Solving the Linker Problem while Retargeting Newlib with a Static Library

Are you tired of banging your head against the wall, trying to retarget Newlib with a static library, only to be met with frustrating linker errors? Fear not, dear developer! In this article, we’ll embark on a thrilling adventure to conquer the linker problem and emerge victorious.

What’s the Linker Problem, Anyway?

Before we dive into the solution, let’s first understand the issue at hand. When you try to retarget Newlib with a static library, the linker throws a tantrum, complaining about undefined references to symbols like `_malloc_r`, `_free_r`, or `_realloc_r`. This is because the static library wasn’t built with the correct settings, causing the linker to freak out.

Preparing the Battlefield ( Err, Your Development Environment)

To tackle this problema, you’ll need:

• A C/C++ compiler (e.g., GCC)
• A linker (e.g., GNU ld)
• Newlib (the standard library for embedded systems)
• A static library (the one you want to retarget)
• A text editor or IDE (for modifying configuration files)

Step 1: Configure Newlib

Before we start retargeting, we need to configure Newlib to play nicely with our static library. Create a new file called `newlib.cfg` with the following contents:

<TARGET>
LIBGCC := ../../../lib/gcc/$(TARGET)/$(VERSION)/libgcc.a
LIBC := ../../../newlib/lib/libc.a
LIBM := ../../../newlib/lib/libm.a
</TARGET>

This configuration file tells Newlib to use the correct libraries for our target platform. Adjust the paths as needed to match your Newlib installation.

Step 2: Create a Custom Linker Script

The default linker script provided by Newlib doesn’t know about our static library. Let’s create a custom script to guide the linker. Create a new file called `linker.ld` with the following contents:

MEMORY
{
  ram : ORIGIN = 0x00000000, LENGTH = 0x00100000
}

SECTIONS
{
  .text :
  {
    *(.text)
  } > ram

  .rodata :
  {
    *(.rodata)
  } > ram

  .data :
  {
    *(.data)
  } > ram

  .bss :
  {
    *(.bss)
  } > ram
}

LIBGCC = ../../../lib/gcc/$(TARGET)/$(VERSION)/libgcc.a
LIBC = ../../../newlib/lib/libc.a
LIBM = ../../../newlib/lib/libm.a
STATIC_LIB = ../../../path/to/your/static/library.a

This linker script defines the memory layout for our target platform and specifies the libraries to include, including our static library. Update the paths to match your environment.

Step 3: Compile Your Static Library (Again)

Recompile your static library using the following command:

gcc -c -o your_file.o your_file.c -I ../../../newlib/include

This ensures that your static library is built with the correct Newlib include paths.

Step 4: Create a Newlib-Retargeted Static Library

Now it’s time to retarget your static library with Newlib. Use the following command:

gcc -nostdlib -o newlib_static_library.a your_file.o ../../../newlib/lib/libc.a ../../../newlib/lib/libm.a ../../../lib/gcc/$(TARGET)/$(VERSION)/libgcc.a -T linker.ld

This command builds a new static library, `newlib_static_library.a`, which is retargeted to use Newlib.

Step 5: Verify the Linker Problem is Gone

Compile a simple test program using the new static library:

gcc -o test test.c newlib_static_library.a -T linker.ld

If everything went smoothly, the linker should no longer complain about undefined references to Newlib symbols.

Troubleshooting Common Issues

Issue 1: Symbol Not Found

If the linker still complains about undefined symbols, double-check that:

• You’ve included all necessary libraries in the linker command
• The library paths are correct
• The static library was rebuilt with the correct Newlib include paths

Issue 2: Multiple Definitions

If the linker complains about multiple definitions of symbols, ensure that:

• You’ve used the `-nostdlib` flag when building the new static library
• You’ve specified the correct libraries in the linker command

Conclusion

Victory is yours! With these steps, you’ve successfully retargeted your static library with Newlib, banishing the linker problem to the depths of debugging hell. Pat yourself on the back, dear developer, and bask in the glory of your triumph.

Important Files	Description
newlib.cfg	Newlib configuration file
linker.ld	Custom linker script
newlib_static_library.a	Newlib-retargeted static library

Remember, when facing the linker problem, stay calm, and methodically work through each step. With patience and persistence, you’ll conquer even the most stubborn linker errors.

1. Share your experiences and tips in the comments below!
2. Check out our other articles on embedded systems development
3. Subscribe to our newsletter for more coding adventures

Frequently Asked Question

If you’re struggling with linker problems while retargeting newlib with a static library, you’re not alone. Here are some of the most commonly asked questions and answers to help you overcome these issues.