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I am a beginner and writing assembly program to print numbers from 1 to 9 using this code: section .text global _start _start: mov ecx,10 mov eax, '1' l1: mov [num], eax mov eax, 4 mov ebx, 1 push ecx mov ecx, num mov edx, 1 int 0x80 mov eax, [num] sub eax, '0' inc eax add eax, '0' pop ecx loop l1 mov eax,1 ;system call number (sys_exit) int 0x80 ;call kernel section .bss num resb 1
mov esi, [ebp+8] begin: xor ecx, ecx mov eax, [esi] The second instruction in this code fragment is labeled begin. Elsewhere in the code, we can refer to the memory location that this instruction is located at in memory using the more convenient symbolic name begin. This label is just a convenient way of expressing the location instead of its ...
"mov" is an instruction, encoded with the operation code or "opcode" 0xb8. Since mov takes an argument, the next 4 bytes are the constant to move into eax. The opcode 0xb9 moves a constant into ecx. 0xba moves a constant into edx.
mov eax, 3 mov ecx, 7 add eax, ecx ret (executable NetRun link) Here are the x86 arithmetic instructions. Note that they *all* take just two registers, the destination and the source. Opcode: Does: Example: add + add eax,ecx: sub-sub eax,ecx: imul * imul eax,ecx: idiv / idiv ecx <- Warning! Weirdness! (see below)
mov edx,len mov ecx,msg mov ebx,1 mov eax,4 int 0x80 mov eax,1 int 0x80 section .data msg db 'Hello, world!', 0xa len equ $ - msg Someone pls explain what it means. Some article says that it is just the register, if so provide some resource to understand better. Locked post. New comments cannot be posted.
section .text global _start ;must be declared for using gcc _start: ;tell linker entry point ;create the file mov eax, 8 mov ebx, file_name mov ecx, 0777 ;read, write and execute by all int 0x80 ;call kernel mov [fd_out], eax ; write into the file mov edx,len ;number of bytes mov ecx, msg ;message to write mov ebx, [fd_out] ;file descriptor mov ...
mov eax,1 ; system call number (sys_exit) int 0x80 ; call kernel The following code snippet shows the use of the system call sys_write − mov edx,4 ; message length mov ecx,msg ; message to write mov ebx,1 ; file descriptor (stdout) mov eax,4 ; system call number (sys_write) int 0x80 ; call kernel
; print a byte to stdout mov eax, 4; the system interprets 4 as "write" mov ebx, 1; standard output (print to terminal) mov ecx, variable; pointer to the value being passed mov edx, 1; length of output (in bytes) int 0x80; call the kernel. BSD systems (MacOS X included) use similar system calls, but convention to execute them is different ...
mov ecx, 0 mov cx, count; ECX is 0 Copying Smaller Values into Larger Ones • What happens if we write:.data signedVal SWORD -1.code mov ecx, 0 mov cx, SignedVal; ECX is ; 0000FFF0h; (+65520) • We could solve the problem by writing: mov ecx, FFFFFFFFx mov cx, signedVal ; ECX=FFFFFFF0h
The LOOP instruction assumes that the ECX register contains the loop count. When the loop instruction is executed, the ECX register is decremented and the control jumps to the target label, until the ECX register value, i.e., the counter reaches the value zero. The above code snippet could be written as −. mov ECX,10 l1: loop l1 ...