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Administrative and Operational Enhancements › SVC Screening Control

SVC Screening Control

You can now allow additional SVCs to be issued from within a DC/UCF system by specifying the new DISABLE_SVC_SCREEN parameter for SYSIDMS.

SVC screening enables COBOL II, LE COBOL, PL/I and C programs to execute within the DC/UCF address space by substituting a DC service call in place of supported SVCs issued by the high-level language. For example, a GETMAIN is translated to a GET STORAGE request. If an assembler program or an unsupported high-level language function issues an unsupported SVC, it results in a Txxx abend, where xxx is the hexadecimal SVC number. (for example, SVC 44 results in a T02C abend.)

It is recommended not to issue unsupported SVCs from within the DC/UCF address space. Improper use of operating system SVCs can cause severe performance problems, task abends, storage corruption, DC system abends, and even operating system failures.

Wherever possible, unsupported SVCs should be replaced with an equivalent DC service request. If this is not possible, you must either invoke the program in such a way that SVC screening is not in effect, or disable SVC screening for the unsupported SVCs.

SVC screening is only in effect for assembler programs invoked using a high-level language call function. If an assembler program is invoked in some other way, such as through a DC TRANSFER CONTROL verb, SVC screening is not in effect.

To disable SVC screening of unsupported SVCs, use the new SYSIDMS DISABLE_SVC_SCREEN parameter. This parameter should not be used to disable screening of the following SVCs that have DC service equivalents: 4, 5, 6, 7, 8, 9, 10, 11, 13, 19, 20, 24, 35, 48, 56, 60, 109, 120, and 122.

The following SYSIDMS parameter lets you control the screening of SVCs.

DISABLE_SVC_SCREEN=SVC-number

Specifies the number of an SVC for which screening is to be disabled.

Limits: 0–255

Disabling screening of an SVC allows it to be issued by a program executing within the DC/UCF address space.

The DISABLE_SVC_SCREEN parameter can be specified multiple times.

Note: Use this parameter with caution, since issuing unscreened SVCs within the DC/UCF system can degrade performance and result in abends. For more information about SVC screening, see DML Reference Guide for Assembler.