JR opcode (Jump Register) only takes 1 argument, $rs.
JALR (Jump And Link Register) takes 3: $rs, $rd and $hint.
Commit 6af0bf9c7c3 added their processing into decode_opc() as:
case 0x08 ... 0x09: /* Jumps */
gen_compute_branch(ctx, op1 | EXT_SPECIAL, rs, rd, sa);
having both opcodes handled in the same function: gen_compute_branch.
Per JR encoding, both $rd and $hint ('sa') are decoded as zero.
Later this code got extracted to decode_opc_special(),
commit 7a387fffce5 used definitions instead of magic values:
case OPC_JR ... OPC_JALR:
gen_compute_branch(ctx, op1, rs, rd, sa);
Finally commit 0aefa33318b moved OPC_JR out of decode_opc_special,
to a new 'decode_opc_special_legacy' function:
@@ -15851,6 +15851,9 @@ static void decode_opc_special_legacy(CPUMIPSState
*env, DisasContext *ctx)
+ case OPC_JR:
+ gen_compute_branch(ctx, op1, 4, rs, rd, sa);
+ break;
@@ -15933,7 +15936,7 @@ static void decode_opc_special(CPUMIPSState *env,
DisasContext *ctx)
- case OPC_JR ... OPC_JALR:
+ case OPC_JALR:
gen_compute_branch(ctx, op1, 4, rs, rd, sa);
break;
Since JR is now handled individually, it is pointless to decode
and pass it unused arguments. Replace them by simple zero value
to avoid confusion with this opcode.
Signed-off-by: Philippe Mathieu-Daudé <f4...@amsat.org>
---
target/mips/tcg/translate.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/target/mips/tcg/translate.c b/target/mips/tcg/translate.c
index 5b03545f099..bf71724f3f0 100644
--- a/target/mips/tcg/translate.c
+++ b/target/mips/tcg/translate.c
@@ -14203,7 +14203,7 @@ static void decode_opc_special_legacy(CPUMIPSState
*env, DisasContext *ctx)
break;
#endif
case OPC_JR:
- gen_compute_branch(ctx, op1, 4, rs, rd, sa, 4);
+ gen_compute_branch(ctx, op1, 4, rs, 0, 0, 4);
break;
case OPC_SPIM:
#ifdef MIPS_STRICT_STANDARD
--
2.31.1
