Enhance Llgo Build: Implement -size Flag For Code Size Analysis

Are you working on embedded systems or bare-metal projects with Go and llgo? Do you need a quick way to understand the size of your compiled firmware? This proposal suggests adding a -size flag to llgo build, mirroring the functionality found in tinygo build. This enhancement will provide developers with crucial insights into code and data usage, making it easier to optimize firmware for flash and RAM budgets.

The Need for a -size Flag

When developing for embedded systems, every byte counts. Knowing the size of your .text, .data, and .bss sections is essential to ensure your firmware fits within the constraints of the target hardware. Currently, after llgo build completes, you're left with a compiled artifact, but little information about its size. To get this information, developers must manually run llvm-readelf --all and sift through the output—a tedious and time-consuming process. This proposal aims to streamline this process by integrating size analysis directly into the build process.

The proposed -size flag would address these challenges directly. By providing a clear and concise summary of code and data usage, developers can quickly identify areas for optimization. This feature aligns with the needs of embedded and bare-metal developers who require precise control over their firmware size. The implementation of this flag will significantly enhance the usability of llgo for resource-constrained environments.

Proposed Implementation: A Streamlined Approach

The implementation of the -size flag in llgo build involves several key steps. First, the llgo build command will accept the -size flag as an optional argument. This flag will accept values such as short (for a summary view, the default) and full (for a detailed llvm-readelf --all dump). After the linking step of the build process is complete, llgo will run llvm-readelf --all on the generated artifact. This will provide a comprehensive view of the ELF file's structure and contents.

Next, the implementation will parse the section table to aggregate sizes per ELF section. It will then organize these sizes by originating module, which could include the runtime, user packages, and third-party packages. The output will be formatted into a table similar to what tinygo build -size provides. This table will display the sizes of different sections (like .text, .rodata, .data, and .bss) and the total size for each module. The -size full option will output the summary table along with the raw llvm-readelf --all data, allowing developers to dive deep into symbols and sections without extra steps.

Anticipated Output

The formatted table is designed to provide quick and clear insights into the code and data distribution. Here’s an example of what the output might look like:

   module        text    rodata    data     bss   total
   runtime       10.5k     1.2k       0     512   12.2k
   machine       3.4k        0       0       0    3.4k
   user/main     6.7k       512     32     128    7.4k

This output format will make it easy to see which parts of your code are contributing the most to the overall size of the firmware. This information is invaluable for optimization.

Technical Details: Making it Happen

The technical aspects of implementing the -size flag involve several considerations. The llgo build driver already knows the location of the compiled artifact, making it easier to invoke llvm-readelf. A helper function within the internal/build package can handle the invocation of llvm-readelf, using the same toolchain discovery mechanism (LLGO_LLVM_BIN or similar) used for clang and llvm-link. This ensures that the correct version of llvm-readelf is used. Furthermore, the tinygo project exposes a size analysis package that can serve as a reference. By documenting the format of the output, the community can extend and refine the feature over time.

Addressing the Challenge of Temporary Artifacts

If the -o flag (specifying the output file) is not provided, the temporary artifact should be written to disk. This is a crucial step because llvm-readelf needs a file to inspect. This ensures that the size analysis can be performed even when a specific output file is not explicitly defined. The temporary artifact is cleaned up after llvm-readelf has finished its analysis.

Benefits and Future Enhancements

The immediate benefit of implementing the -size flag is the ability to quickly assess the size of your firmware. This reduces the time and effort needed to optimize code for embedded systems. This feature also lowers the barrier to entry for developers new to llgo, as it provides a familiar workflow for those already using tinygo. By mirroring the functionality of tinygo, the -size flag reduces friction for developers switching between toolchains.

Future Enhancements

The -size flag can be extended with further enhancements. In the future, a diff mode (--size diff <old.elf>) could be added to compare the size of different builds. Percentage totals, and CSV/JSON output for use in continuous integration (CI) enforcement, are also possibilities. These enhancements would make the -size flag even more powerful and versatile.

Conclusion: Improving llgo for Embedded Development

The -size flag is a valuable addition to llgo build, especially for embedded and bare-metal developers. By providing immediate feedback on code and data usage, it streamlines the optimization process. This feature aligns with the needs of the Go community and provides developers with the tools to build efficient and resource-conscious firmware. The implementation will be straightforward, leveraging existing infrastructure and drawing inspiration from tinygo. This proposal helps make llgo a more powerful tool for embedded development.

For further reading on embedded systems and code optimization, please visit Embedded Systems Programming.