Re: multilib won't build soft-float libraries for strongarm-elf

[Richard Earnshaw <rearnsha at arm dot com>]

> For some reason when I build a gcc cross for strongarm-elf using a cygwin
> host I don't get the soft floating point libraries.  I don't get any errors
> while building, and the croos compiler works fine, just no soft-float
> libraries.
> 
> Multilib appears to be working as I get be (-mbig-endian) and fpu
> (-mhard-float) directories populated with libraries.  I thought the default
> library might be soft-float/little-endian but when I compile a c or c++ app
> and then try and link it I get an error telling me that the library was
> compiled for hardware FP.
> 
> Can anyone help me - I've read everything and tried everything I can but
> just can't seem to get the expected results.  I hope the following
> information will help.
> 

Because of the way the compiler passes directives to the assembler and the 
way that the linker checks for flags we have the situation where code 
compiled with a compiler whose default configuration is to produce 
soft-float code is marked as incompatible with code that is compiled with 
the -msoft-float flag.  This is really a bug in gcc... (but fixing it 
would leave a nasty backwards-compatibility problem for binary linking).

You need to check the way your compiler is configured.  Compile the 
following to assembly and check the output:

double f()
{
  return 1.0;
}

If the compiler puts the result into f0, then your configuration is using 
hard-float.  If it puts the result in r0,r1 then you have a soft-float 
compiler by default.

For the second scenario, the best thing to do is to always use the 
compiler *without* the soft-float flag and just accept it.  For the former 
case things are a bit more complex if you aren't getting those soft-float 
multilibs that you want (if you are, then you can just use -msoft-float 
all the time, including during linking and things should just work).

My understanding from a quick glance at the sources is that the 
strongarm-elf configuration does default to soft-float, so there is no 
need ever to specify -msoft-float on the command line; I think that would 
be your best approach.

R.


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