360 Assembly/360 Instructions/EX

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EX - EXecute - Opcode X / Decimal

Contents

FormatEdit

BCTR R1,0
EX R1,LABEL
LABEL PACK PACKIT,0(L,R3)
L will be replaced with last byte value of R1

OpcodeEdit

AvailabilityEdit

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

Purpose of InstructionEdit

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.

Typical UsageEdit

OperationEdit

Exceptions and FaultsEdit

  • 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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