Resolving BPF Helper Functions Compilation Issues in Ubuntu Using Clang and LLVM

Learn how to resolve issues while compiling eBPF programs in Ubuntu with Clang and LLVM, particularly concerning BPF helper functions and object file formats.
---
This video is based on the question https://stackoverflow.com/q/70360293/ asked by the user 'user786' ( https://stackoverflow.com/u/4808760/ ) and on the answer https://stackoverflow.com/a/70377082/ provided by the user 'Qeole' ( https://stackoverflow.com/u/3716552/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: compiling extended berkley packet filters program in ubuntu clang and llvm installed with libbpf also installed bt helper func not found& formar error

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Compiling Extended Berkeley Packet Filters Program in Ubuntu with Clang and LLVM

If you're working with Extended Berkeley Packet Filters (eBPF) in Ubuntu and you run into issues during the compilation of your program, you are not alone. Many developers encounter problems specifically when trying to compile eBPF programs using Clang and LLVM, particularly with BPF helper functions and object file formats. In this guide, we'll address these issues and guide you through the process step by step.

The Problem

You've set up your environment with essential tools including Clang, LLVM, kernel headers, and libbpf, but you're facing an error stating that some BPF helper functions are not found. Additionally, you received an "unrecognized format" message when trying to inspect the generated object file using llvm-objdump. This situation can be frustrating, especially if you want to get a simple eBPF program running in response to execve system calls.

Here’s a minimal version of the code you are trying to compile:

[[See Video to Reveal this Text or Code Snippet]]

Understanding the Error Messages

Missing BPF Helper Functions

The message regarding missing BPF helper functions usually indicates that the compiler cannot find the headers or that there is an issue with the include paths. The solution lies in ensuring that you correctly include the necessary headers.

Solution Steps:

Use Correct Header File: Instead of including bpf_helpers.h directly from the copied location, make sure you include it from the libbpf package installed on your system:

[[See Video to Reveal this Text or Code Snippet]]

This change ensures that the compiler correctly points to the installed library's headers rather than a potentially outdated or incorrect version.

Modify Your Loader Program: When loading your BPF program, also include the appropriate loader headers:

[[See Video to Reveal this Text or Code Snippet]]

Unrecognized Format in llvm-objdump

If you're running llvm-objdump -S ./one.o and see "unrecognized format", the issue is likely related to how you're compiling your program. It's important to ensure that you're using the right compilation flags.

Compilation Advice:

Compile with the Right Target: Make sure you specify the BPF target during compilation. Try using a command like the following:

[[See Video to Reveal this Text or Code Snippet]]

This command specifies that the output should be an object file designed for BPF, which helps prevent any unrecognized format issues.

Conclusion

By ensuring you have the correct header files and compile with appropriate flags, you can resolve the problems you're facing when compiling eBPF programs using Clang and LLVM on Ubuntu. Following these steps not only helps in addressing the current issues but also builds a solid foundation for your future eBPF projects. Should you encounter further issues, don't hesitate to refer back to this guide or seek additional resources in the eBPF community.

Remember that compiling BPF programs requires attention to detail, particularly with header files and compile options. Happy coding!

Видео Resolving BPF Helper Functions Compilation Issues in Ubuntu Using Clang and LLVM канала vlogize