C function from 7.3.2 to 7.4.3

Greetings,

I have some C functions (was compiled against 7.3.2, I think)

CREATE FUNCTION "mud" () RETURNS TRIGGER AS '/xxx/pgsql/lib/du.so',
'mud' LANGUAGE 'C';

It runs fine under 7.3.2, but I will get error when run the above CREATE
FUNCTION under 7.4.3.

ERROR: could not load library "/xxx/lib/du.so": /xxx/lib/du.so:
undefined symbol: elog

The 7.3.2 version is under /xxx/pgsql and 7.4.3 is under /tmp/pgsql

I have LD_LIBRARY_PATH and PGLIB to include /xxx/pgsql/lib

Do I need to re-compile C functions against 7.4.3 or something else I
missed?

I have tried to copy du.so from /xxx/pgsql/lib to /tmp/pgsql/lib and got
the same error.

Thanks,