> For the complete documentation index, see [llms.txt](https://kmanu225.gitbook.io/cs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://kmanu225.gitbook.io/cs/sandbox/cross-compilation.md). # Cross-Compilation Some days, you realize just how much you take a simple `curl` command for granted. Recently, during a professional assignment, I faced a "hardened" ARM/GNU Linux target. The setup? A system stripped to its bare essentials: no package manager, no compiler, and—most importantly—no `curl`. My challenge: initiate HTTPS requests on a machine with virtually no network tools. This is the story of my deep dive into the world of cross-compilation. ### The Context: From WSL to ARM My workstation was a WSL2 environment (**x86\_64**). My target? An **armv7l** processor. Compiling directly on the target was impossible, and waiting for the systems team to provide tools or info would have taken weeks. It was just me and my terminal. ### The "All-in-One" Strategy (Static Binary) Since I had little visibility into which libraries were available on the target, I made a radical choice: **static linking**. Instead of relying on shared libraries (`.so`) on the destination, I decided to bake all dependencies directly into the `curl` executable. ### Choosing Lightness: Musl The standard `glibc` is often too bloated or complex for pure static linking. That’s where **musl libc** comes in. It is a lightweight alternative optimized for static binaries. It was the missing piece of the puzzle to ensure my binary would run flawlessly on a minimalist kernel. ### The Crash Test: qemu-arm-static Compiling is great, but testing without constant back-and-forth with the target is better. Thanks to `qemu-arm-static`, I was able to emulate and run my ARM binary directly within my WSL terminal. I regretted missing this step during my first attempts. In fact, I could not access the target whenever I wanted. Once I saw the `curl` help menu pop up on my x86 host, I knew I had won. ### The Recipe The final configuration can be found on my GitHub: [compliation-recipe/x86\_64-to-arm/curl at main · kmanu225/compliation-recipe](https://github.com/kmanu225/compliation-recipe/tree/main/x86_64-to-arm/curl). If I had to keep one thing in mind when dealing with cross-compilation, it is that you need to properly characterize the target before taking any action. ### Glossary For those looking to demystify the technical jargon used above: * **Architecture (ARM vs x86):** The processor's physical "language." A program compiled for a PC (x86) is unreadable by a mobile or embedded processor (ARM). * **libc:** The fundamental C library. It acts as the bridge between your code and the Linux kernel (e.g., opening a file). * [**musl libc**](https://musl.libc.org/)**:** A lightweight, fast, and simple implementation of the C standard library. * **Cross-compilation:** The process of compiling a program on Architecture A to run on Architecture B. * **Static vs. Dynamic Linking:** * **Dynamic:** The program calls external files at runtime. * **Static:** The program bundles everything into a single file. More robust but larger (my `curl` binary went from a few KB to several MB). * **eabihf (Embedded Application Binary Interface Hard Float):** A calling convention indicating the processor uses its hardware unit for floating-point math (faster). * **CMake vs Make:** `Make` executes build scripts. `CMake` is a higher-level tool that generates those scripts for you. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://kmanu225.gitbook.io/cs/sandbox/cross-compilation.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.