immediate-operand – Tarik Billa

Difference between movq and movabsq in x86-64

September 3, 2023 by Tarik

Unless your 64-bit value can be encoded as a 32-bit-sign-extended immediate, you have to move it to a register first and then store. (Or do two separate 32-bit stores, or other worse workaround to get the bytes where you want them.) In NASM / Intel syntax, mov r64, 0x… picks a MOV encoding based on … Read more

Why use LDR over MOV (or vice versa) in ARM assembly?

August 16, 2023 by Tarik

It is a trick/shortcut. say for example ldr r0,=main what would happen is the assembler would allocate a data word, near the instruction but outside the instruction path ldr r0,main_addr … b somewhere main_addr: .data main Now expand that trick to constants/immediates, esp those that cannot fit into a move immediate instruction: top: add r1,r2,r3 … Read more