U-Boot直接引导zImage内核

 

         U-boot1.1.6只能只能就能过mkimage工具加工后的内核镜像文件。mkimage工具给zImage增加了一个64B大小的头。U-Boot是通过bootm命令来引导Linux内核的，bootm命令调用do_bootm函数来mkimage工具增加的头，最后调用do_bootm_linux函数引导去掉了mkimage工具增加的头的Linux内核，也就是zImage，启动的流程可以参考图解U-Boot：引导内核分析这篇博客。

     要让U-Boot直接引导zImage内核，只需在do_bootm函数中去掉对mkimage工具增加的头的分析，直接调用do_bootm_linux函数引导zImage内核即可。下面是经过修改的do_bootm函数，修改的部分用///////////包围起来了，省略号后面的就不需要改动了。这个函数common/cmd_bootm.c文件中。

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");
    verify = (s && (*s == 'n')) ? 0 : 1;
    if (argc < 2) {
        addr = load_addr;
    } else {
        addr = simple_strtoul(argv[1], NULL, 16);
    }
    SHOW_BOOT_PROGRESS (1);
//////////////////////////////////////////////////////////////////////////////////
    //printf ("## Booting image at %08lx ...\n", addr);
    printf ("## Booting from zImage at %08lx ---by ce123\n", addr);
#ifdef CONFIG_SILENT_CONSOLE
        fixup_silent_linux();
#endif
        do_bootm_linux  (cmdtp, flag, argc, argv,
                 addr, len_ptr, verify);
//////////////////////////////////////////////////////////////////////////////////
......

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");
	verify = (s && (*s == 'n')) ? 0 : 1;
 	if (argc < 2) {
		addr = load_addr;
	} else {
		addr = simple_strtoul(argv[1], NULL, 16);
	}
 	SHOW_BOOT_PROGRESS (1);
//////////////////////////////////////////////////////////////////////////////////
	//printf ("## Booting image at %08lx ...\n", addr);
	printf ("## Booting from zImage at %08lx ---by ce123\n", addr);
#ifdef CONFIG_SILENT_CONSOLE
	    fixup_silent_linux();
#endif
	    do_bootm_linux  (cmdtp, flag, argc, argv,
			     addr, len_ptr, verify);
//////////////////////////////////////////////////////////////////////////////////
......

接下来还要修改一下lib_arm/armlinux.c中的do_bootm_linux函数。这里主要是修改kernal的加载地址（theKernel = (void (*)(int, int, uint))addr）。这就要求我们将zImage内核下载内存的addr处。并且用bootm addr进行引导，默认的地址是0x30008000，如果直接使用bootm进行引导，则需要将内核下载到0x30008000，否则无法引导内核。

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


    //theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
    theKernel = (void (*)(int, int, uint))addr;

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


	//theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
	theKernel = (void (*)(int, int, uint))addr;

下面是引导信息：

U-Boot 1.1.6 (Mar 11 2012 - 14:06:15)


DRAM:  64 MB
Flash:  2 MB
NAND:  256 MiB
In:    serial
Out:   serial
Err:   serial
Hit any key to stop autoboot:  0

NAND read: device 0 offset 0x240000, size 0x200000
2097152 bytes read: OK
## Booting from zImage at 30008000 ---by ce123

Starting kernel ...

Uncompressing Linux.............................................................
............................................................. done, booting the
kernel.