assembly

问题 I'm trying to Is there any good resource available to learn 'decoding' of i386 opcodes? Most of the websites talk about how to encode instructions, but I don't find anywhere something telling as to how to decode opcodes to instructions. I've looked at the source code of some disassemblers, but I want some documentation as to how to decode opcodes to instructions. Thanks and Regards, Hrishikesh Murali 回答1: Read the processor manuals, they have it described, though maybe not in complete details

问题 I'm trying to Is there any good resource available to learn 'decoding' of i386 opcodes? Most of the websites talk about how to encode instructions, but I don't find anywhere something telling as to how to decode opcodes to instructions. I've looked at the source code of some disassemblers, but I want some documentation as to how to decode opcodes to instructions. Thanks and Regards, Hrishikesh Murali 回答1: Read the processor manuals, they have it described, though maybe not in complete details

问题 I'm trying to Is there any good resource available to learn 'decoding' of i386 opcodes? Most of the websites talk about how to encode instructions, but I don't find anywhere something telling as to how to decode opcodes to instructions. I've looked at the source code of some disassemblers, but I want some documentation as to how to decode opcodes to instructions. Thanks and Regards, Hrishikesh Murali 回答1: Read the processor manuals, they have it described, though maybe not in complete details

问题 Here is a very simple assembly program, just return 12 after executed. $ cat a.asm global _start section .text _start: mov rax, 60 ; system call for exit mov rdi, 12 ; exit code 12 syscall It can be built and executed correctly: $ nasm -f elf64 a.asm && ld a.o && ./a.out || echo $? 12 But the size of a.out is big, it is more than 4k: $ wc -c a.out 4664 a.out I try to understand it by reading elf content: $ readelf -l a.out Elf file type is EXEC (Executable file) Entry point 0x401000 There are

问题 Here is a very simple assembly program, just return 12 after executed. $ cat a.asm global _start section .text _start: mov rax, 60 ; system call for exit mov rdi, 12 ; exit code 12 syscall It can be built and executed correctly: $ nasm -f elf64 a.asm && ld a.o && ./a.out || echo $? 12 But the size of a.out is big, it is more than 4k: $ wc -c a.out 4664 a.out I try to understand it by reading elf content: $ readelf -l a.out Elf file type is EXEC (Executable file) Entry point 0x401000 There are

问题 I was trying to divide (Unsigned) 8A32F4D5 by C9A5 using emu8086 tool. I expected the quotient to be AF73H and the remainder be 94B6H . After writing the following code, I was getting correct quotient but the remainder became 0000h . Am I missing something? .MODEL SMALL .STACK 100H .DATA .CODE MAIN PROC ; initialize DS MOV AX,@DATA MOV DS,AX ; enter your code here MOV DX, 8A32H MOV AX, 0F4D5H MOV BX, 0C9A5H DIV BX ;exit to DOS MOV AX,4C00H INT 21H MAIN ENDP END MAIN The output in EMU8086: 回答1

问题 I was trying to divide (Unsigned) 8A32F4D5 by C9A5 using emu8086 tool. I expected the quotient to be AF73H and the remainder be 94B6H . After writing the following code, I was getting correct quotient but the remainder became 0000h . Am I missing something? .MODEL SMALL .STACK 100H .DATA .CODE MAIN PROC ; initialize DS MOV AX,@DATA MOV DS,AX ; enter your code here MOV DX, 8A32H MOV AX, 0F4D5H MOV BX, 0C9A5H DIV BX ;exit to DOS MOV AX,4C00H INT 21H MAIN ENDP END MAIN The output in EMU8086: 回答1

问题 I was trying to divide (Unsigned) 8A32F4D5 by C9A5 using emu8086 tool. I expected the quotient to be AF73H and the remainder be 94B6H . After writing the following code, I was getting correct quotient but the remainder became 0000h . Am I missing something? .MODEL SMALL .STACK 100H .DATA .CODE MAIN PROC ; initialize DS MOV AX,@DATA MOV DS,AX ; enter your code here MOV DX, 8A32H MOV AX, 0F4D5H MOV BX, 0C9A5H DIV BX ;exit to DOS MOV AX,4C00H INT 21H MAIN ENDP END MAIN The output in EMU8086: 回答1

问题 I code a simple program which loads the sector (sector num.2) to the RAM but prints nothing. first, I tried this code for bootsector: org 0x7c00 mov ax, 0x1000 ; ES:BX = 1000:0000 mov es, ax mov bx, 0x00 LoadSectortoMemory: mov al, 0x01 ; Load 1 sectors mov ah, 0x02 ; Load disk data to ES:BX mov cl, 0x02 ; Sector = 2 mov ch, 0x00 ; Cylinder = 0 mov dl, 0x00 ; Drive = 0 mov dh, 0x00 ; Head = 0 int 13h ; Read jc LoadSectortoMemory ; ERROR => Try again jmp 0x1000:0x0000 times 510-($-$$) db 0 dw

问题 I have a problem with my assembly code (64 bit masm in Visual 2013 on win8 64). When I'm calling C function (printf), it throwing exception from ntdll.dll. What I'm doing wrong? How I can read and write data from console in 64 bit masm? Where I can find good tutorial for masm 64 bit? extrn printf : proc .data format byte "Arg1: %d", 10, 0 .code printData proc mov rbx, 100 push rbx lea rax, format; format address push rax call printf; throw unhandled exception ntdll.dll - Access violation