Appendix

Appendix

The boot page table

Linear-Address Translation to 2-MByte Pages using 4-Level Paging(1:1)

• ptl2: 2MB * 2048 page tables entries. Each page table entry is 8Bytes. 4 pages.
• ptl3: 4 page table entries and each points to a ptl3 page.
• ptl4: 1 page table entry that points to ptl3.

Multiboot Specification

Getting the memory map of the machine provided by the BIOS

MultiProcessor Specification

Detecting the number of PCPU

• Search for the MP Floating Pointer Structure, which according to MultiProcessor Specification is in one of the following three locations:
  1. in the first KB of the EBDA;
  2. in the last KB of system base memory;
  3. in the BIOS ROM between 0xE0000 and 0xFFFFF.
• Search for an MP configuration table.

BDA & EBDA

当计算机通电时，BIOS数据区（BIOS Data Area）将在000400h处创建。它长度为256字节（000400h - 0004FFh），包含有关系统环境的信息。该信息可以被任何程序访问和更改。计算机的大部分操作由此数据控制。此数据在启动过程中由POST（BIOS开机自检）加载。

如果EBDA（Extended BIOS Data Area,扩展BIOS数据区）不存在，BDA[0x0E]和BDA[0x0F]的值为0；如果EBDA存在，其段地址被保存在BDA[0x0E]和BDA[0x0F]中，其中BDA[0x0E]保存EBDA段地址的低8位，BDA[0x0F]保存EDBA段地址的高8位，所以(BDA[0x0F] << 8) | BDA[0x0E]就表示了EDBA的段地址，将段地址左移4位即为EBDA的物理地址。在HyperBench中，BDA[0x0F]=0x9F，BDA[0x0E]=0xC0，所以EBDA存在且段地址为0x9FC0，物理地址为0x9FC00。