Building and Running C programs on Theseus

Warning: Support for building C programs atop Theseus is experimental and liable to change at any moment.

As Theseus is a safe-language OS that runs all code in a single address space (SAS) and single privilege level (SPL), there is no guarantee of safety, protection, or isolation when running any other unsafe or non-Rust code directly atop Theseus.

Nevertheless, we have introduced experimental support for building C programs atop Theseus; proceed at your own risk.


You must have a version of GCC and Binutils cross-compiled for Theseus, e.g., the x86_64-elf target with red-zone usage disabled.

To make things easy, we have written an automated script and a guide on how to build and install all necessary tools.

Note that the x86_64-elf-* binaries must be on your system PATH before running any of the following gcc commands.

Quickstart: Building a C program

See the c_test directory for an example dummy C program. All it does is run a simple main() function that returns a constant value.

In short, building a C program requires the following steps:

make         # 1. Build Theseus OS itself
make tlibc   # 2. Build tlibc, Theseus's libc
make c_test  # 3. Build a sample C program
make orun    # 4. Run Theseus in QEMU (without rebuilding anything)

Running a C program

Once the C program's executable ELF file has been packaged into Theseus's ISO image, you can execute it in Theseus using the loadc application. Executables are automatically placed in the _executable namespace folder by default, so run the following in Theseus's shell:

loadc /namespaces/_executable/dummy_works

You should observe the return value displayed on the shell GUI, as well as various log messages that show output from tlibc alongside those from Theseus's kernel.

How does it all work?

The following sections describe how to set up the toolchain, how tlibc is built, and how C programs are compiled and linked.