Re: Problems compiling kernel modules

[Richard B. Johnson]

On Mon, 23 Aug 2004, Lei Yang wrote:

> Richard B. Johnson wrote:
> > On Mon, 23 Aug 2004, Lei Yang wrote:
> >
> >
> >>Richard B. Johnson wrote:
> >>
> >>
> >>>Do `depmod -e test.ko` to see what it's complaining about. You
> >>>can see all the symbols by using `nm`. Try it. Your code
> >>>probably didn't define the necessary stuff to make a module.
> >>>You need to look at a typical module (driver) that comes with the
> >>>kernel. Just find one of the shortest ".c" files in the driver
> >>>tree.
> >>
> >>Thanks! I did less /var/log/messages, and got the unknown symbols
> >>Unknown symbol __divsf3
> >>Unknown symbol __fixsfsi
> >>Unknown symbol __subsf3
> >>Unknown symbol __floatsisf
> >>Unknown symbol __mulsf3
> >>Unknown symbol __gesf2
> >>Unknown symbol __addsf3
> >>
> >>However, I don't know what those symbols are :( I am a bit worried that
> >>maybe I've done something that is not supported by the kernel, like
> >>left-shift 16 bits of an int, or floating operations.
> >>
> >>Any hints?
> >>
> >>Thanks a lot!
> >>Lei
> >
> >
> > You cannot use floating-point in the kernel. It appears that you
> > are trying to make user-mode code execute within the kernel. It
> > can't. That's not what a module does. The kernel executes code
> > on behalf of the user-mode caller, in the context of the caller.
> > It does things, on behalf of the user, that the user can't
> > be trusted to do properly by himself. That's all the kernel
> > is for! Any calculations and similar stuff can be done in
> > regular user-mode code.
>
> Sort of, I am trying to make a usr mode library work with kernel.
> However, floating point operation is necessary in the algorithm. You
> mean that this can never be done? Is changing floating-point the only
> thing I can do now?
>
> Thanks!
> Lei

Let's put it this way. If you think you need to use a floating-point
library inside the kernel, then you don't understand what the kernel
does or what it was designed to do. You should make a module that
reads from, or writes to, the special hardware you are using. Then,
using user mode code (called a daemon), you read from the device,
perform the floating-point processing, then write to the device.
That way, you are using the kernel priviliges only for reading/writing
to the device.

It is possible to execute floating point code within the kernel
if the context of the floating-point unit is saved first, and
restored after the operation. However, you will never get a
math library to work inside the kernel unless you write your
own. You cannot use the 'C' runtime library inside the kernel.
That library was designed to be outside the kernel (it uses
the kernel).


> > Cheers,
> > Dick Johnson
> > Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips).
> >             Note 96.31% of all statistics are fiction.
> >
> >
>

Cheers,
Dick Johnson
Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips).
            Note 96.31% of all statistics are fiction.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/