Guardian Procedure Calls Reference Manual (G06.25+)

Introduction to Guardian Procedure Calls

Guardian Procedure Calls Reference Manual—522629-013

1-10

String Output Variables

The syntax for some Guardian procedures contains one or more sets of three

parameters that are grouped together, where each set describes a string output

variable. Figure 1-2

shows an example of this use.

Note that the first two parameters are separated by a colon. (See Figure 1-1

for a

general description of the use of two parameters separated by a colon.) The

filename parameter is an output parameter that contains a character string on return;

maxlen is an input parameter that specifies the maximum number of characters that

can be returned in

filename; filename-length is an output parameter that returns

the actual number of characters returned in

filename.

When three parameters are grouped in this fashion, all of them must be either present

or absent. If only one or two of them are present, an error is returned.

Reference Parameter Overlap

No variable that you supply as an output parameter in a call to a Guardian procedure

should have the same address as, or overlap, any other reference parameter to the

procedure. The only exceptions to this occur where the procedure description explicitly

allows such use.

Bounds Checking of Reference Parameters for

Guardian Procedures

Starting in the D20 RVU, bounds checking of reference parameters to Guardian

procedures is different. The change does not affect programs that call procedures with

correct parameters that are within bounds; these programs will continue to work

correctly.

In some cases where reference parameters to Guardian procedures point to areas that

were formerly considered out of bounds, the procedure might not detect the error. If the

out-of-bounds parameter would either breach security or compromise system integrity,

however, it will continue to be detected.

As an example, many Guardian procedures now use a local data stack that is separate

from the user’s local data stack. Prior to D20, it was an error to specify a reference to

an array that extended beyond the end of the user’s local data area into the data area

of the called Guardian procedure. Starting in D20, you cannot rely on a Guardian

procedure to return an error when you specify a reference parameter in this manner.

Figure 1-2. Syntax With String Output Variable

error := PROCESSHANDLE_TO_FILENAME_ ( processhandle ! i

,filename:maxlen ! o:i

,filename-length ! o

. . .