strip-simplifier

This script is designed to simplify the process of partially stripping an executable by removing specific global variables and functions. It offers a flexible, error-checked solution that can be easily integrated into your build or testing workflow.

Features

• Selective Symbol Stripping: Remove only the specified symbols (functions and/or global variables) from your executable using strip and objcopy.

• Interactive Mode: If no symbol files are provided, the script can prompt you to input specific symbols to strip interactively.

• Complete Strip Fallback: If no symbol lists are provided and interactive mode isn't enabled, the script will automatically perform a full strip of the executable.

• Error Handling: The script checks the outcome of every command (such as cp, strip, objcopy, and mv) and exits with a clear error message if something goes wrong.

• Backup Creation: A backup of the original executable is created before any modifications, ensuring you can always revert if needed.

• Backup restoration: The backup created from the script gets restored in order to revert all the modifications made.

• Command-Line Help: Detailed help is available via the -h option, which explains how to use the script and its various options.

Usage

To run the script, you must provide the executable file you want to strip. Optionally, you can also specify files that list the functions and/or global variables to be removed.

Command-Line Options

• -e executable (Required) Specifies the name (or path) of the executable to be processed.

• -f functions_file (Optional) A file containing the names of functions to be stripped from the executable.

• -g globals_file (Optional) A file containing the names of global variables to be stripped from the executable.

• -r (Optional) Restore the previously made backup executable in order to revert the strip operation. If it does not find a *.backup file in the current folder it throws an error message.

• -y (Optional) Enable interactive mode. If no symbol files are provided, the script will prompt you to input specific symbols to strip. If not used and no symbol files are provided, a full strip will be performed.

• -h Displays a help message detailing the usage of the script.

Examples

1. Selective Strip:

   If you have two files, functions.txt and globals.txt, listing the symbols you want to remove:

   ./strip-simplifier.sh -e my_executable -f functions.txt -g globals.txt

2. Strip Only Functions:

   ./strip-simplifier.sh -e my_executable -f functions.txt

3. Strip Only Globals:

   ./strip-simplifier.sh -e my_executable -g globals.txt

4. Interactive Mode (No Symbol Files):

   ./strip-simplifier.sh -e my_executable -y

5. Full Strip (No Symbol Files Provided):

   ./strip-simplifier.sh -e my_executable

6. Restore the executable

    ./strip-simplifier.sh -e my_executable -r

How to Test

1. Compile the Example:
   Compile the provided example.c with debugging symbols:

   gcc -g -o example example.c

2. Run the Script:
   Use the provided strip-simplifier.sh script along with globals.txt and functions.txt to remove the specified symbols:

   ./strip-simplifier.sh -e example -g globals.txt -f functions.txt

3. Verify the Result:
   Check the remaining symbols using nm:

   nm example | grep -E "global_var1|global_var2|function_to_strip|another_function_to_strip"

   You should see that the functions defined in the regex are not present, while if you use nm example | grep function_to_keep you will see that function_to_keep is still present, while the symbols listed in the globals and functions files have been removed.

4. Restore the backup: You can restore the backup by doing:

    ./strip-simplifier.sh -e example -r

5. Verify the backup: If you now check the example executable:

    nm example | grep -E "global_var1|global_var2|function_to_strip|another_function_to_strip"
   

   You should have an output like the following:

    000000000000119d T another_function_to_strip
    0000000000001169 T function_to_strip
    0000000000004010 D global_var1
    0000000000004014 D global_var2
   

   Which means that we correctly restored the backup from the stripped file.

Technical Details

The script utilizes both strip and objcopy to remove symbols. This dual approach ensures a higher level of confidence that the specified symbols are removed from the executable. It uses nm to display the symbols before and after the stripping process, which helps in verifying the changes.

Error Handling

Each critical operation (like copying the executable, stripping symbols, and renaming temporary files) is wrapped in a function that checks the command's exit status. If any command fails, the script outputs an error message and terminates, preventing further modifications on a potentially unstable binary.

Backup & Recovery

Before any modifications are made, the script creates a backup of the original executable by appending .backup to its name. This safeguard ensures that you can always revert to the original version if the strip operation does not yield the expected result.

Future Considerations

While the script has been significantly improved with interactive mode and backup restoration, there are still ideas for further enhancements:

• Interactive Mode: Prompt the user to decide on stripping symbols if no files are provided.
• Automatic Symbol Detection: Analyze the output of tools like nm or readelf to attempt an automatic distinction between library symbols and user-defined symbols. Note that this is challenging—especially for static executables—and might lead to false positives or negatives.
• Logging: Create a detailed log file that tracks every step and command output for troubleshooting purposes.
• Backup Restoration: An option to automatically restore the backup if the stripping process fails or if the user wishes to revert the changes.
• Symbol Pattern Matching: Add support for stripping symbols using pattern matching or regular expressions.
• Symbol Type Filtering: Add options to strip specific types of symbols (e.g., only strip data symbols or only strip function symbols).

Contributing

Contributions are welcome! If you have ideas for new features, improvements, or bug fixes, please open an issue or submit a pull request. Collaboration is encouraged to make this tool even more robust and user-friendly.

License

Distributed under the MIT License. See the LICENSE file for more details.