prongC: A Static Analysis Tool That Helps You Detect C Shared Data Accesses

If you’ve ever stared at a large C codebase wondering whether two function calls touch the same shared state, you know the pain. Manual code review is error-prone, and full program analysis can be overkill. prongC was built to solve exactly this problem. It’s a lightweight static analysis tool that detects shared variable accesses between function calls without requiring whole-program analysis.

The Problem It Solves

Consider this scenario: you have two function calls in your code:
foo(arg1, arg2, shared_arg);
bar(shared_arg, arg3);

Can you safely reorder them? Do they both read or modify the same variables? prongC gives you a definitive answer by tracing how each argument flows through the function bodies.

Key features

• No whole-program analysis – prongC only works with the functions and files you specify
• Individual parameter and global tracing – prongC can identify all variable accesses to globals or parameters you specify individually
• Compile database support – works seamlessly with compile_commands.json
• Multithreaded parsing – parse C files faster with -j option

Usage

You tell prongC which files to analyze and which function calls to examine:

prongc --files="file1.c,file2.c" \
       --functions="foo(arg1, arg2, shared_arg);bar(shared_arg, arg3)" \
       -j8

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The tool traces how each argument is used through the program and reports any overlaps.

You can also trace individual parameters of functions or globals by name:

prongc --files="file.c" \
       --functions="foo(arg1)" \
       --trace="foo@arg1"

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Useful for

• Finding hidden variable access overlaps
• Verifying function call reordering safety
• Investigating side effects in legacy C code you’re maintaining
• Exploring data dependencies across multiple files
• Undestanding unfamiliar codebases faster by uncovering data relationships

Output example

-------------------
Variable overlap:
foo(char *arg1, int arg2, bool shared_arg) → file1.c, line: 639, col: 6  │ READ : shared_arg
        if (shared_arg) {
            ^
bar(bool shared_arg, size_t arg3) → file1.c, line: 699, col: 25  │ READ : shared_arg
        var = shared_arg;
              ^
-------------------

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Or for individual variable tracing

Input example:

prongc --files="file.c" \
       --functions="foo(arg1, arg2, arg3)" \
       --trace="foo@arg1"

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Output:

-------------------
Tracing foo@arg1:
foo(char *arg1, int arg2, bool arg3) → file.c, line: 540, col: 9 │ READ : arg1
        local = arg1;
                ^
-------------------

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