Additional P-CODE Operations
Prev |  | Next

## Additional P-CODE Operations

The following opcodes are not generated as part of the raw translation of a machine instruction into p-code operations, so none of them can be used in a processor specification. But, they may be introduced at a later stage by various analysis algorithms.

### MULTIEQUAL

Parameters | Description
input0 |  | Varnode to merge from first basic block.
input1 |  | Varnode to merge from second basic block.
[...] |  | Varnodes to merge from additional basic blocks.
output |  | Merged varnode for basic block containing op.
Semantic statement |
| Cannot be explicitly coded.

This operation represents a copy from one or more possible locations. From the compiler theory concept of Static Single Assignment form, this is a phi-node. Each input corresponds to a control-flow path flowing into the basic block containing the MULTIEQUAL. The operator copies a particular input into the output varnode depending on what path was last executed. All inputs and outputs must be the same size.

### INDIRECT

Parameters | Description
input0 |  | Varnode on which output may depend.
input1 | (special) | Code iop of instruction causing effect.
output |  | Varnode containing result of effect.
Semantic statement |
| Cannot be explicitly coded.

An INDIRECT operator copies input0 into output, but the value may be altered in an indirect way by the operation referred to by input1. The varnode input1 is not part of the machine state but is really an internal reference to a specific p-code operator that may be affecting the value of the output varnode. A special address space indicates input1's use as an internal reference encoding. An INDIRECT op is a placeholder for possible indirect effects (such as pointer aliasing or missing code) when data-flow algorithms do not have enough information to follow the data-flow directly. Like the MULTIEQUAL, this op is used for generating Static Single Assignment form.

A constant varnode (zero) for input0 is used by analysis to indicate that the output of the INDIRECT is produced solely by the p-code operation producing the indirect effect, and there is no possibility that the value existing prior to the operation was used or preserved.

### PTRADD

Parameters | Description
input0 |  | Varnode containing pointer to an array.
input1 |  | Varnode containing integer index.
input2 | (constant) | Constant varnode indicating element size.
output |  | Varnode result containing pointer to indexed array entry.
Semantic statement |
| Cannot be explicitly coded.

This operator serves as a more compact representation of the pointer calculation, input0 + input1 * input2, but also indicates explicitly that input0 is a reference to an array data-type. Input0 is a pointer to the beginning of the array, input1 is an index into the array, and input2 is a constant indicating the size of an element in the array. As an operation, PTRADD produces the pointer value of the element at the indicated index in the array and stores it in output.

### PTRSUB

Parameters | Description
input0 |  | Varnode containing pointer to structure.
input1 |  | Varnode containing integer offset to a subcomponent.
output |  | Varnode result containing pointer to the subcomponent.
Semantic statement |
| Cannot be explicitly coded.

A PTRSUB performs the simple pointer calculation, input0 + input1, but also indicates explicitly that input0 is a reference to a structured data-type and one of its subcomponents is being accessed. Input0 is a pointer to the beginning of the structure, and input1 is a byte offset to the subcomponent. As an operation, PTRSUB produces a pointer to the subcomponent and stores it in output.

### CAST

Parameters | Description
input0 |  | Varnode containing value to be copied.
output |  | Varnode result of copy.
Semantic statement |
| Cannot be explicitly coded.

A CAST performs identically to the COPY operator but also indicates that there is a forced change in the data-types associated with the varnodes at this point in the code. The value input0 is strictly copied into output; it is not a conversion cast. This operator is intended specifically for when the value doesn't change but its interpretation as a data-type changes at this point.

Prev |  | Next
Pseudo P-CODE Operations | Home | Syntax Reference