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_TAG char *commandline = getenv("bootargs"); #endif 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 */ 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_TAG setup_serial_tag(¶m); #endif #ifdef CONFIG_REVISION_TAG setup_revision_tag(¶m); #endif #ifdef CONFIG_SETUP_MEMORY_TAG 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 setup_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。