Re: [PATCH 3/4] default-configs: Support o32 ABI with 64-bit MIPS CPUs

[Maciej W. Rozycki]

On Thu, 19 Nov 2020, Philippe Mathieu-Daudé wrote:

> MIPS o32 ABI on 64-bit CPUs looks like a ILP32-on-64bit data
> model, allowing 64-bit arithmetic and data movement instructions.
> 
> This is the default ABI used by the "Sony Linux Toolkit for
> Playstation 2".

 Please don't, not at least with a generic configuration (i.e. make it 
unambiguous that this is R5900-specific).  This only works with R5900 
because it does not implement the MIPS ISA correctly (e.g. see what $ra is 
set to with JAL/JALR/etc. in the kernel mode), and it is not supported by 
the standard Linux ABI.  Use n32 instead, which has the same functionality 
and is standard (and is also a better ABI in terms of performance).

 You'd probably need to implement all the R5900 addressing quirks for your 
proposed hack to match hardware, or otherwise you'll end up with emulation 
that creates its own reality.

  Maciej