RE: Macro expansion on MIPS

["Smets, Jan (Jan)" <jan dot smets at alcatel-lucent dot com>]

> -----Original Message-----
> From: Paul_Koning@Dell.com [mailto:Paul_Koning@Dell.com] 
> Sent: woensdag 5 oktober 2011 12:38
> To: Smets, Jan (Jan); binutils@sourceware.org
> Subject: RE: Macro expansion on MIPS
> 
> >>> Is there a way to disable macro expansion on MIPS? More 
> specific the 
> >>> replacement of 64bit instructions into two 32bit ones.
> >>> ...
> >> From: Paul_Koning@Dell.com [mailto:Paul_Koning@Dell.com]
> >> Have you considered O64?  It's like O32 except with 64 bit 
> registers 
> >> and 64-bit operations.  It gives you much of the benefits 
> you'd get 
> >> from N32 with a lot less effort.  We've used it for years with 
> >> excellent results.
> >
> >We have a very customized VxWorks 5 and a lot of in-house software.
> > It would be too much work to switch entirely to a new ABI in a few 
> >weeks/months. So I really want to get everything building 
> and running 
> >with the new toolchain. 64bit pointers are too much overhead for us, 
> >so we will likely go to N32 in the near future. But first 
> things first,
> > and that's a new toolchain. 
> 
> O64, in spite of its name, uses 32 bit pointers.  The best 
> way to understand it is "O32 with 64 bit registers".  So all 
> pointers remain the same, the register usage is the same 
> (four A registers for argument passing, for example), and 
> most importantly, the ABICALLS mechanism is the same as O32.
> 
> From past experience (working on millions of lines of code, 
> much of it custom), it is indeed possible to do this in a few 
> weeks.  It involves a few trivial changes to a small number 
> of assembly files, plus recompiling everything.  The main 
> effort is (a) building the O64 multilibs of the toolchain, 
> (b) testing.
> 
> And by the way, your code will then be faster and smaller.  
> All for probably less effort than manually fixing up 64 bit 
> assembly operations.
> 

Thanks for the clearification Paul. But I still think switching ABI is too much work right now and very risky. So I really want to continue to use O32 for now, and have minimal changes. I'm sure we will slowly transition away from it, but it will take some time.

Meanwhile I tried some things, please see my 'no brainer' examples:


as -mabi=32 -march=mips4     
  input: ld 
  output: lw + lw  


as -mabi=32 -march=mips4 
  input: .set mips64; ld        (or any ISA >= mips3)
  output: ld

Good, this is what I want! But it's almost impossible to find all the code that needs this fixup.


as -mabi=32 -march=mips64 
  input: ld 
  output: lw + lw 


 Why don't I get 'ld' as output? -march=mips64 != .set mips64 ?


as -mabi=32 -march=mips64 
  input: .set mips64; ld 
  output: ld


Does this indicate that there is something wrong with my assembler? 


- Jan