Re: [RFC PATCH 32/42] docker: Add gentoo-mipsr5900el-cross image

[Maciej W. Rozycki]

On Fri, 12 Mar 2021, Philippe Mathieu-Daudé wrote:

> > but your two options to 
> > choose from are:
> > 
> > 1. Build for the soft-float ABI (`-msoft-float') where any FP calculations 
> >    are compiled such as to be made by the CPU using integer arithmetic.
> 
> With the Debian toolchain I get:
> 
> /usr/include/stdio.h:27:10: fatal error: bits/libc-header-start.h: No
> such file or directory
>  #include <bits/libc-header-start.h>
>           ^~~~~~~~~~~~~~~~~~~~~~~~~~

 You need to have a soft-float multilib available.  You can use:

$ gcc -print-multi-lib

to see what multilibs are available.  You'd have to have one that includes 
`-msoft-float' and `-mabi=n32' both at a time.  If there's no such one, 
then you'll have to build your own cross-compiler (including soft-float 
libc).

> > 2. Build for a generic MIPS ISA, for the R5900/n32 that would be MIPS III
> >    (`-march=mips3'), and rely on the kernel FPU emulation.
> 
> Shouldn't -march=r5900 imply -march=mips3?

 It does:

MIPS_CPU ("r5900", PROCESSOR_R5900, 3, 0)

however it is a distinct architecture owing to the differences from plain 
MIPS III ISA, and obviously the compiler and the assembler both know that.

  Maciej