1 files changed, 31 insertions, 0 deletions

diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index f9cb13c56595..a1fd8786d716 100644
--- 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);