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 f9cb13c..a1fd878 100644
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -399,6 +399,16 @@
* @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 @@
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);