UEFI Glossary

AXL abstracts most UEFI details behind its public API, but some concepts surface in documentation and error messages. This glossary defines terms you may encounter.

AP: Application Processor – any CPU core other than the BSP. APs can be dispatched via the MP Services protocol to run compute-heavy tasks (CRC, decompression, hashing) in parallel. APs cannot call Boot Services, use axl_printf, or access UEFI protocols. Use axl_task_pool_submit() to offload work to APs.
Boot Services: Firmware services available before the OS takes control. Accessed via gBS (the Boot Services table pointer). Includes memory allocation, protocol management, event/timer services, and driver loading. AXL wraps most Boot Services behind its API – direct access is needed only for custom protocol calls.
BSP: Bootstrap Processor – the CPU core that executes firmware initialization and runs the main application. All UEFI Boot Services calls must happen on the BSP. AXL functions that interact with firmware (I/O, networking, protocol calls) run on the BSP.
ConOut: Console Output – the UEFI text output protocol (EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL). axl_printf converts UTF-8 to UCS-2 and writes to ConOut. Available on systems with a display or serial console.
Device Path: A UEFI data structure describing the physical or logical path to a device (e.g., PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0)). Used internally by the firmware for boot ordering and device identification.
DXE Driver: Driver Execution Environment driver – a UEFI binary that provides services to other binaries. Built with axl-cc --type driver. Entry point is DriverEntry instead of main. Call axl_driver_init to set up the AXL runtime.
EFI_HANDLE: An opaque pointer identifying a UEFI object (device, driver, application). Handles have protocols installed on them. gImageHandle is the handle of the running application or driver.
EFI_STATUS: The standard UEFI return type – a machine-word integer where 0 = EFI_SUCCESS. AXL functions return int (0 = success, -1 = failure) instead; EFI_STATUS values appear only in direct protocol calls.
GOP: Graphics Output Protocol – the UEFI framebuffer interface. Provides resolution queries, rectangle fill, pixel buffer blit, and screen capture. AXL wraps it via axl_gfx_* functions. Not available on headless or serial-only systems.
OVMF: Open Virtual Machine Firmware – an open-source UEFI firmware implementation for virtual machines (QEMU). Used for testing AXL applications without real hardware.
Protocol: A UEFI interface identified by a GUID. Protocols are installed on handles and discovered via LocateProtocol or LocateHandleBuffer. Examples: TCP4, UDP4, GOP (graphics), SimpleNetwork, Shell. AXL’s axl_service_find wraps protocol lookup with string names instead of GUIDs.
Runtime Services: Firmware services that remain available after the OS boots. Accessed via gRT. Includes NVRAM variable access (GetVariable/SetVariable), system time, and reset. AXL wraps these via axl_nvstore_* and axl_reset.
Service Binding: A protocol pattern for creating child instances. Used by networking protocols (TCP4, UDP4, DNS4) where each connection needs its own protocol instance. CreateChild allocates a new instance; DestroyChild frees it.
SNP: Simple Network Protocol – the lowest-level NIC interface in UEFI. Provides raw Ethernet frame send/receive. Higher-level protocols (IP4, TCP4, UDP4, DHCP4) are built on top of SNP. axl_net_auto_init loads NIC drivers and brings up the SNP → IP4 → TCP4/UDP4 stack.
System Table: The root UEFI data structure (EFI_SYSTEM_TABLE), passed to every UEFI entry point. Contains pointers to Boot Services, Runtime Services, console I/O, and firmware vendor info. Accessed via gST in AXL.