Best Languages for UEFI Drivers and Applications

Developing Unified Extensible Firmware Interface (UEFI) drivers and applications requires programming languages capable of low-level hardware control, operating in environments without a traditional operating system, and executing before the kernel loads. While the standard UEFI specification is fundamentally architected around the C programming language, low-level platform constraints and modern safety requirements have shaped the use of several other languages, including Assembly, Rust, and restricted subsets of C++.

C: The Industry Standard

C is the primary and official language used for developing UEFI drivers and applications. The UEFI Specification and the industry-standard implementation framework, TianoCore EDK II (EFI Development Kit II), are written almost entirely in C.

UEFI relies on freestanding C (typically C99 or C11), meaning it runs without standard C library (libc) dependencies. Instead, the UEFI specification provides its own extensive set of system table pointers, protocols, and boot/runtime services that replace conventional OS-level abstractions. Drivers and applications are compiled into standalone PE/COFF (Portable Executable) binaries, which the UEFI firmware dispatcher can locate and execute directly from firmware volumes or external storage devices.

Assembly: Low-Level Bootstrap and CPU Initialization

Assembly language (specifically for architectures like x86, x64, ARM, and RISC-V) is essential for the earliest stages of the UEFI boot process. Although modern UEFI implementations minimize Assembly usage in favor of C, it is strictly required during the Security (SEC) phase and the earliest moments of the Pre-EFI Initialization (PEI) phase.

Assembly handles tasks that cannot be accomplished in pure C, including:

• Setting up the initial CPU state and processor registers.
• Transitioning from real mode to protected mode and long mode on x86 architectures.
• Configuring Cache-as-RAM (CAR) to establish an initial stack before the physical memory controller is initialized.

Once basic stack and execution environments are initialized, control is handed over to C, and Assembly is rarely needed for standard UEFI device drivers or applications.

Rust: The Modern Memory-Safe Alternative

Rust has emerged as a viable and increasingly popular language for writing UEFI applications and drivers. Because firmware runs at the highest privilege levels (Ring 0 / SMM), memory safety vulnerabilities can compromise the entire platform before the operating system boots.

Through bare-metal (no_std) support, Rust can compile to the appropriate PE/COFF format without a runtime environment. Open-source crates such as uefi-rs provide safe wrappers around standard UEFI protocols, boot services, and system tables. This allows developers to write UEFI drivers, bootloaders, and utilities with compile-time memory safety, strict type checking, and zero-cost abstractions, avoiding common C pitfalls such as buffer overflows and dangling pointers.

C++: Specialized and Constrained Use

Standard C++ is generally avoided in UEFI driver development due to its runtime dependencies, name mangling, and complex features like exceptions and dynamic type identification (RTTI), which are unsupported in bare-metal UEFI environments.

However, developers can use a restricted subset of C++ (often referred to as "Embedded C++" or "C with Classes"). If features that depend on an underlying runtime are disabled via compiler flags (such as -fno-exceptions and -fno-rtti), developers can take advantage of C++ features like namespaces, function overloading, templates, and RAII (Resource Acquisition Is Initialization) to build cleaner abstractions for UEFI applications.