Project ESSTRA, a software suite for Enhancing Software Supply Chain Transparency, aims to improve transparency of software supply chains as the name suggests.

More specifically, the goal of the project is to provide a set of tools to help illuminate and unveil the "dark" areas in the software supply chain where critical information about software components is unclear, primarily from a software traceability and compliance perspective.

In the current version of ESSTRA, metadata is embedded into the resulting binary files at compile time using GCC. The metadata contains information about the source and header files from which the binary file has been generated.

For detailed usage and applications, please refer to the Samples that help you understand ESSTRA using simple source code, as well as the Case Study documentation on using ESSTRA for open-source software and Linux distributions.

For a detailed overview of ESSTRA, please refer to the presentation delivered at Open Source Summit Europe 2025.

ESSTRA is developed and tested on a PC (x86_64 architecture) running Ubuntu 24.04, using GCC 13.3.0 and Python 3.12.3. Compatibility testing has also been conducted on Ubuntu 22.04 with GCC 11.4.0 and Python 3.10.12.

We have also confirmed that ESSTRA can be built and run on an Aarch64 (arm64) Docker container virtualized with QEMU on an x86_64 PC.

The current version of ESSTRA consists of the three tools:

• ESSTRA Core
• ESSTRA Link
• ESSTRA Utility

ESSTRA Core (esstracore.so) is a GCC plugin that intervenes the compilation process to embed metadata into the resulting binary files (i.e., object files). In the current version, metadata is embedded for all source and header files involved in the compilation, including their absolute paths and checksums.

ESSTRA Link (esstralink.so) is a GNU linker plugin that performs post-processing during the linking phase of GCC to optimize the metadata embedded in the resulting binary file. Specifically, it removes redundant entries from the metadata originating from multiple object files, ensuring the uniqueness of the information.

ESSTRA Utility (esstra) is a Python script that provides access to the metadata embedded in binary files by ESSTRA Core and ESSTRA Link. It offers functionality such as displaying metadata contents, attaching related information, and removing metadata from binary files. In this version, you can output metadata in YAML format, shrink metadata by removing duplication, and attach license information to metadata by specifying files in the SPDX 2.3 tag-value format which contain license information.

ESSTRA Core creates an ELF section in the resulting object file to store metadata during compilation.

ESSTRA Link performs post-linking analysis to inspect and optimize the metadata merged by the linker.

ESSTRA Utility allows users to access the metadata. For example, you can update the metadata using license information detected from the source files, delete some or all of the metadata, output the metadata to the console, or pass it to other SCA (Software Composition Analysis) tools.

Before you build the GCC plugin, you have to install a package on your system. For Debian/Ubuntu, check the version of GCC first:

$ gcc --version
gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
...
or
$ gcc -dumpversion
13

In this case, the major version is 13, so install the package named gcc-13-plugin-dev:

$ sudo apt install gcc-13-plugin-dev

Since ESSTRA Utility uses the PyYAML module to handle YAML data, you may need to install it:

$ sudo apt install python3-yaml

After that, run make in the top directory:

$ make

If no errors, the build is complete.

To install ESSTRA Core, ESSTRA Link and ESSTRA Utility on your system, run the following command:

$ sudo make install

Then, esstracore.so and esstralink.so are installed to /usr/local/lib/gcc/<gcc-arch>/<gcc-major-version>/plugin/, and the script esstra is installed to /usr/local/bin/ by default. Please make sure that /usr/local/bin is included in your system's PATH.

Here, <gcc-arch> refers to a string like x86_64-linux-gnu, which can be obtained using the gcc -dumpmachine command, and <gcc-major-version> refers to a number like 13, obtained via gcc -dumpversion.

In the case of our development environment mentioned above, the installation path of esstracore.so and esstralink.so is /usr/local/lib/gcc/x86_64-linux-gnu/13/plugin/.

The workflow using ESSTRA consists of the following steps:

1. Compile source files with GCC using ESSTRA Core to generate object files.
2. Link the object files using ESSTRA Link to produce the binary file.
3. Access the metadata embedded in the binary file using ESSTRA Utility.

The example below compiles the source file main.c and sub.c with gcc and generates the binary file hello.

First, compile the source file main.c and sub.c by passing the path of esstracore.so to the compiler with the option -fplugin=:

$ gcc -fplugin=/usr/local/.../esstracore.so -c main.c -o main.o
$ gcc -fplugin=/usr/local/.../esstracore.so -c sub.c -o sub.o

Then the intervention of esstracore.so embeds metadata in the resulting object files main.o and sub.o.

For more details on ESSTRA Core, please refer to core/README.md.

Since gcc allows linker options to be specified using the -Wl,<option> flag, the following command links the object files and produces the binary file hello, while passing the path to esstralink.so to the linker via the -plugin= option:

$ gcc -Wl,-plugin=/usr/local/.../esstralink.so main.o sub.o -o hello

As a result, the generated hello binary file contains optimized metadata inherited from the object files main.o and sub.o.

Note that ESSTRA's intervention in the compilation and linking process does not affect the behavior of the resulting binary files.

For more details on ESSTRA Link, please refer to link/README.md.

