VFP vs. FPA for ARM?
Steven Scholz
steven.scholz@imc-berlin.de
Tue May 17 09:24:00 GMT 2005
Hi there,
a while back a had problems with with the byte order of doubles on an ARM9
system.
Nicolas Pitre wrote me:
>>Yes. On ARM, the two 32bit words of a double are themselves encoded
>>in native endian order, but the most significant word is always first.
>
> And for completeness, this is true only for FPA ordering. The new VFP
> ordering uses native memory ordering which is the same as i386 for litle
> endian, or ppc for big endian, as anyone would normally expect.
>
> The kernel FP emulators are emulating a FPA coprocessor though.
> When soft-float is used, it can be configured to use either FPA or VFP
> ordering.
Since I built my toolchain with crosstool using
KERNELCONFIG=`pwd`/arm.config
TARGET=arm-softfloat-linux-gnu
TARGET_CFLAGS="-O"
GCC_EXTRA_CONFIG="--with-float=soft"
GLIBC_EXTRA_CONFIG="--without-fp"
BINUTILS_DIR=binutils-2.15
GCC_DIR=gcc-3.3.3
GLIBC_DIR=glibc-2.3.3
LINUX_DIR=linux-2.6.10
I'd like to ask a few questions here:
1. "When soft-float is used" means the glibc, not the gcc !?
2. When I use soft-float then kernel FP emulator is not used !?
3. Which ordering is configured by crosstool?
4. How can I change that?
Thanks.
--
Steven
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