Function readOpcodeRegister

arch/X86/X86DisassemblerDecoder.c:1741–1776

* readOpcodeRegister - Reads an operand from the opcode field of an * instruction and interprets it appropriately given the operand width. * Handles AddRegFrm instructions. * * @param insn - the instruction whose opcode field is to be read. * @param size - The width (in bytes) of the register being specified. * 1 means AL and friends, 2 means AX, 4 means EAX, and 8 means

 * @return      - 0 on success; nonzero otherwise.
 */
static int readOpcodeRegister(struct InternalInstruction* insn, uint8_t size)
{
	if (size == 0)
		size = insn->registerSize;

	switch (size) {
		case 1:
			insn->opcodeRegister = (Reg)(MODRM_REG_AL + ((bFromREX(insn->rexPrefix) << 3)
						| (insn->opcode & 7)));
			if (insn->rexPrefix &&
					insn->opcodeRegister >= MODRM_REG_AL + 0x4 &&
					insn->opcodeRegister < MODRM_REG_AL + 0x8) {
				insn->opcodeRegister = (Reg)(MODRM_REG_SPL
						+ (insn->opcodeRegister - MODRM_REG_AL - 4));
			}

			break;
		case 2:
			insn->opcodeRegister = (Reg)(MODRM_REG_AX
					+ ((bFromREX(insn->rexPrefix) << 3)
						| (insn->opcode & 7)));
			break;
		case 4:
			insn->opcodeRegister = (Reg)(MODRM_REG_EAX
					+ ((bFromREX(insn->rexPrefix) << 3)
						| (insn->opcode & 7)));
			break;
		case 8:
			insn->opcodeRegister = (Reg)(MODRM_REG_RAX
					+ ((bFromREX(insn->rexPrefix) << 3)
						| (insn->opcode & 7)));
			break;
	}

	return 0;
}

/*
 * readImmediate - Consumes an immediate operand from an instruction, given the