1================================= 2Boot image header in RISC-V Linux 3================================= 4 5:Author: Atish Patra <atish.patra@wdc.com> 6:Date: 20 May 2019 7 8This document only describes the boot image header details for RISC-V Linux. 9 10The following 64-byte header is present in decompressed Linux kernel image:: 11 12 u32 code0; /* Executable code */ 13 u32 code1; /* Executable code */ 14 u64 text_offset; /* Image load offset, little endian */ 15 u64 image_size; /* Effective Image size, little endian */ 16 u64 flags; /* kernel flags, little endian */ 17 u32 version; /* Version of this header */ 18 u32 res1 = 0; /* Reserved */ 19 u64 res2 = 0; /* Reserved */ 20 u64 magic = 0x5643534952; /* Magic number, little endian, "RISCV" */ 21 u32 magic2 = 0x05435352; /* Magic number 2, little endian, "RSC\x05" */ 22 u32 res3; /* Reserved for PE COFF offset */ 23 24This header format is compliant with PE/COFF header and largely inspired from 25ARM64 header. Thus, both ARM64 & RISC-V header can be combined into one common 26header in future. 27 28Notes 29===== 30 31- This header is also reused to support EFI stub for RISC-V. EFI specification 32 needs PE/COFF image header in the beginning of the kernel image in order to 33 load it as an EFI application. In order to support EFI stub, code0 is replaced 34 with "MZ" magic string and res3(at offset 0x3c) points to the rest of the 35 PE/COFF header. 36 37- version field indicate header version number 38 39 ========== ============= 40 Bits 0:15 Minor version 41 Bits 16:31 Major version 42 ========== ============= 43 44 This preserves compatibility across newer and older version of the header. 45 The current version is defined as 0.2. 46 47- The "magic" field is deprecated as of version 0.2. In a future 48 release, it may be removed. This originally should have matched up 49 with the ARM64 header "magic" field, but unfortunately does not. 50 The "magic2" field replaces it, matching up with the ARM64 header. 51 52- In current header, the flags field has only one field. 53 54 ===== ==================================== 55 Bit 0 Kernel endianness. 1 if BE, 0 if LE. 56 ===== ==================================== 57 58- Image size is mandatory for boot loader to load kernel image. Booting will 59 fail otherwise. 60