Understanding the Error: "undefined reference to __aeabi_memcpy"
When compiling embedded C code for ARM architectures, encountering the error "undefined reference to __aeabi_memcpy" usually indicates that the linker cannot find a definition for the __aeabi_memcpy function. This error is common in firmware development and can be perplexing if you're unaware of what __aeabi_memcpy signifies.
What is __aeabi_memcpy?
__aeabi_memcpy is a part of the ARM runtime library. Embedded code often relies on specific library functions for tasks like memory operations, especially when handling data in low-level programming. This particular function is used for memory copying tasks.
Common Causes of the Error
- Missing Link to the ARM Runtime Library: If the ARM runtime libraries are not included in your build process, the linker will not find `__aeabi_memcpy`, resulting in the undefined reference error.
- Incorrect Compiler Flags: Compiler settings might not be correctly configured to include the necessary libraries. This can happen if the flags for linking the ARM standard libraries are missing or incorrect.
- Custom Implementations: A custom memory operation function intended to replace or override the default might be declared but not defined, or defined incorrectly.
- Cross-Compiling Issues: Using the wrong toolchain (for example, building with a non-ARM-specific compiler) can also result in this error since the function is ARM-specific.
How to Resolve the Error
- Ensure Correct Linking of ARM Libraries: Include the correct ARM runtime libraries during the linking stage. This might mean setting the linker path properly and ensuring that the flags like `-lc` or specific ARM toolchain flags are used.
arm-none-eabi-gcc -o output.elf main.o -lc
<li><b>Verify Compiler and Linker Flags:</b> Double-check your makefile or your build configuration to ensure that you're using the correct compiler and linker flags. Often, flags like `-specs=nosys.specs` are used for bare-metal ARM projects.</li>
<li><b>Implement Custom Versions if Necessary:</b> If overriding `__aeabi_memcpy`, make sure the custom function is properly implemented, declared, and defined. For example:
void __aeabi_memcpy(void *dst, const void *src, size_t n) {
char *d = dst;
const char *s = src;
while (n--) {
*d++ = *s++;
}
}
<li><b>Use the Correct Toolchain:</b> If using an ARM-specific compiler, make sure it is the right one for your architecture version and that it supports the embedded system's requirements.</li>
Best Practices
- Use the Latest Toolchain: Ensure you're using the most up-to-date and appropriate toolchain for your ARM architecture.
- Read the Compiler Documentation: ARM compiler documentation will have specifics on which runtime libraries need to be linked and how.
- Toolchain Configuration: Configure paths properly to ensure your compiler can access ARM runtime libraries.
- Consider Using a Build System: If not already using one, consider adopting a build system like CMake, which can streamline the inclusion of libraries and proper flags.
By addressing these factors, you should be able to resolve the "undefined reference to __aeabi_memcpy" error and ensure that your firmware application links successfully and functions correctly.
