U-Boot与内核的关系(3)

3. do_bootm_linux函数的实现

/* lib_arm/armlinux.c */void do_bootm_linux(cmd_tbl_t *cmtp, int flag, int argc, char *argv[],ulong addr, ulong *len_ptr, int verify){DECLARE_GLOBAL_DATA_PTR;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_TAGchar *commandline = getenv("bootargs");#endiftheKernel = (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 */memcpy(&header, (char *)addr, sizeof(image_header_t));if (ntohl(hdr->ih_magic) != IH_MAGIC) {printf("Bad Magic Number/n");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, (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);if (verify) {ulong csum = 0;printf(" Verifying Checksum ... ");csum = crc32(0, (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);}} /* 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;}if (data) {initrd_start = data;initrd_end = initrd_start + len;} else {initrd_start = 0;initrd_end = 0;}SHOW_BOOT_PROGRESS(15);debug("## Trasnferring control to Linux (at address %08lx).../n", (ulong)theKernel);#if defined(CONFIG_SETUP_MEMORY_TAGS) || /#define (CONFIG_CMDLINE_TAG) || /#define (CONFIG_INITRD_TAG) || /#define (CONFIG_SERIAL_TAG) || /#define (COFNIG_REVISION_TAG) || /#define (CONFIG_LCD) || /#define (CONFIG_VFG)setup_start_tag(bd);#ifdef CONFIG_SERIAL_TAGsetup_serial_tag(¶m);#endif#ifdef CONFIG_REVISION_TAGsetup_revision_tag(¶m);#endif#ifdef CONFIG_SETUP_MEMORY_TAGsetup_memory_tags(bd);#endif#ifdef CONFIG_CMDLINE_TAGsetup_commandline_tag(bd, commandline);#endif#ifdef CONFIG_INITRD_TAGif (initrd_start && initrd_end)setup_initrd_tag(bd, initrd_start, initrd_end);#endifsetup_end_tag(bd);#endif/*we asuume that the kernel is in place */printf("/nStarting Kernel .../n/n");cleanup_before_linux();theKernel(0, bd->bi_arch_number, bd->bi_boot_params);} 

do_bootm_linux()函数是专门引导Linux映像的函数，它还可以处理ramdisk文件系统的映像。这里引导的内核映像和ramdisk映像，必须是U-Boot格式的。U-Boot格式的映像可以通过mkImage工具来转换，其中包含了U-Boot可以识别的符号。