Eric Fisher <[EMAIL PROTECTED]> writes: > I'd like to know why mips doesn't define $30 and $31 as fix registers? > And when should they be defined true?
Neither register has a use which is fixed by either the hardware or the ABI. $30 is generally the frame pointer, but gcc will only use a frame pointer which it is required to. When a function does not need a frame pointer, $30 is available as a caller-saved register. $31 is used by hardware in a jal instruction, and the ABI requires its used in a jalr instruction. However, in code that does not make a function call, it is perfectly reasonable for gcc to use $31 as a general caller-saved register, assuming of course that gcc has saved the address to which the function should return. Ian
