Hi,
I am implemeting a new system call for a project I'm working on. I added
the system call to the file arch/i386/kernel/process.c and added the
relevant entries in the files arch/i386/entry.S and
include/asm-i386/unistd.h. My system call is made up of only two lines,
a printk statement, and a return statement which gets the value of a
field that I added to the task_struct structure.
I compiled and booted the kernel and am trying to build a user space
application that uses my system call, however gcc is returning this error:
/tmp/cc4zgzUr.o(.text+0x4e): In functiono `get_rmt_paging':
: undefined reference to `errno'
Can anyone help me with this?
Thanks
Josef
On Sat, 2005-02-26 at 15:17 +0100, Josef E. Galea wrote:
> I compiled and booted the kernel and am trying to build a user space
> application that uses my system call, however gcc is returning this error:
> /tmp/cc4zgzUr.o(.text+0x4e): In functiono `get_rmt_paging':
> : undefined reference to `errno'
>
Where you defined your system call in the user space program (ie. where
you declared your _syscall macro), did you also include <errno.h>?
-- Steve
Steven Rostedt wrote:
>On Sat, 2005-02-26 at 15:17 +0100, Josef E. Galea wrote:
>
>
>
>>I compiled and booted the kernel and am trying to build a user space
>>application that uses my system call, however gcc is returning this error:
>>/tmp/cc4zgzUr.o(.text+0x4e): In functiono `get_rmt_paging':
>>: undefined reference to `errno'
>>
>>
>>
>
>Where you defined your system call in the user space program (ie. where
>you declared your _syscall macro), did you also include <errno.h>?
>
>-- Steve
>
>
>
>
I included <linux/errno.h> and it didn't solve the problem. Now i
included <errno.h> and it did. Thanks for you help!
Josef
On Sat, 26 Feb 2005, Josef E. Galea wrote:
> Hi,
>
> I am implemeting a new system call for a project I'm working on. I added the
> system call to the file arch/i386/kernel/process.c and added the relevant
> entries in the files arch/i386/entry.S and include/asm-i386/unistd.h. My
> system call is made up of only two lines, a printk statement, and a return
> statement which gets the value of a field that I added to the task_struct
> structure.
>
> I compiled and booted the kernel and am trying to build a user space
> application that uses my system call, however gcc is returning this error:
> /tmp/cc4zgzUr.o(.text+0x4e): In functiono `get_rmt_paging':
> : undefined reference to `errno'
>
> Can anyone help me with this?
>
> Thanks
> Josef
You can't use kernel headers in user-mode functions. For one thing,
they bring in undefined stuff.
Your user mode code can, of course get the definition of errno
by #include <errno.h>. That's the errno that exists in every user-
mode 'C' program-developed process space. However, if get_rmt_paging
is not one of your functions, you are in trouble by mixing up
user-mode and kernel-mode headers.
Normally, the return value of a kernel function is checked and
if it's negative, the positive equivalent is put into the global
variable errno and then the return value is changed to -1. This
is where the user-mode reference to errno occurs.
Cheers,
Dick Johnson
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