Relocate the kernel

Reposition the program in the elf file segment by segment

;initKernel ---------------------------------------------------------------------------------
; 将 KERNEL.BIN 的内容经过整理对齐后放到新的位置
; 遍历每一个 Program Header，根据 Program Header 中的信息来确定把什么放进内存，放到什么位置，以及放多少。
; --------------------------------------------------------------------------------------------
InitKernel:
        xor   esi, esi
        mov   cx, word [BaseOfKernelFilePhyAddr+2Ch];`. ecx <- pELFHdr->e_phnum
        movzx ecx, cx                               ;/
        mov   esi, [BaseOfKernelFilePhyAddr + 1Ch]  ; esi <- pELFHdr->e_phoff
        add   esi, BaseOfKernelFilePhyAddr;esi<-OffsetOfKernel+pELFHdr->e_phoff
.Begin:
        mov   eax, [esi + 0]
        cmp   eax, 0                      ; PT_NULL
        jz    .NoAction
        push  dword [esi + 010h]    ;size ;`.
        mov   eax, [esi + 04h]            ; |
        add   eax, BaseOfKernelFilePhyAddr; | memcpy((void*)(pPHdr->p_vaddr),
        push  eax           ;src  ; |      uchCode + pPHdr->p_offset,
        push  dword [esi + 08h]     ;dst  ; |      pPHdr->p_filesz;
        call  MemCpy                      ; |
        add   esp, 12                     ;/
.NoAction:
        add   esi, 020h                   ; esi += pELFHdr->e_phentsize
        dec   ecx
        jnz   .Begin

        ret
; InitKernel

Then jump to the kernel

call    InitKernel
jmp SelectorFlatC:KernelEntryPointPhyAddr   ; 正式进入内核

elf file compilation needs to set the entry address

nasm -f elf -o kernel.o kernel.asm
ld -m elf_i386 -s -Ttext 0x30400 -o kernel.bin kernel.o