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Assembly

A family of programming languages that provide instructions close to machine code.

Learn

Intro:

• https://shikaan.github.io/assembly/x86/guide/2024/09/08/x86-64-introduction-hello.html
• https://shikaan.github.io/assembly/x86/guide/2024/09/16/x86-64-conditionals.html

Notes

• In x86-64 there are 16 general-purpose registers, each 8 byte wide.
• You can access the whole register or only a part of it (1 byte, 2 bytes, 4 bytes).
• rip is the instruction pointer register.
• File extensions: .s, .asm.
• File sections: .data (variables, optional), .rodata (constants, optional), .text (code, mandatory).
• File syntax: ; for comments, db to declare strings, equ to declare numbers.
• Declare a label with lbl:, reference it with lbl.
• Control Transfer Instruction (CTI) types: unconditional (e.g. jmp) and conditional (e.g. je, jg, jl).
• eflags is a 32-bit register that stores various flags (e.g. zero flag ZF, sign flag SF).

Instructions

• mov r1, r2: move r2 to r1
• add r1, r2: r1 + r2, the result will be stored in rax
• cmp r1, r2: r1 - r2, the result will be stored in ZF, SF flags
• jmp lbl: goto lbl
• je lbl: goto lbl if ZF=1
• jg lbl: goto lbl if SF=0
• jl lbl: goto lbl if SF=1
• syscall: make a syscall with the identifier stored in rax