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: Markos Chandras <markos.chandras@imgtec.com>

diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index f9cb13c5659574e08e0a56b985f628116cdb05d5..a1fd8786d716fa6ad48a8e1fc62b015e32a17386 100644 (file)
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -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);

diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index 798204e492fc7c83fe7b5b49fc9212483a603caf..c770617dc34024914fa535c0b632a73657c67366 100644 (file)
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -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 +