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Date: Fri, 13 Jul 2012 10:15:25 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: mips port working! & remaining issues

* Rich Felker <dalias@...ifal.cx> [2012-07-13 01:23:13 -0400]:
> Another major omission shared with arm is that setjmp/longjmp cannot
> preserve floating point registers. This is because I don't yet know
> how to determine at runtime whether hard-float is available, and the
> registers can't be saved unless they can be determined to exist. Help
> solving this problem would also be appreciated.
> 

then use compile time check:
if libc is compiled with -msoft-float then dont save the registers
otherwise save them

i guess gcc has some predefined macro so you can check soft float
at compile time

when gcc compiles with hard float for mips there will be a
a .gnu.attributes section in the object file which is dumped
by readelf as
  Tag_GNU_MIPS_ABI_FP: Hard float (-mdouble-float)
and binutils ld warns when such .o is linked with a soft-float .o

so i think we shouldn't worry about applications using hard float
while the libc is soft float

as for runtime check
on mips you may grep for '^  FPU' in /proc/cpuinfo
on arm '^Features' tells the fpu variant
but i guess these are not very robust
http://git.kernel.org/?p=linux/kernel/git/stable/linux-stable.git;a=blob;f=arch/mips/kernel/proc.c
http://git.kernel.org/?p=linux/kernel/git/stable/linux-stable.git;a=blob;f=arch/arm/kernel/setup.c

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