Understanding the `objcopy` Command (with examples)

objcopy is a versatile command-line utility available in Unix-like operating systems, primarily used in programming and software development contexts. It serves the purpose of copying and transforming object files. With objcopy, developers can manipulate object files in various ways, such as converting them between different formats, stripping unnecessary information, and copying specific sections of data. The utility comes in handy for managing binary files during the build or distribution processes. Below are some specific use cases demonstrating the power and flexibility of the objcopy command.

Use case 1: Copy data to another file

Code:

objcopy path/to/source_file path/to/target_file

Motivation:

Copying the contents of an object file to another file is a straightforward application of objcopy, often used for backup purposes or when you need to modify a copy of the file while preserving the original. This operation guarantees the integrity and consistency of data during software development or deployment.

Explanation:

• path/to/source_file: Specifies the original object file whose contents you want to copy.
• path/to/target_file: Indicates the new or target file where the contents will be copied.

Example Output:

The command copies the entire content of the source file to the target file, creating an identical duplicate. No output is generally shown unless an error occurs.

Use case 2: Translate object files from one format to another

Code:

objcopy --input-target=input_format --output-target=output_format path/to/source_file path/to/target_file

Motivation:

Translating object files between different formats is often necessary when working with cross-platform development. Developers need to generate files compatible with various systems or tools, allowing shared codebases to be used efficiently across different environments.

Explanation:

• --input-target=input_format: Indicates the format of the source file. Common formats include ELF, COFF, and PE.
• --output-target=output_format: Specifies the desired format for the target file.
• path/to/source_file: The original file to be converted.
• path/to/target_file: The destination file receiving the converted object.

Example Output:

Typically, there is no visual output unless an error or conversion issue occurs. The process results in a new object file conforming to the specified output format.

Use case 3: Strip all symbol information from the file

Code:

objcopy --strip-all path/to/source_file path/to/target_file

Motivation:

Stripping all symbol information from an object file greatly reduces its size, making it beneficial for releasing production binaries where debugging information is unnecessary. Smaller file sizes lead to quicker deployment and resource-efficient distribution.

Explanation:

• --strip-all: This flag directs objcopy to remove all symbol information from the object file, including debugging and other symbolic data.
• path/to/source_file: The object file from which information will be stripped.
• path/to/target_file: The resulting file with reduced content size.

Example Output:

Post-execution, the target file is noticeably smaller, devoid of symbolic information, thus optimizing for performance and obfuscation purposes.

Use case 4: Strip debugging information from the file

Code:

objcopy --strip-debug path/to/source_file path/to/target_file

Motivation:

While developing software, debug symbols are useful for identifying errors and performance bottlenecks. However, they are unnecessary in final production releases. Stripping debug information enhances security by preventing reverse-engineering and reducing the file size.

Explanation:

• --strip-debug: This option removes only debugging-related symbols and information, preserving other symbols for internal referencing.
• path/to/source_file: The object file to clean up.
• path/to/target_file: The destination file without debugging information.

Example Output:

Successful execution results in a slimmer file devoid of debug symbols, beneficial for streamlined deployment.

Use case 5: Copy a specific section from the source file to the destination file

Code:

objcopy --only-section section path/to/source_file path/to/target_file

Motivation:

In certain scenarios, only specific sections of an object file are needed for further processing or analysis. Extracting sections can be essential for debugging, testing specific features, or creating libraries.

Explanation:

• --only-section section: Specifies the section to be copied. Sections might include .text for code, .data for initialized data, or .bss for uninitialized data.
• path/to/source_file: The original file with sections.
• path/to/target_file: The resulting file where only the specified section is copied.

Example Output:

The output file will contain only the desired section from the source, useful for specialized applications where only partial data is required.

Conclusion:

The objcopy command proves its flexibility and power through various operations on object files. Whether simplifying file formats, stripping unnecessary data, or selectively copying file sections, objcopy supports efficient and adaptable software development workflows. Understanding and applying these use cases enhance management and optimization of binary files for development, testing, and deployment across different environments.