From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264503AbUEaCFq (ORCPT ); Sun, 30 May 2004 22:05:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264505AbUEaCFq (ORCPT ); Sun, 30 May 2004 22:05:46 -0400 Received: from mailout.despammed.com ([65.112.71.29]:46583 "EHLO mailout.despammed.com") by vger.kernel.org with ESMTP id S264503AbUEaCFi (ORCPT ); Sun, 30 May 2004 22:05:38 -0400 Date: Sun, 30 May 2004 20:52:23 -0500 (CDT) Message-Id: <200405310152.i4V1qNk03732@mailout.despammed.com> From: ndiamond@despammed.com To: linux-kernel@vger.kernel.org Subject: How to use floating point in a module? X-Mailer: despammed.com Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: 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?