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Problems compiling kernel modules

DISCUSSION Lei Yang 8 participants 21 messages Aug 21, 2004 – Aug 23, 2004

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Lei Yang

author
#0 lore raw

Hi all,

I was trying to compile a kernel module with kbuild. The module 'test.c' include a header file 'fred.h' and there is a "#include <stdio.h>" in 'fred.h'.

Makefile looks like:

------------------------------------------------------------------------
ifneq ($(KERNELRELEASE),)
obj-m := test.o

else
KDIR := /usr/src/linux
PWD := $(shell pwd)

default:

	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

clean:
rm -f *.o *.ko *.mod.c *.mod.o \
.test.o.cmd .test.ko.cmd .test.mod.o.cmd
rm -rf .tmp_versions
endif

-------------------------------------------------------------------------
But upon compiling, there would be errors like this:
In file included from /home/lei/test.c:49:
/home/lei/fred.h:4:19: stdio.h: No such file or directory

and a lot of undeclared names follow which I assume is from stdio.h.

Could anyone point out what's wrong here?

TIA!

Lei

#1 lore raw
Quoted 16 lines · Lei Yang

Hi all,

I was trying to compile a kernel module with kbuild. The module 'test.c' include a header file 'fred.h' and there is a "#include <stdio.h>" in 'fred.h'.

Makefile looks like:

------------------------------------------------------------------------
ifneq ($(KERNELRELEASE),)
obj-m := test.o

else
KDIR := /usr/src/linux
PWD := $(shell pwd)

Quoted 5 lines

default:

	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

clean:

For 2.6.7 (or 2.6.6) you do not need to specify your own clean: rule.

Quoted 3 lines

But upon compiling, there would be errors like this:
In file included from /home/lei/test.c:49:
/home/lei/fred.h:4:19: stdio.h: No such file or directory

The kernel does not provide you with a stdio.h header, so therefore you cannot find it neither use functionality from it.

Sam

author
#2 lore raw
Quoted 25 lines · Sam Ravnborg
Quoted 14 lines · Lei Yang

Hi all,

I was trying to compile a kernel module with kbuild. The module 'test.c' include a header file 'fred.h' and there is a "#include <stdio.h>" in 'fred.h'.

Makefile looks like:

------------------------------------------------------------------------
ifneq ($(KERNELRELEASE),)
obj-m := test.o

else
KDIR := /usr/src/linux
PWD := $(shell pwd)

Quoted 5 lines

default:

	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

clean:

For 2.6.7 (or 2.6.6) you do not need to specify your own clean: rule.

Quoted 6 lines
Quoted 3 lines

But upon compiling, there would be errors like this:
In file included from /home/lei/test.c:49:
/home/lei/fred.h:4:19: stdio.h: No such file or directory

The kernel does not provide you with a stdio.h header, so therefore you cannot find it neither use functionality from it.

You mean I can't use stdio.h at all?

But what if I really need to? Is there anything I can do?

Quoted 1 line

Sam

#3 lore raw
Quoted 2 lines · Lei Yang

You mean I can't use stdio.h at all?

Correct.

Quoted 2 lines

But what if I really need to? Is there anything I can do?

Try to explain what you need. Then maybe someone on the list can help you.

Sam

author
#4 lore raw
Quoted 9 lines · Sam Ravnborg
Quoted 1 line · Lei Yang

You mean I can't use stdio.h at all?

Correct.

Quoted 1 line

But what if I really need to? Is there anything I can do?

Try to explain what you need. Then maybe someone on the list can help you.

I need to do File I/O operation and I need to use streams.

Thanks,
Lei

#19 lore raw
In reply to Lei Yang
Quoted 1 line · Lei Yang

You mean I can't use stdio.h at all?

Not in the kernel code.

Quoted 1 line

But what if I really need to?

Then you are really out of luck.

Quoted 1 line

Is there anything I can do?

A lot of things - hopefully your life is not reduced to trying to write stdio-dependent kernel modules...

#20 lore raw
In reply to Lei Yang
Quoted 3 lines · Lei Yang

You mean I can't use stdio.h at all?

But what if I really need to?

LOL, the above needs to go in the FAQ.

Lee

author
#5 lore raw
In reply to Sam Ravnborg

What about multi-file module?

Say test.c doesn't include stdio.h, while there is some other .c file which is to be compiled and linked into test.ko, include stdio?

Would that work?

TIA!
Lei

Quoted 11 lines · Sam Ravnborg
Quoted 1 line · Lei Yang

You mean I can't use stdio.h at all?

Correct.

Quoted 1 line

But what if I really need to? Is there anything I can do?

Try to explain what you need. Then maybe someone on the list can help you.

Sam

#6 lore raw
Quoted 7 lines · Lei Yang

What about multi-file module?

Say test.c doesn't include stdio.h, while there is some other .c file which is to be compiled and linked into test.ko, include stdio?

Would that work?

Are you just trying to print from a kernel module? Use printk.

The kernel does not really have its own standard input and standard output - the kernel manages those things for processes.

Lee

#18 lore raw
In reply to Lei Yang
Quoted 8 lines · Lei Yang

What about multi-file module?

Say test.c doesn't include stdio.h, while there is some other .c file which is to be compiled and linked into test.ko, include stdio?

Would that work?

TIA!
Lei

You can't use userspace headers in the kernel. That's why the kernel has its own set with things like printk(), etc, etc. What is it that you're trying to do and why does it need file i/o?

Signature · 2 lines
Alex Goddard
agoddard at purdue dot edu
author
#7 lore raw
In reply to Lee Revell

Hi friends,

I've askeed questions about errors compiling kernel modules caused by including <stdio.h> and got some very helpful info here.

