360 Assembly/360 Instructions/EX
EX - EXecute - Opcode X / Decimal
- BCTR R1,0
- EX R1,LABEL
- LABEL PACK PACKIT,0(L,R3)
- L will be replaced with last byte value of R1
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
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