360 Assembly/360 Instructions/EX

EX - EXecute - Opcode X / Decimal

Format

BCTR R1,0

EX R1,LABEL

LABEL PACK PACKIT,0(L,R3)

L will be replaced with last byte value of R1

Availability

The EX instruction is available on all models, 360, 370 and z/System.

Purpose of Instruction

The EX instruction is used to allow a program to modify itself in order to change certain arguments of other instructions without acrually modifying the program's code. One use could be to move a string of 256 bytes or less, by executing an MVC instruction where the EX instruction changes the length value in that instruction.

Exceptions and Faults

• If the target instruction is itself an EX instruction, an Execute Exception occurs
• If the target instruction is not on an even address, an Address Exception occurs
• If the target instruction does not contain a valid opcode, an Operation Exception occurs
• If the target instruction is a privileged instruction, a Protect Violate exception occurs unless this task has the privileged bit in the PSW set
• If the instruction to be executed has an exception, that exception will be thrown