#endif
switch （hdr->ih_os） {
default: /* handled by （original） Linux case */
case IH_OS_LINUX:
#ifdef CONFIG_SILENT_CONSOLE
fixup_silent_linux（）;
#endif
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
}
可知，do_bootm函数调用do_bootm_linux函数启动Linux内核，当定义了CONFIG_PPC是，将使用common/cmd_bootm.c文件中的do_bootm_linux;当没有定义时，将调用lib_arm/armlinux.c文件中的do_bootm_linux函数。