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Learn how to easily assign a pointer to a custom section in ELF files using GCC in your embedded STM32 software.
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How to Assign a Pointer to a Custom Section with GCC in Embedded Software

Writing embedded software can often involve needing to manipulate custom sections in your program's binary, especially when working with tools like GNU Compiler Collection (GCC). One common question that arises is how to assign a pointer to a custom section that is added after compilation. In this guide, we’ll walk you through the steps to accomplish just that, particularly in STM32 projects.

Understanding the Problem

When working on your embedded projects, you might want to store specific data in a section separate from your program. Suppose you want to inject a piece of data into a new section (my_section) in an ELF file. Additionally, you'll need to create a pointer to access this data from your code.

For example, using the following code snippet, you may intend to point to an array defined within this custom section:

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Here, you’ll need to address how to properly define and access this section after compilation.

The Solution

Step 1: Defining Your Custom Section

Contrary to what you might think, you won’t need to use the objcopy --add-section command to achieve this. Instead, you can directly instruct GCC to place your data into a specific section using a special attribute. Here’s how you can do it:

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Step 2: Accessing the Section in Your Code

Next, once you've defined your array within the my_section, you can access the start and end of this section using the predefined linker symbols. The linker generates these symbols for you, which allows your code to understand where the section begins and ends. You can define pointers like this:

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Putting It All Together

Here is how your code would look when implemented fully:

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Step 3: Compiling Your Code

When you compile your my_data.cpp file with GCC, it will now place my_array in the specified my_section. You’ll also ensure that your build process correctly includes the linker flags to maintain these custom sections.

Conclusion

By following the steps outlined above, you can effectively assign a pointer to a custom section in your embedded software using GCC. This allows you to manage data in a more structured way, especially beneficial in lower-level programming where memory management is crucial.

Feel free to implement this approach in your STM32 projects and take advantage of organizing your data as needed while keeping your software efficient and effective. Happy coding!