Linux内核启动：setup_arch

BootLoader 可以向Linux 传递参数，编译内核时也可以配置boot options 。

调试中使用的U-Boot bootargs如下：

noinitrd root=/dev/mtdblock3 rw console=ttySAC0,115200 init=/linuxrc mem=64M

内核版本：

2.6.35.7

内核的处理参数的整体过程如下：

① u-boot将配置参数地址通过寄存器传递给内核

② 内核(arch/arm/kernel/head-common.S中的 __mmap_switched)将这个地址存入__atags_pointer(定义于arch/arm/kernel/setup.c)

③ setup_arch() 函数

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<span style="font-size: 14px;">void __init setup_arch(char **cmdline_p)

{

struct tag *tags = (struct tag *)&init_tags;

struct machine_desc *mdesc;

char *from = default_command_line; 编译内核时配置的Boot Options

unwind_init();

setup_processor();

mdesc = setup_machine(machine_arch_type);

machine_name = mdesc->name;

if (mdesc->soft_reboot)

reboot_setup("s");

if (__atags_pointer) 检查BootLoader是否传入参数

tags = phys_to_virt(__atags_pointer);

else if (mdesc->boot_params)

tags = phys_to_virt(mdesc->boot_params); machine descriptor中传入的启动参数地址(arch/arm/mach-s3c2440/mach-mini2440.c)

/*

* If we have the old style parameters, convert them to

* a tag list.

*/

if (tags->hdr.tag != ATAG_CORE)

convert_to_tag_list(tags);

if (tags->hdr.tag != ATAG_CORE)

tags = (struct tag *)&init_tags; 使用default init_tags，其中内存的定义是: 起始地址：0x30000000，大小是16M

if (mdesc->fixup)

mdesc->fixup(mdesc, tags, &from, &meminfo);

if (tags->hdr.tag == ATAG_CORE) {

if (meminfo.nr_banks != 0) 如果内存已经初始化，则忽略mem TAG

squash_mem_tags(tags);

save_atags(tags);

parse_tags(tags); 解析TAGS，其中如果U-boot传入ATAG_CMDLINE，则使用U-boot传入的bootargs覆盖default_command_line

}

init_mm.start_code = (unsigned long) _text;

init_mm.end_code = (unsigned long) _etext;

init_mm.end_data = (unsigned long) _edata;

init_mm.brk = (unsigned long) _end;

/* parse_early_param needs a boot_command_line */

strlcpy(boot_command_line, from, COMMAND_LINE_SIZE); 将defualt_command_line拷入boot_command_line

/* populate cmd_line too for later use, preserving boot_command_line */

strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);

*cmdline_p = cmd_line;

parse_early_param(); 大部分参数的early属性为0，即大部分参数在早期不处理，如noinitrd，console等

paging_init(mdesc);

request_standard_resources(&meminfo, mdesc);

***************

</span>

}

void __init setup_arch(char **cmdline_p)

{
struct tag *tags = (struct tag *)&init_tags;
struct machine_desc *mdesc;
char *from = default_command_line; 编译内核时配置的Boot Options

unwind_init();

setup_processor();
mdesc = setup_machine(machine_arch_type);
machine_name = mdesc->name;

if (mdesc->soft_reboot)
reboot_setup("s");

if (__atags_pointer)                                               检查BootLoader是否传入参数
tags = phys_to_virt(__atags_pointer);
else if (mdesc->boot_params)
tags = phys_to_virt(mdesc->boot_params);  machine descriptor中传入的启动参数地址(arch/arm/mach-s3c2440/mach-mini2440.c)

/*
* If we have the old style parameters, convert them to
* a tag list.
*/
if (tags->hdr.tag != ATAG_CORE)
convert_to_tag_list(tags);
if (tags->hdr.tag != ATAG_CORE)
tags = (struct tag *)&init_tags;       使用default init_tags，其中内存的定义是: 起始地址：0x30000000，大小是16M

if (mdesc->fixup)
mdesc->fixup(mdesc, tags, &from, &meminfo);

if (tags->hdr.tag == ATAG_CORE) {
if (meminfo.nr_banks != 0)                如果内存已经初始化，则忽略mem TAG
squash_mem_tags(tags);
save_atags(tags);
parse_tags(tags);             解析TAGS，其中如果U-boot传入ATAG_CMDLINE，则使用U-boot传入的bootargs覆盖default_command_line
}

init_mm.start_code = (unsigned long) _text;
init_mm.end_code   = (unsigned long) _etext;
init_mm.end_data   = (unsigned long) _edata;
init_mm.brk        = (unsigned long) _end;

/* parse_early_param needs a boot_command_line */
strlcpy(boot_command_line, from, COMMAND_LINE_SIZE);         将defualt_command_line拷入boot_command_line

/* populate cmd_line too for later use, preserving boot_command_line */
strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
*cmdline_p = cmd_line;

parse_early_param();               大部分参数的early属性为0，即大部分参数在早期不处理，如noinitrd，console等

paging_init(mdesc);
request_standard_resources(&meminfo, mdesc);

***************

}

一．u-boot传递TAG到kernel的解析

在setup_arch函数的parse_tags中对传递过来的TAGLIST进行了解析

对每一项的tag使用parse_tag分析，

for (t = &__tagtable_begin; t < &__tagtable_end; t++)

if (tag->hdr.tag == t->tag) {

t->parse(tag);

break;

}

其中__tagtable_begin,__tagtable_end在vmlinux.ld中也有定义，这里看tagtable的建立过程

#define __tagtalbe(tag,fn)/

Static struct tagtable __tagtable_##fn __tag={tag,fn}

#define __tag __userd __attribute__((__section__(“.taglist.init”)))

对于上述宏中的fn,就是tagtable结构中的parse指针所指向的函数。

而在setup.c中，已经通过__tagtalbe(ATAG_XXX,XXX)建立起所有可能的tagtable,所以可以通过遍历__tagtable_begin~__tagtable_end找到对应的tagtable,并调用对应的parse进行解析并配置