Problem with printf and float

[Jeppe Ledet-Pedersen <jledet at space dot aau dot dk>]

Hi everybody,

This question was originally posted on the crossgcc mailing list, but my 
problem appears to be related to Newlib so I'll repost it here. My 
original question can be found at 
http://sourceware.org/ml/crossgcc/2010-10/msg00147.html

I have successfully compiled a toolchain for my arm7tdmi with 
crosstool-NG. I use GCC 4.5.1, Newlib CVS and Binutils 2.20.1. I have 
enabled the EABI and software floating point.

I can compile my codebase with no errors or warnings, but I am having 
trouble when trying to use printf and siblings with floating point 
values. The problem seems to stem from a mismatch between VFP and FPA 
floating point formats.

With my test code (http://pastebin.com/3Dsb9siL), I get the following 
output:

00 00 00 00 00 00 55 c0
a is 0.000000
00 00 55 c0 00 00 00 00
a (flipped) is -84.000000

So it appears that GCC stores the double value in correct little-endian, 
VFP format but Newlib will only print it if converted to FPA format. I 
have looked through the code for _vfprint_r and _dtoa_r but haven't 
noticed anything suspicious. As far as I can see, everything seems correct.

If I i run "arm-unknown-eabi-cpp -dD" my toolchain defines both 
__ARMEL__, __SOFTFP__ and __VFP_FP__ which should be taken into account 
by Newlib in include/machine/ieeefp.h to use the correct pure little 
endian floating point format.

Any advice on what could cause this behavior? If you need additional 
information, just let me know.

You can see my full crosstool-NG build log at 
http://kom.aau.dk/~jledet/build_vfp.log.bz2

Thank you in advance.

Best regards,
Jeppe