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Allow rA=0 for 601 integer store-update instructions #236

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Merged
dingusdev merged 2 commits into from
Oct 10, 2026
Merged

Allow rA=0 for 601 integer store-update instructions #236

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c90a18e
ppc: allow rA=0 for 601 integer store-update instructions
mihaip Oct 9, 2026
63a3fdc
ppc: make illegal instructions more obvious
mihaip Oct 9, 2026
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11 changes: 11 additions & 0 deletions cpu/ppc/ppcexec.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -275,6 +275,17 @@ PPCOpcode* ppc_opcode_grabber = OpcodeGrabberNoFPU;
/** Exception helpers. */

void ppc_illegalop(uint32_t opcode) {
// Zero values are used as sentinels in the TNT ROM and are thus somewhat
// common, don't log them.
if (opcode) {
PPCDisasmContext ctx;
ctx.instr_code = opcode;
ctx.instr_addr = 0;
ctx.simplified = false;
auto op_name = disassemble_single(&ctx);
LOG_F(WARNING, "Illegal opcode exception raised for 0x%08x (decoded as %s). The PC was 0x%08x.", opcode, op_name.c_str(), ppc_state.pc);
}

ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
}

Expand Down
16 changes: 8 additions & 8 deletions cpu/ppc/ppcfpopcodes.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1025,7 +1025,7 @@ void dppc_interpreter::ppc_lfsu(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ea);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand All @@ -1046,7 +1046,7 @@ void dppc_interpreter::ppc_lfsux(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ea);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
return;
}
}
Expand All @@ -1070,7 +1070,7 @@ void dppc_interpreter::ppc_lfdu(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ea);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand All @@ -1091,7 +1091,7 @@ void dppc_interpreter::ppc_lfdux(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ea);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand All @@ -1114,7 +1114,7 @@ void dppc_interpreter::ppc_stfsu(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ea);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand All @@ -1135,7 +1135,7 @@ void dppc_interpreter::ppc_stfsux(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ea);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand All @@ -1156,7 +1156,7 @@ void dppc_interpreter::ppc_stfdu(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ea);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand All @@ -1175,7 +1175,7 @@ void dppc_interpreter::ppc_stfdux(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ea);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

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2 changes: 1 addition & 1 deletion cpu/ppc/ppcmmu.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1088,7 +1088,7 @@ static void mpc601_bat_update(uint32_t bat_reg)

static void mpc601_dbat_update(uint32_t /*bat_reg*/)
{
// ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
// ppc_illegalop(opcode);
}

static void ppc_ibat_update(uint32_t bat_reg)
Expand Down
44 changes: 24 additions & 20 deletions cpu/ppc/ppcopcodes.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1002,14 +1002,14 @@ void dppc_interpreter::ppc_mfspr(uint32_t opcode) {
switch (ref_spr) {
case SPR::MQ:
if (!(is_601 || include_601)) {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
return;
}
ppc_state.gpr[reg_d] = ppc_state.spr[ref_spr];
break;
case SPR::RTCL_U:
if (!is_601) {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
return;
}
calc_rtcl_value();
Expand All @@ -1019,7 +1019,7 @@ void dppc_interpreter::ppc_mfspr(uint32_t opcode) {
break;
case SPR::RTCU_U:
if (!is_601) {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
return;
}
calc_rtcl_value();
Expand All @@ -1029,7 +1029,7 @@ void dppc_interpreter::ppc_mfspr(uint32_t opcode) {
break;
case SPR::DEC_U:
if (!is_601) {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
return;
}
// fallthrough
Expand Down Expand Up @@ -1093,13 +1093,13 @@ void dppc_interpreter::ppc_mtspr(uint32_t opcode) {
if (is_601 || include_601)
ppc_state.spr[ref_spr] = val;
else
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
break;
case SPR::RTCL_U:
case SPR::RTCU_U:
case SPR::DEC_U:
if (!is_601) {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
break;
case SPR::XER:
Expand Down Expand Up @@ -1214,7 +1214,7 @@ void dppc_interpreter::ppc_mftb(uint32_t opcode) {
ppc_state.spr[TBL_S] = uint32_t(tbr_value);
break;
default:
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand Down Expand Up @@ -1700,14 +1700,16 @@ void dppc_interpreter::ppc_stu(uint32_t opcode) {
#endif
ppc_grab_regssa(opcode);

if (reg_a != 0) {
// MPC601 permits RA=0 for POWER compatibility and suppresses the update.
if (reg_a != 0 || is_601) {
uint32_t ea = int32_t(int16_t(opcode));
ea += ppc_result_a;
ea += reg_a ? ppc_result_a : 0;
mmu_write_vmem<T>(opcode, ea, ppc_result_d);
ppc_state.gpr[reg_a] = ea;
if (reg_a != 0)
ppc_state.gpr[reg_a] = ea;
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}

}
Expand All @@ -1723,13 +1725,15 @@ void dppc_interpreter::ppc_stux(uint32_t opcode) {
#endif
ppc_grab_regssab(opcode);

if (reg_a != 0) {
uint32_t ea = ppc_result_a + ppc_result_b;
// MPC601 permits RA=0 for POWER compatibility and suppresses the update.
if (reg_a != 0 || is_601) {
uint32_t ea = (reg_a ? ppc_result_a : 0) + ppc_result_b;
mmu_write_vmem<T>(opcode, ea, ppc_result_d);
ppc_state.gpr[reg_a] = ea;
if (reg_a != 0)
ppc_state.gpr[reg_a] = ea;
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand Down Expand Up @@ -1821,7 +1825,7 @@ void dppc_interpreter::ppc_lzu(uint32_t opcode) {
ppc_result_a = ea;
ppc_store_iresult_reg(reg_a, ppc_result_a);
} else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand Down Expand Up @@ -1857,7 +1861,7 @@ void dppc_interpreter::ppc_lzux(uint32_t opcode) {
ppc_result_a = ea;
ppc_store_iresult_reg(reg_a, ppc_result_a);
} else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand Down Expand Up @@ -1889,7 +1893,7 @@ void dppc_interpreter::ppc_lhau(uint32_t opcode) {
ppc_result_a = ea;
ppc_store_iresult_reg(reg_a, ppc_result_a);
} else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand All @@ -1906,7 +1910,7 @@ void dppc_interpreter::ppc_lhaux(uint32_t opcode) {
ppc_store_iresult_reg(reg_a, ppc_result_a);
}
else {
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
}

Expand Down Expand Up @@ -2014,7 +2018,7 @@ void dppc_interpreter::ppc_lswx(uint32_t opcode) {
if ((reg_d == 0 && reg_a == 0) || (reg_d == reg_a) || (reg_d == reg_b)) {
// UNTESTED! Does invalid form really cause exception?
// G4 doesn't do exception
ppc_exception_handler(Except_Type::EXC_PROGRAM, Exc_Cause::ILLEGAL_OP);
ppc_illegalop(opcode);
}
*/

Expand Down
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