Re: mips fp/s8 usage in objdump

[cgd at broadcom dot com]

At Sun, 30 Mar 2003 23:10:15 +0000 (UTC), "J. Grant" wrote:
> Due to the differing use of fp/s8 is there a reason s8 was selected as
> default? In my experience s8 has been used as fp.

To quote various documents i have laying about:

The MIPS SysV psABI supplement (p 3-12) says:

$30	s8	saved register (like s0-s7).


See MIPS Run (p.23) says:

30	s8/fp	Ninth register variable; subroutines that need one can
		use this as a frame pointer.


Finally, not that they're really relevant, the n32 ABI Handbook
(specifically, the page at
http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi/srch3 at n32/0650/bks/SGI_Developer/books/Mpro_n32_ABI/sgi_html/ch02.html#IT02.calling-26
8-) say about that register on n32 / n64 (not that they're really
relevant to o32):

$30	s8	Frame pointer (if needed)	Callee-saved.


In other words, in my opinion:

* "fp" will occasionally be correct.  "s8" is always correct.

and,

* Even in documents that acknowledge that this register is sometimes
  used as a frame pointer describe it as "s8"...



> I think
> there might be a MIPS ABI name for fp usage, but can't remember the name.

AFAICT, there is and it's "s8."  8-)



cgd
-- 
Chris Demetriou                                            Broadcom Corporation
Principal Design Engineer                     Broadband Processor Business Unit
  Any opinions expressed in this message are mine, not necessarily Broadcom's.