The code handling the pop76 opcode (ie. bnezc & jialc instructions) in
__compute_return_epc_for_insn() needs to set the value of $31 in the
jialc case, which is encoded with rs = 0. However its check to
differentiate bnezc (rs != 0) from jialc (rs = 0) was unfortunately
backwards, meaning that if we emulate a bnezc instruction we clobber $31
& if we emulate a jialc instruction it actually behaves like a jic
instruction.
Fix this by inverting the check of rs to match the way the instructions
are actually encoded.
Signed-off-by: Paul Burton <paul.burton@xxxxxxxxxx>
Fixes: 28d6f93d201d ("MIPS: Emulate the new MIPS R6 BNEZC and JIALC instructions")
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Cc: stable <stable@xxxxxxxxxxxxxxx> # v4.0+
---
arch/mips/kernel/branch.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index b11facd11c9d..f702a459a830 100644
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -804,8 +804,10 @@ int __compute_return_epc_for_insn(struct pt_regs *regs,
break;
}
/* Compact branch: BNEZC || JIALC */
- if (insn.i_format.rs)
+ if (!insn.i_format.rs) {
+ /* JIALC: set $31/ra */
regs->regs[31] = epc + 4;
+ }
regs->cp0_epc += 8;
break;
#endif
--
2.13.0