The entire process can also be performed in a single command:

$ gcc -fplugin=/usr/local/.../esstracore.so \
      -Wl,-plugin=/usr/local/.../esstralink.so \
      main.c sub.c -o hello

To access the embedded metadata, use the script esstra. The first argument of this script is a command, and the second or subsequent arguments are the arguments of the command.

The command show outputs metadata in binary files in YAML format to the standard output. A command line:

$ esstra show hello

would generate an output as follows:

#
# BinaryFileName: hello
# BinaryPath: /home/snagao/esstra/samples/hello/hello
#
Headers:
  ToolName: ESSTRA Core
  ToolVersion: 0.4.0
  DataFormatVersion: 0.1.0
  InputFileNames:
  - hello.c
SourceFiles:
- Directory: /home/snagao/esstra/samples/hello
  Files:
  - File: hello.c
    SHA1: 4bbee85215cbcb6a4f1625e4851cca19b0d3f6e2
- Directory: /usr/include
  Files:
  - File: features-time64.h
    SHA1: 57c3c8093c3af70e5851f6d498600e2f6e24fdeb
  - File: features.h
    SHA1: d8725bb98129d6d70ddcbf010021c2841db783f7
  - File: stdc-predef.h
    SHA1: 2fef05d80514ca0be77efec90bda051cf87d771f
  - File: stdio.h
    SHA1: c7181b48c4194cd122024971527aab4056baf600
- Directory: /usr/include/x86_64-linux-gnu/bits
  Files:
  - File: floatn-common.h
    SHA1: 3f37104123a2e6180621331c1da87125808e47bd
  - File: floatn.h
    SHA1: 806b759ab6894a09a3b3a422eec5f2414ba7dab7
  - File: libc-header-start.h
    SHA1: e0a400c194cd3962a342a6504a441920163b799c
  - File: long-double.h
    SHA1: 4e3f5928e816ad29079d1c7d75f3a510a0939ffb
  - File: stdio.h
    SHA1: 521d7cd0f6572f70122386784120cc55d84899bc
  - File: stdio2.h
    SHA1: 6c3ee923db9679a79941a688de72e114a794fc54
  - File: stdio_lim.h
    SHA1: 6210c8ae410ee0f39a6096b0adb9fa86febd3517
  - File: time64.h
    SHA1: ab2017da21608498b58eea37b2aa6a3387ee978c
  - File: timesize.h
    SHA1: f1dd8d62a4d75288654626933edfc82ccf2394a7
  - File: types.h
    SHA1: e5893a9c4c523615c73a51feb9680279608027c6
  - File: typesizes.h
    SHA1: ee94b5a60d007c23bdda9e5c46c8ba40f4eb402c
  - File: wordsize.h
    SHA1: 281ddd3c93f1e8653e809a45b606574c9b691092
- Directory: /usr/include/x86_64-linux-gnu/bits/types
  Files:
  - File: FILE.h
    SHA1: 497924e329d53517631713ae52acb73e870d7d65
  - File: __FILE.h
    SHA1: 274242343e85d1c06e7f5ccc5abf15e120f6e957
  - File: __fpos64_t.h
    SHA1: ac38e294b004f6e2bf18f1c55e03dc80f48d6830
  - File: __fpos_t.h
    SHA1: 760ef77769ac1921f4b1f908cbf06863e2506775
  - File: __mbstate_t.h
    SHA1: e3a4f2ee55e635520db0b4610d2b361e9ce41de7
  - File: struct_FILE.h
    SHA1: 1dbf8bac589cb09e09aa4c1d36913e549a57bcf0
- Directory: /usr/include/x86_64-linux-gnu/gnu
  Files:
  - File: stubs-64.h
    SHA1: f7603fa3908b56e9d1b33c91590db3252e13a799
  - File: stubs.h
    SHA1: be168037b7503a82b1cf694cdbac8c063bb6e476
- Directory: /usr/include/x86_64-linux-gnu/sys
  Files:
  - File: cdefs.h
    SHA1: a419a6372029d89ba38ada0811d34f51df8d09b7
- Directory: /usr/lib/gcc/x86_64-linux-gnu/11/include
  Files:
  - File: stdarg.h
    SHA1: fa23f49da8a0a5068b781dff7182f1a1c363dc30
  - File: stddef.h
    SHA1: 0de70008ffa3f198baf55c7b3f3d03b4ca11c21f

For more details on ESSTRA Utility and the structure of the metadata, please refer to util/README.md.

Specifying -fplugin=... and -Wl,-plugin=... every time you run gcc or g++ can be tedious. To simplify this process, run the following command:

$ sudo make install-specs

This installs a GCC spec file that configures your system to automatically apply the following options:

• -fplugin=/usr/local/.../esstracore.so (for gcc/g++)
• -plugin=/usr/local/.../esstralink.so (for ld)

After installation, you can compile your code as usual:

$ gcc main.c sub.c -o hello

ESSTRA Core and ESSTRA Link will be automatically used during compilation and linking, embedding and optimizing metadata in the resulting binary hello.

This is a very handy feature when you want to get the information ESSTRA generates while compiling any kind of project -- whether it's open-source or closed-source.

To uninstall the spec file, run:

$ sudo make uninstall-specs

To uninstall the ESSTRA Core, the ESSTRA Utility, and spec file from your system, run the following command in the top directory :

$ sudo make uninstall

See the LICENSE file.