OVMF Boot Overview

This page provides a high-level overview of the boot process for OVMF.

SEC

• UefiCpuPkg/ResetVector/Vtf0
  • Ia16/ResetVectorVtf0.asm: Starts at resetVector
  • Ia16/Real16ToFlat32.asm: Mode Switch: Real => 32-bit Flat
  • Ia32/SearchForBfvBase.asm: Locates the Boot FirmwareVolume (BFV)
  • Ia32/SearchForSecEntry.asm: Locates the SEC Core with BFV
  • Ia32/Flat32ToFlat64.asm: If 64-bit PEI, then Mode Switch: 32-bit Flat to 64-bit Long
• SEC Core: OvmfPkg/Sec
  • OvmfPkg/Sec/SecMain.c: Finds PEI Core

PEI

Pre-EFI Initialization

• PEI Core: MdeModulePkg/Core/Pei
  • Various PEI drivers now run
• DXE IPL (Loader for the DXE Core)
  • Finds DXE Core
  • If PEI is 32-bit and DXE is 64-bit, then Mode Switch: 32-bit Flat to 64-bit Long
  • Jumps to DXE Core

DXE

Driver Execution Environment

• DXE Core: MdeModulePkg/Core/Dxe
  • Various DXE/UEFI drivers now run
  • BDS is run after all DXE architectural protocols are available

BDS

Boot Device Selection

• BDS: IntelFrameworkModulePkg/Universal/BdsDxe + IntelFrameworkModulePkg/Library/GenericBdsLib
  • OvmfPkg/Library/PlatformBdsLib guides BDS in a platform specific manner
• BDS figures out what to boot, and starts devices to enable the boot
  • BDS may be able to load the EFI shell if it is present in the system firmware file system