fpt and WinFPT Reference Manual - Command-line Commands

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CHECK ARRAY BOUNDS and INSERT ARRAY BOUNDS CHECKS

Syntax:

[DO NOT] CHECK [ARRAY] BOUNDS [DO NOT] INSERT [ARRAY] BOUNDS CHECK[S]

Function:

fpt checks that array indices are within the bounds declared for the array. There are six possible situations:

• The array index is a constant and is within the declared bounds. This is correct. No report is made and no bounds check is inserted in the code.
• The array index is a constant and is outside the declared bounds.
   
  If the command CHECK ARRAY BOUNDS is made the error is marked in the code and is reported.
   
  If the command INSERT ARRAY BOUNDS CHECKS is made a check is inserted in the code and no static error is reported. This is done because the code may be unreachable in the situation where the out-of-bounds reference would occur, and there would therefore be no error. If the code is reachable, an error is reported at run-time.
• The array index is a variable. fpt identifies the relevant assignments of the variable and finds that the possible range of values is within the declared bounds of the array. The variable may, for example, be a DO loop index with a conforming range of values. This is correct. No report is made and no bounds check is inserted in the code.
• The array index is a variable. fpt identifies the relevant assignments and finds that the variable is expected to take values outside the array bounds. This is expected to be an error.
   
  If the command CHECK ARRAY BOUNDS is made the error is marked in the code and is reported.
   
  If the command INSERT ARRAY BOUNDS CHECKS is made a check is inserted in the code and no static error is reported. Again, this is done because the code may be unreachable in the situation where the out-of-bounds reference would occur, and there would therefore be no error. If the code is reachable, an error will be reported at run-time.
• The array index is a variable. fpt identifies the relevant assignments but is unable to determine the range of possible values.
   
  If the command CHECK ARRAY BOUNDS is made no error is marked in the code and there is no report.
   
  If the command INSERT ARRAY BOUNDS CHECKS is made a check is inserted in the code. If the code is reached with an index which is out-of-bounds an error will be reported at run-time.
• One or both of the array bounds is variable. The array may, for example, be a formal argument with variable bouinds. At present, no report is made and no check is inserted.

Inserting Bounds Checks in the Code

In the statement:

n = arr(i,j)

where arr is declared arr(2,10), the variables i and j are of type INTEGER*4 and both indices are to be checked, fpt inserts calls to the fpt library routine fpt_check_bounds_i4 as shown below:

CALL fpt_check_bounds_i4(1234, i, 1, 2) CALL fpt_check_bounds_i4(1235, j, 1, 10) n = arr(i,j)

where 1234 and 1235 are unique identifiers for the bounds checks, and 1, 2 and 1, 10 are the bounds against which i and j are checked. The library contains bounds check routines for 1, 2, 4 and 8-byte integers and 4 and 8-byte reals.

Occasionally a situation arises where a bounds check cannot be inserted as a separate statement. For example:

IF (arr(i,j) > 5) THEN ! 1 WRITE(6,'("Detected arr(i,j) > 5")') ELSEIF (arr(i,j) < 1) THEN ! 2 WRITE(6,'("Detected arr(i,j) < 1")') ENDIF

In this situation the array reference at 2 cannot be checked by inserting a separate statement. The code is modified:

CALL fpt_check_bounds_i4(1236, i, 1, 2) CALL fpt_check_bounds_i4(1237, j, 1, 10) IF (arr(i,j) > 5) THEN ! 1 WRITE(6,'("Detected arr(i,j) > 5")') ELSEIF (arr(fpt_check_bounds_i4_fun(1238, i, 1, 2), & fpt_check_bounds_i4_fun(1239, j, 1, 10)) < 1) THEN ! 2 WRITE(6,'("Detected arr(i,j) < 1")') ENDIF

Again a set of functions is supplied for different integer and real kinds. The value returned by each function is the value of the index tested. Declarations of the functions are inserted automatically where they are needed.

The bounds check subroutines and functions do not halt the program in the same way as a bounds check inserted by a compiler. They simply increment a counter within an array which is indexed by the unique identifier for each check. This array is initialised to zero by the fpt library subroutine fpt_init_bounds_check and a call to this routine is inserted at the start of the main program. The non-zero elements of this array are reported by the subroutine fpt_write_bounds_check and calls to this routine are inserted at every exit point from the program. The results are written to the file fpt_bounds_check.txt. This is convenient if significant work is involved in setting up a program to make a bounds check. All of the out-of-bounds references can be caught in one program run.

Recommended use of the INSERT ARRAY BOUNDS CHECKS Command

Add the fsp file FPTMAIN:insert_bounds_checks.fsp at the end of the fsp or fpp file for the project. This file contains the INSERT ARRAY BOUNDS CHECKS command and the appropriate library references.

Where to use the CHECK ARRAY BOUNDS command:

Where to use the INSERT ARRAY BOUNDS CHECKS command:

Default

Array bounds with constant indices are checked by default. Those with variable indices are not, and no bounds check is inserted by default (Note that defaults may be changed in the configuration file).

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