try including #include <linux/errno.h>. You should include /usr/src/linux_x_y_z/include include and not the just /usr/include while working with modules. Raghu On Fri, 20 Feb 2004, cam wrote: > Hello all, > > I'm attempting to do some work with the sysctl interface from a module. I am > able to correctly build my module using make modules but I get the "undefined > reference to errno" when I attempt the make modules_install step. > > Some trawling on the net has revealed that this started happening with various > source trees using older conventions e.g. from > > http://www.compusys.co.uk/Compusys/HPC/Cluster+Admin+Tips/Compilation+errors+with+GCC+Version+3.2+and+Open+PBS+version+2.3.16.htm > ------------------------------------------------------- > "Since version 2.9 of the GCC compiler the compiler has become a lot stricter > over declaring external references. > Undefined reference to ?errno? > > In most cases this is not a problem, but only when the programming of a library > has become slightly lax. Once common error is to use the phrase: > > extern int errno; > > in c code rather than the correct method of: > > #include <errno.h> > > This can be seen in a few of the libraries supplied with Open PBS. To fix this > problem cd to the directory which includes the source code and type the > following command: > > grep -rs ?extern int errno? * > > If any files return as having the line, then replace the line with the correct > version as shown above, using your favourite text editor." > ------------------------------------------------------- > > When I run this against my development tree, the only place errno is defined is > in include/linux/unistd.h I notice on the lxr site that this is currently valid > code. > > For some background, my module is a networking component and I need to fetch > some /proc info. Since I am in the kernel I can't use the userspace sysctl lib > and have to: > > #include <linux/sysctl.h> > #include <linux/unistd.h> > > and use the syscall1 macro. This part of the code seems fine. In order to test > it, I tried a small userspace program which generated the same "unreferenced > errno" error until I did the following : > > #include <linux/errno.h> > > Now the userspace example works but it doesn't fix the module. > > WTF is going on here? I don't know enough about this to fix it but I'd be > grateful for any pointers even if its to a site or book worth reading about > this because I know my ignorance of compiling and linking isn't helping me > here. I have taken a look at Johnson & Troans "Linux Application Development" > and Rubini's "Understanding the Linux Kernel" but there is very little > discussion of the linking phase of a kernel build. > > There are so many returns for this on google that it must have tripped up a few > people - just none of the solutions match my problem. > > Any help gratefully received, > cam > > __________________________________ > Do you Yahoo!? > Yahoo! Mail SpamGuard - Read only the mail you want. > http://antispam.yahoo.com/tools > > -- > Kernelnewbies: Help each other learn about the Linux kernel. > Archive: http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
