Error: undefined symbol: hm2_pktuart_setup_rx - while lading custom modbus.so

Sorry, apparently I didn't read your complete post. I'll try again

I get an access denied error if I modcompile without sudo. Can that be the issue?

sudo modcompile works, but again the same error.

it should be:

modcompile xxxx.mod

not

sudo modcompile xxxx.mod

at least that's what I have always done

 

With a fress install (from image) - without sudo i get this;

corne@linuxcnc:~/CNC/Mesa/mod$ modcompile mb25ioc32.mod
/tmp/tmpqf_2s56r/mesa_modbus.c
touch: cannot touch 'mesa_modbus.c': Permission denied
Compiling realtime mesa_modbus.c
Linking mb25ioc32.so
cp mb25ioc32.so /usr/lib/linuxcnc/modules/
cp: cannot create regular file '/usr/lib/linuxcnc/modules/mb25ioc32.so': Permission denied
make: *** [/usr/share/linuxcnc/Makefile.modinc:107: install] Error 1

I changed the permissions of the modules directory. Now only a 'touch' error. Doesn't say me something...

corne@linuxcnc:~/CNC/Mesa/mod$ modcompile mb25ioc32.mod
/tmp/tmp40_g_2ol/mesa_modbus.c
touch: cannot touch 'mesa_modbus.c': Permission denied
Compiling realtime mesa_modbus.c
Linking mb25ioc32.so
cp mb25ioc32.so /usr/lib/linuxcnc/modules/

OK  thinking about this, it's probably just a difference between a RIP installation and
a binary installation, where the normal user does not have write access to LinuxCNC's
system files.

Still does not explain the issue, and why it works as expected using  2.9.4 built from source.
Maybe a problem with the binary image.

 

Here are the pktuart.0 and mb25ioc32.so files that work on my system:

 

Replacing your files (one at a time) may help debug this issue.

Copied the mb25ioc32.so to the modules directory > same result as mentioned in my initial post.
A search to *pktuart* doesn't give any hit. So I don't know where to place these.

A compile of mb25ioc32.so delivers a mesa_modbus.o (and .c) in a tmp directory. I can find the source of this file at /usr/share/linuxcnc/ as mesa_modbus.o.tmpl.

locate pktuart
 
should find it but if you have re installed recently the
locate database has probably not been updated
(its done periodically, usually scheduled late at night)

You can manually update the locate database with:

sudo updatedb

(this will take a while since is has to search the entire directory system)