UEFI : PEI Phase Code Trace

$ PEI (Pre Efi Initialization)的概述:

● Small, tight startup code

• Startup with transitory memory store for call-stack (I.e., cache)       

• XIP from ROM

● Core locates, validates, and dispatches PEIMs

● Publishes own protocol and call-abstraction with PPI

• Silicon/platform abstractions

● Primary goals

• Discover boot mode       

• Launch modules that initialize main memory       

• Discovery & launch DXE core- Convey platform info into DXE

UEFI : SEC Phase Code Trace

UEFI 架構只有SEC這個phase因為是machine dependent而且cache/memory尚未初始化，所以剛開始是組合語言寫的，最主要就是做以下這幾件事:

1. 切32位元(或64位元)flat mode
2. Cache As Ram (在Flat32.asm中jump到CacheAsRam函數的位址)
3. 找BFV(Boot Firmware Volume), BFV指的是存放PEI Foundation/PEIMs的FV
4. 找到以C寫的SEC phase entry point
5. 跳到以C code寫的SEC point (SecStartup)，最後Transfer the control to the PEI core

VOID EFIAPI SecStartup (   IN UINT32    SizeOfRam,   IN UINT32    TempRamBase,   IN VOID      *BootFirmwareVolume   ) {    ... }

從上電的reset vector, trace Code如下:

進入點為 UefiCpuPkg\ResetVector\Vtf0\Ia16\ResetVectorVtf0.asm

;; Reset Vector ; ; This is where the processor will begin execution ;     nop     nop     jmp     short EarlyBspInitReal16