Re: Using floating point calculations in kernel module (x86/amd64)

Even if by the nowadays standard ot seems strange, I suspect that you have no hard floating point support in you processor.
In fact __adddf3 and __muldf3 seem to be a soft implementation for floating point add and multiply support, while __floatunsidf is related to int to float conversions.
They are services provided at a very low level, possible at the compiler one.to emulate floating point 
RTAI has found a similar problem  in supporting complex math at the kernel level.
I solved it by  using what made available by LLVM.ORG, but the functions I needed rely on the availability of a hard FPU support for add/mul/div. A fact that may the matter far simpler.
Yours, instead, seem at the core of the basic FPU emulation, which is another matter.

Paolo
________________________________________
From: Rtai [[email protected]] on behalf of Paolo Mantegazza [[email protected]]
Sent: Thursday, August 11, 2016 11:03 AM
To: Wilfried Holzke; [email protected]
Subject: Re: [Rtai] Using floating point calculations in kernel module  (x86/amd64)

Does your CPU support floating point?
Have you configured RTAI for FP support in kernel space with NEWLIB-UCLIB-MUSL?
Can you run the test in "showroom/v3.x/kernel/math"?

Paolo
________________________________________
From: Rtai [[email protected]] on behalf of Wilfried Holzke [[email protected]]
Sent: Wednesday, August 10, 2016 7:15 PM
To: [email protected]
Subject: [Rtai] Using floating point calculations in kernel module      (x86/amd64)

Hi,

I am trying to build a module with floating point support, but I get the
following missing symbols:

__adddf3
__floatunsidf
__muldf3

In RTAI I found support for FP, but this is only for saving the state
bevor calling a procedure which uses FP(?). The procedure, in the module
I try to build, should be called from a RTAI Task or interrupt procedure.

Searching with google I found only old hints and examples for ARM CPUs.
Is there an example how to compile a module for x86/amd64 (flags for
gcc) or the kbuild makefiles
(https://www.kernel.org/doc/Documentation/kbuild/makefiles.txt)?

Thanks for any hints and help.

regards

   W. Holzke
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