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Commit a8ff66f5 authored by Markos Chandras's avatar Markos Chandras
Browse files

MIPS: Emulate the new MIPS R6 B{L,G}Ε{Z,}{AL,}C instructions 



MIPS R6 added the following four instructions which share the
BLEZ and BLEZL opcodes:

BLEZALC: Compact branch-and-link if GPR rt is <= to zero
BGEZALC: Compact branch-and-link if GPR rt is >= to zero
BLEZC  : Compact branch if GPR rt is <= to zero
BGEZC  : Compact branch if GPR rt is >= to zero
BGEC   : Compact branch if GPR rs is less than or equal to GPR rt
BGEUC  : Similar to BGEC but unsigned.

Signed-off-by: default avatarMarkos Chandras <markos.chandras@imgtec.com>
parent c8a34581

arch/mips/kernel/branch.c

+31 −0
Original line number Diff line number Diff line
@@ -399,6 +399,16 @@ int __MIPS16e_compute_return_epc(struct pt_regs *regs) 
 * @returns:	-EFAULT on error and forces SIGBUS, and on success

 *		returns 0 or BRANCH_LIKELY_TAKEN as appropriate after

 *		evaluating the branch.

 *

 * MIPS R6 Compact branches and forbidden slots:

 *	Compact branches do not throw exceptions because they do

 *	not have delay slots. The forbidden slot instruction ($PC+4)

 *	is only executed if the branch was not taken. Otherwise the

 *	forbidden slot is skipped entirely. This means that the

 *	only possible reason to be here because of a MIPS R6 compact

 *	branch instruction is that the forbidden slot has thrown one.

 *	In that case the branch was not taken, so the EPC can be safely

 *	set to EPC + 8.

 */

int __compute_return_epc_for_insn(struct pt_regs *regs,

				   union mips_instruction insn)
@@ -590,6 +600,27 @@ int __compute_return_epc_for_insn(struct pt_regs *regs, 
		if (NO_R6EMU)

			goto sigill_r6;

	case blez_op:

		/*

		 * Compact branches for R6 for the

		 * blez and blezl opcodes.

		 * BLEZ  | rs = 0 | rt != 0  == BLEZALC

		 * BLEZ  | rs = rt != 0      == BGEZALC

		 * BLEZ  | rs != 0 | rt != 0 == BGEUC

		 * BLEZL | rs = 0 | rt != 0  == BLEZC

		 * BLEZL | rs = rt != 0      == BGEZC

		 * BLEZL | rs != 0 | rt != 0 == BGEC

		 *

		 * For real BLEZ{,L}, rt is always 0.

		 */



		if (cpu_has_mips_r6 && insn.i_format.rt) {

			if ((insn.i_format.opcode == blez_op) &&

			    ((!insn.i_format.rs && insn.i_format.rt) ||

			     (insn.i_format.rs == insn.i_format.rt)))

				regs->regs[31] = epc + 4;

			regs->cp0_epc += 8;

			break;

		}

		/* rt field assumed to be zero */

		if ((long)regs->regs[insn.i_format.rs] <= 0) {

			epc = epc + 4 + (insn.i_format.simmediate << 2);

arch/mips/math-emu/cp1emu.c

+24 −0
Original line number Diff line number Diff line
@@ -552,6 +552,30 @@ static int isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn, 
		if (NO_R6EMU)

			break;

	case blez_op:



		/*

		 * Compact branches for R6 for the

		 * blez and blezl opcodes.

		 * BLEZ  | rs = 0 | rt != 0  == BLEZALC

		 * BLEZ  | rs = rt != 0      == BGEZALC

		 * BLEZ  | rs != 0 | rt != 0 == BGEUC

		 * BLEZL | rs = 0 | rt != 0  == BLEZC

		 * BLEZL | rs = rt != 0      == BGEZC

		 * BLEZL | rs != 0 | rt != 0 == BGEC

		 *

		 * For real BLEZ{,L}, rt is always 0.

		 */

		if (cpu_has_mips_r6 && insn.i_format.rt) {

			if ((insn.i_format.opcode == blez_op) &&

			    ((!insn.i_format.rs && insn.i_format.rt) ||

			     (insn.i_format.rs == insn.i_format.rt)))

				regs->regs[31] = regs->cp0_epc +

					dec_insn.pc_inc;

			*contpc = regs->cp0_epc + dec_insn.pc_inc +

				dec_insn.next_pc_inc;



			return 1;

		}

		if ((long)regs->regs[insn.i_format.rs] <= 0)

			*contpc = regs->cp0_epc +

				dec_insn.pc_inc +