How to Generate a Call Graph for C Code to Analyze Execution Paths?

Generating a Call Graph for C Code

This article explores techniques for creating a call graph for C code, particularly when attempting to identify all possible execution paths leading to a specific function.

Creating a Call Graph

To address this need, one approach is to leverage the LLVM optimization pipeline. This can be achieved by compiling the code with the -S and -emit-llvm flags, followed by the -analyze and -dot-callgraph options through the opt tool. For example:

$ clang++ -S -emit-llvm main1.cpp -o - | opt -analyze -dot-callgraph
$ dot -Tpng -ocallgraph.png callgraph.dot

This command generates a call graph that represents the potential execution paths, depicted as a visual diagram.

Customizing Call Graph Representation

In some cases, it may be beneficial to post-process the call graph to enhance readability. One method is to employ c filt to obtain unmangled function and class names. The following example demonstrates this process:

$ clang++ -S -emit-llvm main1.cpp -o - |
   opt -analyze -std-link-opts -dot-callgraph
$ cat callgraph.dot |
   c++filt |
   sed 's,>,\>,g; s,-\>,->,g; s,<,\<,g' |
   gawk '/external node/{id=}  != id' |
   dot -Tpng -ocallgraph.png    

By applying this modified graph, it becomes easier to identify the specific functions and classes involved in each path.

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