EABI_32BIT_DUMMY_ARG is not expected in the following function, the EncodedJSValue parameter is already aligned to even registers for MIPS and ARM EABI (in 3rd and 4th argument registers): ALWAYS_INLINE MacroAssembler::Call JIT::callOperation(J_JITOperation_EAapJ operation, int dst, ArrayAllocationProfile* arg1, GPRReg arg2Tag, GPRReg arg2Payload) { setupArgumentsWithExecState(TrustedImmPtr(arg1), EABI_32BIT_DUMMY_ARG arg2Payload, arg2Tag); return appendCallWithExceptionCheckSetJSValueResult(operation, dst); }