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() {}

// RegList is a bracketed register range, [Z0-Z3]: the four-register source
// of the 4FMAPS and 4VNNIW families.  The EVEX emit path carries the list's
// low register through the inverted 5-bit V'VVVV field; the three higher
// registers are implied by the instruction, so only the pair travels here.
type RegList struct {
	Lo Reg
	Hi Reg // implied by the encoding; Lo.idx+3 by construction
}

func (RegList) isOperand() {}

// FloatImm is a floating-point immediate ($-1.0).  The SSE mnemonics whose
// encoding takes an XMM/memory source at that position rewrite it as a read
// from a read-only pool constant ($f64.<hex> or $f32.<hex>), the toolchain's
// own behaviour; every other instruction rejects it.
type FloatImm struct {
	Text string // the numeric text as written, sign excluded
	Neg  bool   // a leading minus
}

func (FloatImm) 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}
}

// 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() {}

// isX86Mem reports whether the operand is an amd64 memory reference: a base
// or indexed Mem, or an SB-relative sbMem.  Encoders that gate on "memory in
// this position" must accept both; the r/m emitters distinguish the two
// themselves.
func isX86Mem(o Operand) bool {
	switch o.(type) {
	case Mem, sbMem:
		return true
	default:
		return false
	}
}