Description: Control Flow Graph (CFG)

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CodeSonar^® 9.2p0

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Description: Control Flow Graph (CFG)

CodeSonar can construct control flow graphs (CFGs). With these graphs enabled, you can navigate through a program's control flow structure as well as its dependence structure.

Overview
API Functionality
Example CFGs
Links

Overview

The sequential flow of control through the program is represented by control-flow edges (CFG_EDGE) between points (PDG_VERTEX), a structure known as a control flow graph, or CFG for short.

For example, consider the following example program and its corresponding CFG (with printf() calls collapsed to 'print' points).

/* Return a+b */
static int add(int a, int b){
    return a + b;
}

/* Sum 0 through 10. */
void main()
{
    int sum, i;
    sum = 0;
    i = 1;
    while ( i<11 ) {
        sum = add(sum, i);
        i = add(i, 1);
    }
    printf("sum = %d\n", sum);
    printf("i = %d\n", i);
}

API Functionality

Intraprocedural and Interprocedural CFGs

Each function is associated with an intraprocedural CFG that models control flow between points strictly within the function based on the assumption that all function calls are atomic operations.

The inter-procedural CFG is a single graph that models the control flow between points in the entire project.

Control-Flow Edge

Edges in the CFG are called control flow edges.

Each control-flow edge is labeled: an edge leaving a conditional is labeled either True or False; an edge leaving a switch is labeled with generated strings representing the case; an unconditional edge is labeled True.
Control passes into a function from the last actual-in parameter to be evaluated, and returns from the function's exit point to the next sequential instruction after the call site. The CFG successor of every return statement in a function is the function's unique program point of kind exit.
The order of evaluation of actual parameters is explicit in the CFG, even though this order is not defined by the ANSI C standard, and is compiler specific.
- Evaluation is right-to-left (this matches the evaluation order of most popular compilers).
- Control flows through actual-in parameters, which in general may contain expressions that must be evaluated, and through actual-out parameters, which represent the assignment of the return value to a temporary variable. Control does not flow through formal parameters.

Language	CFG Edges from a point		Types
Language	Intraprocedural	Interprocedural	CFG Edge	CFG Edge Set
C++	point::cfg_targets()	point::cfg_inter_targets()	typedef cfg_edge	class cfg_edge_set
Python	point.cfg_targets()	point.cfg_inter_targets()	pair (point, edge_label)	class cfg_edge_set
C	cs_pdg_vertex_cfg_targets()	cs_pdg_vertex_cfg_inter_targets()	typedef cs_cfg_edge	typedef cs_cfg_edge_set, typedef cs_const_cfg_edge_set

Example CFGs

Example C/C++ CFGs are provided in section Control Flow Graphs for C/C++ Programs.

Description: Control Flow Graph (CFG)

Overview

API Functionality

Intraprocedural and Interprocedural CFGs

Control-Flow Edge

Example CFGs

Links