Re: Building newlib without -mhard-float

[Dave Murphy <wintermute2k4 at ntlworld dot com>]

Rick Mann wrote:
> I'm having a heck of a time getting newlib variants for ARM with VFP 
> instructions. I configure using --with-float=soft, but it still builds 
> a bunch of versions using -mhard-float. I tried modifying 
> CFLAGS_FOR_TARGET to include -mcpu=xscale and/or -march=armv5te, but 
> then I get errors about it confilicting with -mhard-float.

I've been maintaining a gcc/newlib based arm cross compiler for a few 
years now and in the beginning I experienced a lot of trouble with soft 
vs hard float library issues. After a lot of searching and testing I 
found that an arm-elf compiler produces soft-float binaries by default 
but that the object files are actually marked as hard-float which, as 
far as I could determine, is a legacy thing related to systems which 
used FPU emulation. The only way I could get my toolchain to function as 
intended was to use the default options and *not* use -msoft-float at 
*any* point anywhere in the build process.

Most recently I had problems with a system which contains dual 
processors, one arm7tdmi and one arm946e-s. The arm-elf toolchain 
complained loudly about VFP mismatches when I tried to build code for 
armv5te but obviously I wanted the libraries to be built for armv4t so 
that the toolchain could still build binaries for the other supported 
platforms. I asked for advice on IRC from Richard Earnshaw and some of 
the other developers working with ARM and they advised me to switch to 
arm-eabi which allows code for armv4t and armv5te to be mixed freely 
without all the mismatching problems. It also allows for arm and thumb 
code to co-exist without the need for the interworking libraries needed 
with arm-elf. I've had very few problems since switching over.

The toolchain I'm maintaining is biased towards amateur game development 
but is still useful as a more general ARM toolchain. The main site is at 
http://www.devkitpro.org, all the buildscripts and patches I use are in 
CVS at http://sourceforge.net/projects/devkitpro

My newlib patches are heavily modified to add a pseudo device API which 
handles the low level stdio functions so you're probably better off 
sticking with vanilla newlib and just using the buildscripts for general 
guidance.

Dave