gasm-sdk/asm/operand.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

package asm

// Operand is an instruction operand: a Reg, a Mem reference or an Imm value.
type Operand interface {
	isOperand()
}

// Imm is an immediate value.  Its encoded width is chosen by the instruction
// (sign-extended imm8 where possible, otherwise imm32, imm64 for MOV).
type Imm int64

func (Imm) isOperand() {}

// Mem is a memory operand of the form disp(base)(index*scale).
type Mem struct {
	Base     Reg
	Index    Reg
	Scale    int // 1, 2, 4 or 8; 0 means no index
	Disp     int64
	Size     int // operand width in bytes
	HasBase  bool
	HasIndex bool
}

func (Mem) isOperand() {}

// Ptr builds a plain displaced memory operand (base)+disp of the given size.
func Ptr(base Reg, disp int64, size int) Mem {
	return Mem{Base: base, Disp: disp, Size: size, HasBase: true}
}

// Idx builds an indexed memory operand disp(base)(index*scale).
func Idx(base, index Reg, scale int, disp int64, size int) Mem {
	return Mem{Base: base, Index: index, Scale: scale, Disp: disp, Size: size, HasBase: true, HasIndex: true}
}

// Rip builds a RIP-relative memory operand (RIP)+disp.
func Rip(disp int64, size int) Mem {
	return Mem{Disp: disp, Size: size}
}

// sbMem is a memory operand that references a static (SB) symbol.  It encodes
// as a RIP-relative reference with a placeholder displacement; the encoder
// records a patch site so the file-level layout can fill in the true rel32
// once the symbol's address is known.
type sbMem struct {
	size   int
	name   string // static symbol name (the GLOBL identifier)
	addend int64  // byte offset within the symbol
}

func (sbMem) isOperand() {}