Skip to content

Latest commit

 

History

History
26 lines (24 loc) · 1.38 KB

specifications.md

File metadata and controls

26 lines (24 loc) · 1.38 KB
Raw

Specifications

KRaBs supports only the minimal x86 Linux boot protocol.
Before attempting to use KRaBs for loading and booting your OS, take action as needed to meet the following requirements:

32bit boot protocol

  • At entry, the CPU is in 32-bit protected mode with paging disabled.
  • A GDT is loaded with the descriptors for selectors __BOOT_CS(0x10) and __BOOT_DS(0x18). Both descriptors is 4G flat segment. __BOOT_CS has execute/read permission, and __BOOT_DS has read/write permission.
  • CS is __BOOT_CS and DS, ES, SS is __BOOT_DS.
  • Interrupt is disabled.
  • %ebp, %edi and %ebx is zero.
  • %esi holds the base physical address(0x7C00) of the struct boot_params.

64bit boot protocol

  • At entry, the CPU is in 64-bit mode with paging enabled.
  • A GDT is loaded with the descriptors for selectors __BOOT_CS(0x10) and __BOOT_DS(0x18). Both descriptors is 4G flat segment. __BOOT_CS has execute/read permission, and __BOOT_DS has read/write permission.
  • CS is __BOOT_CS and DS, ES, SS is __BOOT_DS.
  • Interrupt is disabled.
  • %rsi holds the base physical address(0x7C00) of the struct boot_params.