I changed those I/O stream and file operation in the code and get the module compiled, however, there would be warnings like

In file included from /home/lei/modules/test.c:49:
/home/lei/modules/Kcomp.h:21: warning: function declaration isn't a prototype /home/lei/modules/Kcomp.h:27: warning: function declaration isn't a prototype /home/lei/modules/Kcomp.h:69: warning: function declaration isn't a prototype

And the no prototype fuction looks like

int preset() // with no arguments

{
	p = &nodes[0][0];
	return 0;
}

So when I tried to install the module with insmod ./test.ko , there would be an error,

insmod: error inserting './test.ko': -1 Unknown symbol in module

Could anyone tell me what is wrong here? Is that because of the no prototype function declaration?

TIA
Lei

Quoted 17 lines · Lee Revell
Quoted 6 lines · Lei Yang

What about multi-file module?

Say test.c doesn't include stdio.h, while there is some other .c file which is to be compiled and linked into test.ko, include stdio?

Would that work?

Are you just trying to print from a kernel module? Use printk.

The kernel does not really have its own standard input and standard output - the kernel manages those things for processes.

Lee

#8 lore raw
Quoted 16 lines · Lei Yang

Hi friends,

I've askeed questions about errors compiling kernel modules caused by including <stdio.h> and got some very helpful info here.

I changed those I/O stream and file operation in the code and get the module compiled, however, there would be warnings like

In file included from /home/lei/modules/test.c:49:
/home/lei/modules/Kcomp.h:21: warning: function declaration isn't a prototype
/home/lei/modules/Kcomp.h:27: warning: function declaration isn't a prototype
/home/lei/modules/Kcomp.h:69: warning: function declaration isn't a prototype

Quoted 8 lines

And the no prototype fuction looks like

int preset() // with no arguments

{
	p = &nodes[0][0];
	return 0;
}

A function looks like this:

int present()
{

}

A prototype for the same function looks like this:

int present(void);

Functions always have "{}". Prototypes never do. -- Yes there's some troll who might cite some obscure case... ignore them.

If you compile above a certain warning-level, then prototypes are required. The prototype usually goes in header files and the function (the actual code) goes in the source files.

Quoted 9 lines

So when I tried to install the module with insmod ./test.ko , there would be an error,

insmod: error inserting './test.ko': -1 Unknown symbol in module

Could anyone tell me what is wrong here? Is that because of the no prototype function declaration?

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.

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

author
#9 lore raw
Quoted 6 lines · Richard B. Johnson

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

Quoted 7 lines

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

#10 lore raw
Quoted 18 lines · Lei Yang
Quoted 6 lines · Richard B. Johnson

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

Quoted 8 lines

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.

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

author
#11 lore raw
Quoted 32 lines · Richard B. Johnson
Quoted 19 lines · Lei Yang
Quoted 6 lines · Richard B. Johnson

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

Quoted 8 lines

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

Quoted 8 lines

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

Quoted 6 lines

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

#12 lore raw
Quoted 5 lines · Lei Yang

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?

Before helping out more with your compile issue please explain in propser detail what you try to achive.
Reading the above I get the impression you thing a library will run faster when running in kernel context - and thats what you try to do.

If this is your plan then the answer is: Drop it.

Sam

#15 lore raw
In reply to Lei Yang
Quoted 42 lines · Lei Yang
Quoted 32 lines · Richard B. Johnson
Quoted 19 lines · Lei Yang
Quoted 6 lines · Richard B. Johnson

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

Quoted 8 lines

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

Quoted 8 lines

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.

Quoted 7 lines

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).

Quoted 7 lines
Quoted 6 lines

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.

author
#13 lore raw
In reply to Sam Ravnborg
Quoted 11 lines · Sam Ravnborg
Quoted 1 line · Lei Yang

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?

Before helping out more with your compile issue please explain in propser detail what you try to achive.
Reading the above I get the impression you thing a library will run faster when running in kernel context - and thats what you try to do.

If this is your plan then the answer is: Drop it.

NO, this is not my plan :)

I was trying to build a compression/decompression utility with my algorithm in kernel, and want to use it in some of the device drivers. And in that algorithm, we need floating-point.

Thanks!
Lei

#17 lore raw
In reply to Richard B. Johnson
Quoted 5 lines · Richard B. Johnson

A function looks like this:

int present()
{

Quoted 7 lines

}

A prototype for the same function looks like this:

int present(void);

Functions always have "{}". Prototypes never do.

A function definition is also a prototype unless you use oldstyle definitions.

Andreas.

Signature · 4 lines
Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux AG, Maxfeldstraße 5, 90409 Nürnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."
#16 lore raw
In reply to Lei Yang
Quoted 9 lines · Lei Yang

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

Quoted 3 lines

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.

You are correct - the kernel doesn't support floating point operations used in kernel space unless you do some fairly tricky stuff.

#14 lore raw
In reply to Lei Yang
Quoted 3 lines · Lei Yang

I was trying to build a compression/decompression utility with my algorithm in kernel, and want to use it in some of the device drivers. And in that algorithm, we need floating-point.

In which case the best place to look (if it needs to be kernel side) is probably drivers/md/ which shows how you can use the FPU state. There is a cost to it as you have to save/restore the user FP state and on x86 that is expensive of course.

Historically we've always tried to keep compression algorithms in user space. The video4linux layer for example pushes most of this to the user and that allows the user program to make a more intelligent assessment of the input format and desired target. This avoids things like kernel drivers turning data from one format to another and user space libraries turning it back again.

Alan