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

接著跳到Init16.asm再跳到Main.asm裡面Main16這個位址

Main16:       OneTimeCall EarlyInit16       ;       ; Transition the processor from 16-bit real mode to 32-bit flat mode       ;       OneTimeCall TransitionFromReal16To32BitFlat BITS    32       ;       ; Search for the Boot Firmware Volume (BFV)       ;       OneTimeCall Flat32SearchForBfvBase       ;       ; EBP - Start of BFV       ;       ;       ; Search for the SEC entry point       ;       OneTimeCall Flat32SearchForSecEntryPoint       ;       ; ESI - SEC Core entry point       ; EBP - Start of BFV       ; %ifdef ARCH_IA32       ;       ; Restore initial EAX value into the EAX register       ;       mov     eax, esp       ;       ; Jump to the 32-bit SEC entry point       ;       jmp     esi (略)