Question on including 'math.h' from C runtime...

Question on including 'math.h' from C runtime...

[Steven J. Hill]

Greetings.

I checked in the archives and did not see a discussion of this
anywhere. I have received some Linux kernel code from a project
that I have inherited and a couple of the drivers are including
math.h from the C library. This being the header file from
'/usr/include/math.h' in most cases. There are only two places
in the kernel that also include this header file. They are:

   drivers/atm/iphase.c
   drivers/net/hamradio/soundmodem/gentbl.c

As far as I can tell '/usr/include/math.h' is just full of
defines and the header files it includes are also a bunch
of defines with a few macro functions sprinkled in. Can someone
shed light on if this is bad or not and why it would be done
or necessary? Thanks.

-Steve

-- 
 Steven J. Hill - Embedded SW Engineer
 Public Key: 'http://www.cotw.com/pubkey.txt'
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Re: Question on including 'math.h' from C runtime...

[Horst von Brand]

"Steven J. Hill" <sjhill@cotw.com> said:
> I checked in the archives and did not see a discussion of this
> anywhere. I have received some Linux kernel code from a project
> that I have inherited and a couple of the drivers are including
> math.h from the C library. This being the header file from
> '/usr/include/math.h' in most cases. There are only two places
> in the kernel that also include this header file. They are:
> 
>    drivers/atm/iphase.c
>    drivers/net/hamradio/soundmodem/gentbl.c
> 
> As far as I can tell '/usr/include/math.h' is just full of
> defines and the header files it includes are also a bunch
> of defines with a few macro functions sprinkled in. Can someone
> shed light on if this is bad or not and why it would be done
> or necessary? Thanks.

Floating point in-kernel is a no-no-no. What you see is use in helper
programs that are compiled as part of the kernel build. Check if that is
your case too.
-- 
Horst von Brand                             vonbrand@sleipnir.valparaiso.cl
Casilla 9G, Vin~a del Mar, Chile                               +56 32 672616

Re: Question on including 'math.h' from C runtime...

[Alan Cox]

> '/usr/include/math.h' in most cases. There are only two places
> in the kernel that also include this header file. They are:
> 
>    drivers/atm/iphase.c

That probably shouldnt be using it

>    drivers/net/hamradio/soundmodem/gentbl.c

This one is intentional. gentbl is a program linked in user space and used
to generate a .h file then built for the kernel