CVC:
This is how v1's ib_udf parameters look in system tables.
Comparing this file against ib_udf2_params.txt we get ib_udf_upgrade.sql
that will take us from v1's ib_udf to v2's ib_udf.

RDB$FUNCTION_NAME               RDB$ARGUMENT_POSITION RDB$MECHANISM 
=============================== ===================== ============= 

ABS                                                 0             0 
ABS                                                 1             1 
ACOS                                                0             0 
ACOS                                                1             1 
ASCII_CHAR                                          0            -1 
ASCII_CHAR                                          1             1 
ASCII_VAL                                           0             0 
ASCII_VAL                                           1             1 
ASIN                                                0             0 
ASIN                                                1             1 
ATAN                                                0             0 
ATAN                                                1             1 
ATAN2                                               0             0 
ATAN2                                               1             1 
ATAN2                                               2             1 
BIN_AND                                             0             0 
BIN_AND                                             1             1 
BIN_AND                                             2             1 
BIN_OR                                              0             0 
BIN_OR                                              1             1 

RDB$FUNCTION_NAME               RDB$ARGUMENT_POSITION RDB$MECHANISM 
=============================== ===================== ============= 
BIN_OR                                              2             1 
BIN_XOR                                             0             0 
BIN_XOR                                             1             1 
BIN_XOR                                             2             1 
CEILING                                             0             0 
CEILING                                             1             1 
COS                                                 0             0 
COS                                                 1             1 
COSH                                                0             0 
COSH                                                1             1 
COT                                                 0             0 
COT                                                 1             1 
DIV                                                 0             0 
DIV                                                 1             1 
DIV                                                 2             1 
FLOOR                                               0             0 
FLOOR                                               1             1 
LN                                                  0             0 
LN                                                  1             1 
LOG                                                 0             0 

RDB$FUNCTION_NAME               RDB$ARGUMENT_POSITION RDB$MECHANISM 
=============================== ===================== ============= 
LOG                                                 1             1 
LOG                                                 2             1 
LOG10                                               0             0 
LOG10                                               1             1 
LOWER                                               0            -1 
LOWER                                               1             1 
LPAD                                                0            -1 
LPAD                                                1             1 
LPAD                                                2             1 
LPAD                                                3             1 
LTRIM                                               0            -1 
LTRIM                                               1             1 
MOD                                                 0             0 
MOD                                                 1             1 
MOD                                                 2             1 
PI                                                  0             0 
RAND                                                0             0 
RPAD                                                0            -1 
RPAD                                                1             1 
RPAD                                                2             1 

RDB$FUNCTION_NAME               RDB$ARGUMENT_POSITION RDB$MECHANISM 
=============================== ===================== ============= 
RPAD                                                3             1 
RTRIM                                               0            -1 
RTRIM                                               1             1 
SIGN                                                0             0 
SIGN                                                1             1 
SIN                                                 0             0 
SIN                                                 1             1 
SINH                                                0             0 
SINH                                                1             1 
SQRT                                                0             0 
SQRT                                                1             1 
STRLEN                                              0             0 
STRLEN                                              1             1 
SUBSTR                                              0            -1 
SUBSTR                                              1             1 
SUBSTR                                              2             1 
SUBSTR                                              3             1 
SUBSTRLEN                                           0            -1 
SUBSTRLEN                                           1             1 
SUBSTRLEN                                           2             1 

RDB$FUNCTION_NAME               RDB$ARGUMENT_POSITION RDB$MECHANISM 
=============================== ===================== ============= 
SUBSTRLEN                                           3             1 
TAN                                                 0             0 
TAN                                                 1             1 
TANH                                                0             0 
TANH                                                1             1