I've recently upgraded my kernel (from 2.4.31 to 2.6.19) and also my toolchain, and now I'm getting undefined references.

e.g.

:/home/mike/work/sensor/sensor.c:80: undefined reference to `i2c_smbus_write_block_data'
:/home/mike/work/sensor/sensor.c:95: undefined reference to `i2c_smbus_write_byte'
:/home/mike/work/sensor/sensor.c:107: undefined reference to `i2c_smbus_read_word_data'
collect2: ld returned 1 exit status
make: *** [sensor] Error 1

These routines are part of the i2c dev interface and appear to have been moved into the kernel from 2.6.13 onwards.

How do I get the linker to resolve these undefined references ? Is there some sort of special calling mechanism now that they are part of the kernel ?

i think we need the compiler output including the link command that failed.

the i2c-bus works right it's just a compile problem.
we might need to know what you are compiling.

when you say you upgraded you toolcain you mean you have a new glibc too ?

Thanks for the reply.

The command looks like ...

/home/mike/buildroot/build_i386/staging_dir/bin/i386-linux-uclibc-gcc -Wall -o sensor sensor.o sensor_utils.o -L/home/mike/buildroot/build_i386/staging_dir/lib -L/home/mike/buildroot/build_i386/staging_dir/i386-linux-uclibc/lib -L/home/mike/buildroot/build_i386/staging_dir/usr/lib -lm -lc --just-symbols=~/linux-2.6.19.1/System.map
sensor.o: In function `main':
/home/mike/work/sensor/sensor.c:77: undefined reference to `i2c_smbus_read_byte_data'
/home/mike/work/sensor/sensor.c:84: undefined reference to `i2c_smbus_write_block_data'
/home/mike/work/sensor/sensor.c:99: undefined reference to `i2c_smbus_write_byte'
/home/mike/work/sensor/sensor.c:111: undefined reference to `i2c_smbus_read_word_data'
collect2: ld returned 1 exit status
make: *** [sensor] Error 1
[mike@glynys sensor]$

As you can see I'm using uClibc because it's a small embedded system I'm trying to set up. I've also tried using the --just_symbols and -t options to the linker with no effect.

The routines I need are in the kernel. How do I link to them ?

hi,
im not sure about this but
include <linux/i2c-dev.h>

would be a part of glibc BUT the glibc has to be compiled against the kernel headers from the newer kernel.

i think in an embeded system it is common to use a minimal subset of glibc symbols.
there is a method they use where when they encounter an undefined reference they can add the symbol to a symbol list and recompie glibc to include it but this is beyond my ability to comment on further. sorry