static int kvm_compute_return_epc()

in kvm/emulate.c [40:241]

• 166 lines of code
• 49 McCabe index (conditional complexity)

static int kvm_compute_return_epc(struct kvm_vcpu *vcpu, unsigned long instpc,
				  unsigned long *out)
{
	unsigned int dspcontrol;
	union mips_instruction insn;
	struct kvm_vcpu_arch *arch = &vcpu->arch;
	long epc = instpc;
	long nextpc;
	int err;

	if (epc & 3) {
		kvm_err("%s: unaligned epc\n", __func__);
		return -EINVAL;
	}

	/* Read the instruction */
	err = kvm_get_badinstrp((u32 *)epc, vcpu, &insn.word);
	if (err)
		return err;

	switch (insn.i_format.opcode) {
		/* jr and jalr are in r_format format. */
	case spec_op:
		switch (insn.r_format.func) {
		case jalr_op:
			arch->gprs[insn.r_format.rd] = epc + 8;
			fallthrough;
		case jr_op:
			nextpc = arch->gprs[insn.r_format.rs];
			break;
		default:
			return -EINVAL;
		}
		break;

		/*
		 * This group contains:
		 * bltz_op, bgez_op, bltzl_op, bgezl_op,
		 * bltzal_op, bgezal_op, bltzall_op, bgezall_op.
		 */
	case bcond_op:
		switch (insn.i_format.rt) {
		case bltz_op:
		case bltzl_op:
			if ((long)arch->gprs[insn.i_format.rs] < 0)
				epc = epc + 4 + (insn.i_format.simmediate << 2);
			else
				epc += 8;
			nextpc = epc;
			break;

		case bgez_op:
		case bgezl_op:
			if ((long)arch->gprs[insn.i_format.rs] >= 0)
				epc = epc + 4 + (insn.i_format.simmediate << 2);
			else
				epc += 8;
			nextpc = epc;
			break;

		case bltzal_op:
		case bltzall_op:
			arch->gprs[31] = epc + 8;
			if ((long)arch->gprs[insn.i_format.rs] < 0)
				epc = epc + 4 + (insn.i_format.simmediate << 2);
			else
				epc += 8;
			nextpc = epc;
			break;

		case bgezal_op:
		case bgezall_op:
			arch->gprs[31] = epc + 8;
			if ((long)arch->gprs[insn.i_format.rs] >= 0)
				epc = epc + 4 + (insn.i_format.simmediate << 2);
			else
				epc += 8;
			nextpc = epc;
			break;
		case bposge32_op:
			if (!cpu_has_dsp) {
				kvm_err("%s: DSP branch but not DSP ASE\n",
					__func__);
				return -EINVAL;
			}

			dspcontrol = rddsp(0x01);

			if (dspcontrol >= 32)
				epc = epc + 4 + (insn.i_format.simmediate << 2);
			else
				epc += 8;
			nextpc = epc;
			break;
		default:
			return -EINVAL;
		}
		break;

		/* These are unconditional and in j_format. */
	case jal_op:
		arch->gprs[31] = instpc + 8;
		fallthrough;
	case j_op:
		epc += 4;
		epc >>= 28;
		epc <<= 28;
		epc |= (insn.j_format.target << 2);
		nextpc = epc;
		break;

		/* These are conditional and in i_format. */
	case beq_op:
	case beql_op:
		if (arch->gprs[insn.i_format.rs] ==
		    arch->gprs[insn.i_format.rt])
			epc = epc + 4 + (insn.i_format.simmediate << 2);
		else
			epc += 8;
		nextpc = epc;
		break;

	case bne_op:
	case bnel_op:
		if (arch->gprs[insn.i_format.rs] !=
		    arch->gprs[insn.i_format.rt])
			epc = epc + 4 + (insn.i_format.simmediate << 2);
		else
			epc += 8;
		nextpc = epc;
		break;

	case blez_op:	/* POP06 */
#ifndef CONFIG_CPU_MIPSR6
	case blezl_op:	/* removed in R6 */
#endif
		if (insn.i_format.rt != 0)
			goto compact_branch;
		if ((long)arch->gprs[insn.i_format.rs] <= 0)
			epc = epc + 4 + (insn.i_format.simmediate << 2);
		else
			epc += 8;
		nextpc = epc;
		break;

	case bgtz_op:	/* POP07 */
#ifndef CONFIG_CPU_MIPSR6
	case bgtzl_op:	/* removed in R6 */
#endif
		if (insn.i_format.rt != 0)
			goto compact_branch;
		if ((long)arch->gprs[insn.i_format.rs] > 0)
			epc = epc + 4 + (insn.i_format.simmediate << 2);
		else
			epc += 8;
		nextpc = epc;
		break;

		/* And now the FPA/cp1 branch instructions. */
	case cop1_op:
		kvm_err("%s: unsupported cop1_op\n", __func__);
		return -EINVAL;

#ifdef CONFIG_CPU_MIPSR6
	/* R6 added the following compact branches with forbidden slots */
	case blezl_op:	/* POP26 */
	case bgtzl_op:	/* POP27 */
		/* only rt == 0 isn't compact branch */
		if (insn.i_format.rt != 0)
			goto compact_branch;
		return -EINVAL;
	case pop10_op:
	case pop30_op:
		/* only rs == rt == 0 is reserved, rest are compact branches */
		if (insn.i_format.rs != 0 || insn.i_format.rt != 0)
			goto compact_branch;
		return -EINVAL;
	case pop66_op:
	case pop76_op:
		/* only rs == 0 isn't compact branch */
		if (insn.i_format.rs != 0)
			goto compact_branch;
		return -EINVAL;
compact_branch:
		/*
		 * If we've hit an exception on the forbidden slot, then
		 * the branch must not have been taken.
		 */
		epc += 8;
		nextpc = epc;
		break;
#else
compact_branch:
		/* Fall through - Compact branches not supported before R6 */
#endif
	default:
		return -EINVAL;
	}

	*out = nextpc;
	return 0;
}