简介在Source Debug功能未就绪前。我们可以通过串口输出一些信息便于我们追踪和分析代码。SerialDebug.asmOVMF在SerialDebug.asm中提供了初始化串口的功能默认未加载相关代码。根据ResetVector.nasmbOvmfPkg\ResetVector\ResetVector.nasmb中代码逻辑我们只需定义宏DEBUG_SERIAL即可如下%define DEBUG_SERIAL %ifdef DEBUG_PORT80 %include Port80Debug.asm %elifdef DEBUG_SERIAL %include SerialDebug.asm %elif 0 ; Set ^ this to 1 to enable postcodes on the qemu debug console. ; Disabled by default because it is incompatible with SEV-ES/SEV-SNP and TDX. %include QemuDebugCon.asm %else %include DebugDisabled.asm %endif配置初始化串口函数debugInitializeOVMF平台默认在函数EarlyInit16中才初始化串口使用函数debugInitialize。我们可以将它提前理论上CPU可以执行指令后就可以初始化串口了。因此我们将debugInitialize放在EarlyBspInitReal16处即可如下; ; param[out] DI BP to indicate boot-strap processor ; EarlyBspInitReal16: debugInitialize mov di, BP jmp short Main16这样我们从EarlyBspInitReal16就可以打印信息道串口了比如; ; param[out] DI BP to indicate boot-strap processor ; EarlyBspInitReal16: debugInitialize debugShowCharacter J debugShowCharacter a debugShowCharacter s debugShowCharacter o debugShowCharacter n debugShowCharacter S debugShowCharacter t debugShowCharacter u debugShowCharacter d debugShowCharacter y debugShowCharacter : debugShowCharacter debugShowCharacter E debugShowCharacter a debugShowCharacter r debugShowCharacter l debugShowCharacter y debugShowCharacter B debugShowCharacter s debugShowCharacter p debugShowCharacter I debugShowCharacter n debugShowCharacter i debugShowCharacter t debugShowCharacter R debugShowCharacter e debugShowCharacter a debugShowCharacter l debugShowCharacter y debugShowCharacter 1 debugShowCharacter 6 debugNewline mov di, BP jmp short Main16串口输出如下JasonStudy: EarlyBspInitRealy161632b1 f1 SecCoreStartupWithStack(0xFFFCC000, 0x820000)Debug Timer: FSB Clock1000000000Debug Timer: Divisor2Debug Timer: Frequency500000000Debug Timer: InitialCount50000000Send INITbreakpacket and try to connect the HOST(Intel(R)UDK Debugger Tool v1.5)...debugInitialize这个函数用于初始化串口0x3f8主要在相应的串口寄存器中配置以下信息设置数据格式配置波特率;//--------------------------------------------- ;// UART Register Offsets ;//--------------------------------------------- %define BAUD_LOW_OFFSET 0x00 %define BAUD_HIGH_OFFSET 0x01 %define IER_OFFSET 0x01 %define LCR_SHADOW_OFFSET 0x01 %define FCR_SHADOW_OFFSET 0x02 %define IR_CONTROL_OFFSET 0x02 %define FCR_OFFSET 0x02 %define EIR_OFFSET 0x02 %define BSR_OFFSET 0x03 %define LCR_OFFSET 0x03 %define MCR_OFFSET 0x04 %define LSR_OFFSET 0x05 %define MSR_OFFSET 0x06 ;//--------------------------------------------- ;// UART Register Bit Defines ;//--------------------------------------------- %define LSR_TXRDY 0x20 %define LSR_RXDA 0x01 %define DLAB 0x01 %define DEFAULT_COM_BASE 0x3f8 %define DEFAULT_BPS 115200 %define DEFAULT_DATA 8 %define DEFAULT_STOP 1 %define DEFAULT_PARITY 0 %define DEFAULT_BREAK_SET 0 %define SERIAL_DEFAULT_LCR ( \ (DEFAULT_BREAK_SET 6) | \ (DEFAULT_PARITY 3) | \ (DEFAULT_STOP 2) | \ (DEFAULT_DATA - 5) \ ) %define SERIAL_PORT_IO_BASE_ADDRESS DEFAULT_COM_BASE %macro outToSerialPort 2 mov dx, (SERIAL_PORT_IO_BASE_ADDRESS %1) mov al, %2 out dx, al %endmacro %macro debugInitialize 0 jmp real16InitDebug real16InitDebugReturn: %endmacro real16InitDebug: ; ; Set communications format ; outToSerialPort LCR_OFFSET, ((DLAB 7) | SERIAL_DEFAULT_LCR) ; ; Configure baud rate ; outToSerialPort BAUD_HIGH_OFFSET, ((115200 / DEFAULT_BPS) 8) outToSerialPort BAUD_LOW_OFFSET, ((115200 / DEFAULT_BPS) 0xff) ; ; Switch back to bank 0 ; outToSerialPort LCR_OFFSET, SERIAL_DEFAULT_LCR jmp real16InitDebugReturn