1 ================================================ 2 The Unified Extensible Firmware Interface (UEFI) 3 ================================================ 4 5 UEFI, the Unified Extensible Firmware Interface, is a specification 6 governing the behaviours of compatible firmware interfaces. It is 7 maintained by the UEFI Forum - http://www.uefi.org/. 8 9 UEFI is an evolution of its predecessor 'EFI', so the terms EFI and 10 UEFI are used somewhat interchangeably in this document and associated 11 source code. As a rule, anything new uses 'UEFI', whereas 'EFI' refers 12 to legacy code or specifications. 13 14 UEFI support in Linux 15 ===================== 16 Booting on a platform with firmware compliant with the UEFI specification 17 makes it possible for the kernel to support additional features: 18 19 - UEFI Runtime Services 20 - Retrieving various configuration information through the standardised 21 interface of UEFI configuration tables. (ACPI, SMBIOS, ...) 22 23 For actually enabling [U]EFI support, enable: 24 25 - CONFIG_EFI=y 26 - CONFIG_EFIVAR_FS=y or m 27 28 The implementation depends on receiving information about the UEFI environment 29 in a Flattened Device Tree (FDT) - so is only available with CONFIG_OF. 30 31 UEFI stub 32 ========= 33 The "stub" is a feature that extends the Image/zImage into a valid UEFI 34 PE/COFF executable, including a loader application that makes it possible to 35 load the kernel directly from the UEFI shell, boot menu, or one of the 36 lightweight bootloaders like Gummiboot or rEFInd. 37 38 The kernel image built with stub support remains a valid kernel image for 39 booting in non-UEFI environments. 40 41 UEFI kernel support on ARM 42 ========================== 43 UEFI kernel support on the ARM architectures (arm and arm64) is only available 44 when boot is performed through the stub. 45 46 When booting in UEFI mode, the stub deletes any memory nodes from a provided DT. 47 Instead, the kernel reads the UEFI memory map. 48 49 The stub populates the FDT /chosen node with (and the kernel scans for) the 50 following parameters: 51 52 ========================== ====== =========================================== 53 Name Type Description 54 ========================== ====== =========================================== 55 linux,uefi-system-table 64-bit Physical address of the UEFI System Table. 56 57 linux,uefi-mmap-start 64-bit Physical address of the UEFI memory map, 58 populated by the UEFI GetMemoryMap() call. 59 60 linux,uefi-mmap-size 32-bit Size in bytes of the UEFI memory map 61 pointed to in previous entry. 62 63 linux,uefi-mmap-desc-size 32-bit Size in bytes of each entry in the UEFI 64 memory map. 65 66 linux,uefi-mmap-desc-ver 32-bit Version of the mmap descriptor format. 67 68 kaslr-seed 64-bit Entropy used to randomize the kernel image 69 base address location. 70 71 bootargs String Kernel command line 72 ========================== ====== ===========================================
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