diff options
| -rw-r--r-- | Documentation/riscv/boot-image-header.txt | 50 | ||||
| -rw-r--r-- | arch/riscv/include/asm/image.h | 65 | ||||
| -rw-r--r-- | arch/riscv/kernel/head.S | 32 |
3 files changed, 147 insertions, 0 deletions
diff --git a/Documentation/riscv/boot-image-header.txt b/Documentation/riscv/boot-image-header.txt new file mode 100644 index 000000000000..1b73fea23b39 --- /dev/null +++ b/Documentation/riscv/boot-image-header.txt @@ -0,0 +1,50 @@ + Boot image header in RISC-V Linux + ============================================= + +Author: Atish Patra <atish.patra@wdc.com> +Date : 20 May 2019 + +This document only describes the boot image header details for RISC-V Linux. +The complete booting guide will be available at Documentation/riscv/booting.txt. + +The following 64-byte header is present in decompressed Linux kernel image. + + u32 code0; /* Executable code */ + u32 code1; /* Executable code */ + u64 text_offset; /* Image load offset, little endian */ + u64 image_size; /* Effective Image size, little endian */ + u64 flags; /* kernel flags, little endian */ + u32 version; /* Version of this header */ + u32 res1 = 0; /* Reserved */ + u64 res2 = 0; /* Reserved */ + u64 magic = 0x5643534952; /* Magic number, little endian, "RISCV" */ + u32 res3; /* Reserved for additional RISC-V specific header */ + u32 res4; /* Reserved for PE COFF offset */ + +This header format is compliant with PE/COFF header and largely inspired from +ARM64 header. Thus, both ARM64 & RISC-V header can be combined into one common +header in future. + +Notes: +- This header can also be reused to support EFI stub for RISC-V in future. EFI + specification needs PE/COFF image header in the beginning of the kernel image + in order to load it as an EFI application. In order to support EFI stub, + code0 should be replaced with "MZ" magic string and res5(at offset 0x3c) should + point to the rest of the PE/COFF header. + +- version field indicate header version number. + Bits 0:15 - Minor version + Bits 16:31 - Major version + + This preserves compatibility across newer and older version of the header. + The current version is defined as 0.1. + +- res3 is reserved for offset to any other additional fields. This makes the + header extendible in future. One example would be to accommodate ISA + extension for RISC-V in future. For current version, it is set to be zero. + +- In current header, the flag field has only one field. + Bit 0: Kernel endianness. 1 if BE, 0 if LE. + +- Image size is mandatory for boot loader to load kernel image. Booting will + fail otherwise. diff --git a/arch/riscv/include/asm/image.h b/arch/riscv/include/asm/image.h new file mode 100644 index 000000000000..ef28e106f247 --- /dev/null +++ b/arch/riscv/include/asm/image.h @@ -0,0 +1,65 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef __ASM_IMAGE_H +#define __ASM_IMAGE_H + +#define RISCV_IMAGE_MAGIC "RISCV" + +#define RISCV_IMAGE_FLAG_BE_SHIFT 0 +#define RISCV_IMAGE_FLAG_BE_MASK 0x1 + +#define RISCV_IMAGE_FLAG_LE 0 +#define RISCV_IMAGE_FLAG_BE 1 + +#ifdef CONFIG_CPU_BIG_ENDIAN +#error conversion of header fields to LE not yet implemented +#else +#define __HEAD_FLAG_BE RISCV_IMAGE_FLAG_LE +#endif + +#define __HEAD_FLAG(field) (__HEAD_FLAG_##field << \ + RISCV_IMAGE_FLAG_##field##_SHIFT) + +#define __HEAD_FLAGS (__HEAD_FLAG(BE)) + +#define RISCV_HEADER_VERSION_MAJOR 0 +#define RISCV_HEADER_VERSION_MINOR 1 + +#define RISCV_HEADER_VERSION (RISCV_HEADER_VERSION_MAJOR << 16 | \ + RISCV_HEADER_VERSION_MINOR) + +#ifndef __ASSEMBLY__ +/** + * struct riscv_image_header - riscv kernel image header + * @code0: Executable code + * @code1: Executable code + * @text_offset: Image load offset (little endian) + * @image_size: Effective Image size (little endian) + * @flags: kernel flags (little endian) + * @version: version + * @res1: reserved + * @res2: reserved + * @magic: Magic number + * @res3: reserved (will be used for additional RISC-V specific + * header) + * @res4: reserved (will be used for PE COFF offset) + * + * The intention is for this header format to be shared between multiple + * architectures to avoid a proliferation of image header formats. + */ + +struct riscv_image_header { + u32 code0; + u32 code1; + u64 text_offset; + u64 image_size; + u64 flags; + u32 version; + u32 res1; + u64 res2; + u64 magic; + u32 res3; + u32 res4; +}; +#endif /* __ASSEMBLY__ */ +#endif /* __ASM_IMAGE_H */ diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S index e368106f2228..0f1ba17e476f 100644 --- a/arch/riscv/kernel/head.S +++ b/arch/riscv/kernel/head.S @@ -11,9 +11,41 @@ #include <asm/thread_info.h> #include <asm/page.h> #include <asm/csr.h> +#include <asm/image.h> __INIT ENTRY(_start) + /* + * Image header expected by Linux boot-loaders. The image header data + * structure is described in asm/image.h. + * Do not modify it without modifying the structure and all bootloaders + * that expects this header format!! + */ + /* jump to start kernel */ + j _start_kernel + /* reserved */ + .word 0 + .balign 8 +#if __riscv_xlen == 64 + /* Image load offset(2MB) from start of RAM */ + .dword 0x200000 +#else + /* Image load offset(4MB) from start of RAM */ + .dword 0x400000 +#endif + /* Effective size of kernel image */ + .dword _end - _start + .dword __HEAD_FLAGS + .word RISCV_HEADER_VERSION + .word 0 + .dword 0 + .asciz RISCV_IMAGE_MAGIC + .word 0 + .balign 4 + .word 0 + +.global _start_kernel +_start_kernel: /* Mask all interrupts */ csrw CSR_SIE, zero csrw CSR_SIP, zero |