JR opcode (Jump Register) only takes 1 argument, $rs.
JALR (Jump And Link Register) takes 3: $rs, $rd and $hint.
Commit 6af0bf9c7c 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 7a387fffce used definitions instead of magic values:
case OPC_JR ... OPC_JALR:
gen_compute_branch(ctx, op1, rs, rd, sa);
Finally commit 0aefa33318 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 <f4bug@amsat.org>
Message-Id: <20210730225507.2642827-1-f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
c8b69a2a92