Using ARM/Neon fp hardware with libc

robjsstewart at ...196... robjsstewart at ...196...
Fri Oct 2 22:24:11 CEST 2015

It's a bit more complicated than just setting the correct compiler options in  Compiling the various math functions for hardfp works ok as you would expect. The issue comes when building the .so library. The linker call is set to merge the software fp version of libgcc.a. I'm having trouble following the library build process to determine where I can change to using .../fpu/libgcc.a.

Any hints would be appreciated.


Sent from my android device.

-----Original Message-----
From: Christian Helmuth <christian.helmuth at ...1...>
To: genode-main at
Sent: Thu, 01 Oct 2015 5:10 AM
Subject: Re: Using ARM/Neon fp hardware with libc

Hello Bob,

On Wed, Sep 30, 2015 at 03:14:26PM -0400, robjsstewart at ...9... wrote:
> I'm exploring compiling a couple of targets in my Genode, base-hw
> system to use the hardware fp in the Neon coprocessor on an ARM
> Cortex A8 SOC, to get some performance improvement. I can add the
> CC_OPT line containing -mfloat-abi=hard and -mfu=neon-vfpv4 to
> appropreate That should result in the Neon fp unit being
> called to perform the calculations. If I want use libc math
> functions I assume I must recompile libc with the same compile
> options added. Are there build variables that allow me to do that to
> the libc library? 

With 15.02, you may try to patch repos/libports/lib/mk/arm/
accordingly. There is not way to just "configure" compilation options
for libc that I know of.

Christian Helmuth
Genode Labs · · /ˈdʒiː.nəʊd/

Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth

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