|

|  How to resolve symbol resolution issues in GNU Linker for embedded projects?

How to resolve symbol resolution issues in GNU Linker for embedded projects?

October 14, 2024

Discover effective solutions to tackle symbol resolution issues in GNU Linker for embedded projects. Tailored for firmware developers seeking streamlined guidance.

How to resolve symbol resolution issues in GNU Linker for embedded projects?

 

Understanding the Context
 

In embedded projects, symbol resolution issues can become a significant hurdle during the linking process using the GNU Linker (ld). These issues typically arise due to undefined references, multiple definitions, or version mismatches. Addressing these challenges requires a thorough understanding of how the linker operates and how it uses symbol tables to resolve references across object files, libraries, and linker scripts.

 

Common Causes of Symbol Resolution Issues
 

  • Undefined References: When a symbol used in one file does not have a corresponding definition available during linking.

  • Multiple Definitions: Occurs when the same symbol is defined in multiple files, resulting in ambiguity for the linker.

  • Version Mismatches: Different symbol versions may exist, particularly in large projects or when integrating with third-party libraries, causing conflicts.

 

Strategies for Resolving Symbol Resolution Issues
 

  • Stub Symbols for Undefined References

    One way to handle undefined references during development is to define stub functions in a separate object file. These stubs allow the linker to resolve symbols without requiring full implementations at that stage. For example:

    ```c
    // stub.c
    #include <stdio.h>

    void missingFunction() {
    // Stub implementation
    printf("Missing function stub called.\n");
    }
    ```

    Compile stub.c and include it during linking to resolve the missing symbol.

     

  • Using Linker Scripts for Symbol Control

    Linker scripts can provide fine-grained control over symbol resolution. By explicitly specifying memory regions and symbol locations, they can resolve ambiguities in symbol definition:

    ```ld
    /_ custom.ld _/
    SECTIONS {
    .text : {
    *(.text)
    _(.text._)
    }
    .data : {
    *(.data)
    _(.data._)
    }
    /_ Additional custom sections can be defined as needed _/
    }
    ```

    Configure the linker with a custom script using the -T option:

    ```bash
    ld -T custom.ld -o output.elf input.o
    ```

     

  • Apply Weak Symbols

Weak symbols let you define a default implementation that can be overridden. This technique is useful when designing libraries or systems allowing optional, user-provided implementations. In C, you define a symbol as weak like this:

```c
// default_impl.c
**attribute**((weak)) void optionalFunction() {
// Default implementation
}
```

Any strong definition of optionalFunction will take precedence, providing flexibility in symbol resolution.

 

  • Examining Linker Map Files

    To troubleshoot symbol resolution issues, generate and examine the linker map file. It provides a detailed symbol list, addresses, and references, aiding the identification of unresolved references:

    ```bash
    ld -Map=output.map -o output.elf input.o
    ```

    Analyze output.map to pinpoint where symbols are defined and referenced, identifying discrepancies.

     

  • Order of Libraries and Files

    The order in which object files and libraries are specified can affect resolution, particularly with static libraries. Ensure libraries appear after object files:

    ```bash
    ld input.o -L/path/to/libs -lmylib
    ```

    Adjusting the order can sometimes resolve unexpected undefined references.

     

Advanced Techniques for Complex Scenarios
 

  • Symbol Aliasing

    When facing symbol conflicts due to multiple definitions, aliasing can resolve issues by distinguishing conflicting symbols. For instance:

    ```c
    // implementation.c
    void __real_conflictFunction();
    void __wrap_conflictFunction() {
    // Wrapper implementation
    __real_conflictFunction();
    }
    ```

    Use linker flags to alias the symbol:

    ```bash
    ld --wrap=conflictFunction -o output.elf input.o
    ```

     

  • Selective Linking with --whole-archive

    If specific files or libraries might otherwise be discarded, forcefully include them using --whole-archive:

    ```bash
    ld --whole-archive -lmyLibrary --no-whole-archive -o output.elf input.o
    ```

    This guarantees all symbols within the specified archive are included.

By applying these strategies and techniques, you can systematically resolve symbol resolution issues in embedded projects using the GNU Linker, leading to successful and efficient firmware builds.

Pre-order Friend AI Necklace

Pre-Order Friend Dev Kit

Open-source AI wearable
Build using the power of recall

Order Now

OMI AI PLATFORM
Remember Every Moment,
Talk to AI and Get Feedback

Omi Necklace

The #1 Open Source AI necklace: Experiment with how you capture and manage conversations.

Build and test with your own Omi Dev Kit 2.

Omi App

Fully Open-Source AI wearable app: build and use reminders, meeting summaries, task suggestions and more. All in one simple app.

Github →

Join the #1 open-source AI wearable community

Build faster and better with 3900+ community members on Omi Discord

Participate in hackathons to expand the Omi platform and win prizes

Participate in hackathons to expand the Omi platform and win prizes

Get cash bounties, free Omi devices and priority access by taking part in community activities

Join our Discord → 

OMI NECKLACE + OMI APP
First & only open-source AI wearable platform

a person looks into the phone with an app for AI Necklace, looking at notes Friend AI Wearable recorded a person looks into the phone with an app for AI Necklace, looking at notes Friend AI Wearable recorded
a person looks into the phone with an app for AI Necklace, looking at notes Friend AI Wearable recorded a person looks into the phone with an app for AI Necklace, looking at notes Friend AI Wearable recorded
online meeting with AI Wearable, showcasing how it works and helps online meeting with AI Wearable, showcasing how it works and helps
online meeting with AI Wearable, showcasing how it works and helps online meeting with AI Wearable, showcasing how it works and helps
App for Friend AI Necklace, showing notes and topics AI Necklace recorded App for Friend AI Necklace, showing notes and topics AI Necklace recorded
App for Friend AI Necklace, showing notes and topics AI Necklace recorded App for Friend AI Necklace, showing notes and topics AI Necklace recorded

OMI NECKLACE: DEV KIT
Order your Omi Dev Kit 2 now and create your use cases

Omi Dev Kit 2

Endless customization

OMI DEV KIT 2

$69.99

Perfect for developers and tech enthusiasts who want to start creating immediately.

Has 64gb of on-board memory, a speaker, vibration and a programmable button.

Comes fully assembled, doesn't require technical skills to set up.

 

IMPORTANT: On backorder. Shipping end of November 2024.

Learn more

Omi Dev Kit 2: build at a new level

Key Specs

OMI DEV KIT

OMI DEV KIT 2

Microphone

Yes

Yes

Battery

4 days (250mAH)

2 days (250mAH)

On-board memory (works without phone)

No

Yes

Speaker

No

Yes

Programmable button

No

Yes

Estimated Delivery 

-

1 week

What people say

“Helping with MEMORY,

COMMUNICATION

with business/life partner,

capturing IDEAS, and solving for

a hearing CHALLENGE."

Nathan Sudds

“I wish I had this device

last summer

to RECORD

A CONVERSATION."

Chris Y.

“Fixed my ADHD and

helped me stay

organized."

David Nigh

OMI NECKLACE: DEV KIT
Take your brain to the next level

LATEST NEWS
Follow and be first in the know

Latest news
FOLLOW AND BE FIRST IN THE KNOW

San Francisco

team@basedhardware.com
Title

Company

About

Careers

Invest
Title

Products

Omi Dev Kit 2

Openglass

Other

App marketplace

Affiliate

Privacy

Customizations

Discord

Docs

Help