How to use floating point in a module?

ndiamond_at_despammed.com
Date: 05/31/04

  • Next message: Måns Rullgård: "Re: How to use floating point in a module?" 
    Date:	Sun, 30 May 2004 20:52:23 -0500 (CDT)
To: linux-kernel@vger.kernel.org

    A driver, implemented as a module, must do some floating-point computations including trig functions. Fortunately the architecture is x86. A few hundred kilograms of searching (almost a ton of searching :-) seems to reveal the following possibilities.

    Recompile GNU's libc with option "--without-fp". If I understand correctly, the resulting libc will completely avoid using floating-point hardware while providing floating-point computations to its client. Do I understand correctly?

    Compile the module's .c files with gcc's "-msoft-float" option and "-D__NO_MATH_INLINES". (Actually I think "-D__NO_MATH_INLINES" is probably unnecessary here.)

    Link the module's .o files with the version of libc produced above, and try to get a loadable .ko from this... or a loadable .o since the target is still kernel 2.4.something.

    But I'm sure there must be a ton of pitfalls that I'm not seeing here. I'm not the first poor slob who got tasked with shoving some floating-point into a module. My searches found a few tricks that people used for a few floating-point operations, but they used the real floating-point hardware and they didn't really reveal all the trickery they used. (Not that I can blame them, since the hackery they did must be virtually unteachable.) I didn't find anyone saying that they found a safe method of doing it, whether or not a safe method might somewhat resemble the ideas I've just presented. I didn't find anyone saying they got trig functions into it either. If my ideas could possibly work, surely they would have been done already. So, what am I missing?

    And does anyone know a really safe method?
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  • Next message: Måns Rullgård: "Re: How to use floating point in a module?"

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