1?headers.S:bootsect_start
bootsect_start
start2?? (0)
_start?? (512)
start_of_setup
void main(void) : main.c

2?main.c:main->go_to_protected_mode
go_to_protected_mode()

pm.c: -> protected_mode_jump->code32_start
?protected_mode_jump(boot_params.hdr.code32_start,
?????? (u32)&boot_params + (ds() << 4));
跳转到header.S中定义的code32_start：
code32_start:????# here loaders can put a different
?????# start address for 32-bit code.
#ifndef __BIG_KERNEL__
??.long?0x1000??#?? 0x1000 = default for zImage
#else
??.long?0x100000?# 0x100000 = default for big kernel
#endif
此处对应head_32.S

3?head_32.S:startup_32/decompress_kernel/jmp
startup_32
...
/*
?* Do the decompression, and jump to the new kernel..
?*/
...
?call decompress_kernel
...
/*
?* Jump to the decompressed kernel.
?*/
?xorl %ebx,%ebx
?jmp *%ebp

应该是跳转到了arch/i386/kernel/head_32.S

4?head_32.S:startup_32
ENTRY(startup_32)
...
ENTRY(initial_code)
?.long i386_start_kernel
...

head32.c:i386_start_kernel
void __init i386_start_kernel(void)
{
?start_kernel();
}

5?init/main.c:start_kernel
start_kernel()