[etherlab-users] Linker problems with stable-1.5 patched with the latest rtdm-patch

[Richard Hacker]

On Monday 12 March 2012 21:39:28 WIEGAND Ralf wrote:
> Hello Graeme,
> 
> first of all, thanks for the great job on the rtdm-patch.
> 
> I am trying to use your latest rtdm-patch for the stable-1.5 on revision
>  2266 and get some problems during linking my own application. There are
>  undefined references to every ecrt_rtdm_*** library function. I use the
>  linker-flags "-L/usr/realtime/lib -L/opt/etherlab/lib" and "-llxrt -lrtdm
>  -lethercat". The patch, compilation and installation of the master runs
>  without any problems. The ld is configured to search libraries under
>  /usr/realtime/lib and /opt/etherlab/lib.
... but libc probably isn't ;)

While you told your linker where to find libetherlab.so (by using 
-L/opt/etherlab/lib), libc (actually libdl.so.2) does not know where to find 
it. If you call ldd on your executable, you should find that libetherlab.so is 
not resolved.

To tell libdl.so.2 where to find the library, you must use the option rpath in 
the linking stage of ld:
ld -o <executable> <objects>.o \
	-L/opt/etherlab/lib -rpath=/opt/etherlab/lib -letherlab
or with gcc:
gcc -o <executable> <objects>.o \
	-L/opt/etherlab/lib -Wl,-rpath=/opt/etherlab/lib -letherlab

Alternatively you can configure it system wide by adding the line
/opt/etherlab/lib
to /etc/ld.so.conf
or added a file /etc/ld.so.conf.d/ethercat.conf with the directory included. 
Thereafter run ldconfig as root (instead of rebooting, which will also work... 
but we're not using Windows here ;) )

Now calling ldd on your executable should show libetherlab.so being resolved.

>  I also checked the content of the
>  libethercat library with readelf, but all called library-functions are
>  listed in the output. When i try to read out the ELF information with
>  readelf of the ec_rtai_rtdm_example, i get an error that the file isn't an
>  ELF-file.
It is probably statically linked to libethercat.a, although I am not conviced 
thereof.

> 
> My system is debian based (lenny) with kernel 2.6.32.11 and rtai-3.8.1.
> 
> Do you or anybody on the list have any idea to solve the problem or give me
>  a hint ?
> 
> 
> Regards,
> 
> Ralf Wiegand
> 
> 
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> 
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> 
> 
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> 

Mit freundlichem Gruß

Richard Hacker

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Richard Hacker M.Sc. 
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