diff options
| -rw-r--r-- | Documentation/arm64/booting.txt | 43 | ||||
| -rw-r--r-- | arch/arm64/kernel/head.S | 6 | ||||
| -rw-r--r-- | arch/arm64/kernel/image.h | 62 | ||||
| -rw-r--r-- | arch/arm64/kernel/vmlinux.lds.S | 4 |
4 files changed, 104 insertions, 11 deletions
diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt index 37fc4f632176..85af34d55cee 100644 --- a/Documentation/arm64/booting.txt +++ b/Documentation/arm64/booting.txt @@ -72,27 +72,54 @@ The decompressed kernel image contains a 64-byte header as follows: u32 code0; /* Executable code */ u32 code1; /* Executable code */ - u64 text_offset; /* Image load offset */ - u64 res0 = 0; /* reserved */ - u64 res1 = 0; /* reserved */ + u64 text_offset; /* Image load offset, little endian */ + u64 image_size; /* Effective Image size, little endian */ + u64 flags; /* kernel flags, little endian */ u64 res2 = 0; /* reserved */ u64 res3 = 0; /* reserved */ u64 res4 = 0; /* reserved */ u32 magic = 0x644d5241; /* Magic number, little endian, "ARM\x64" */ - u32 res5 = 0; /* reserved */ + u32 res5; /* reserved (used for PE COFF offset) */ Header notes: +- As of v3.17, all fields are little endian unless stated otherwise. + - code0/code1 are responsible for branching to stext. + - when booting through EFI, code0/code1 are initially skipped. res5 is an offset to the PE header and the PE header has the EFI - entry point (efi_stub_entry). When the stub has done its work, it + entry point (efi_stub_entry). When the stub has done its work, it jumps to code0 to resume the normal boot process. -The image must be placed at the specified offset (currently 0x80000) -from the start of the system RAM and called there. The start of the -system RAM must be aligned to 2MB. +- Prior to v3.17, the endianness of text_offset was not specified. In + these cases image_size is zero and text_offset is 0x80000 in the + endianness of the kernel. Where image_size is non-zero image_size is + little-endian and must be respected. Where image_size is zero, + text_offset can be assumed to be 0x80000. + +- The flags field (introduced in v3.17) is a little-endian 64-bit field + composed as follows: + Bit 0: Kernel endianness. 1 if BE, 0 if LE. + Bits 1-63: Reserved. + +- When image_size is zero, a bootloader should attempt to keep as much + memory as possible free for use by the kernel immediately after the + end of the kernel image. The amount of space required will vary + depending on selected features, and is effectively unbound. + +The Image must be placed text_offset bytes from a 2MB aligned base +address near the start of usable system RAM and called there. Memory +below that base address is currently unusable by Linux, and therefore it +is strongly recommended that this location is the start of system RAM. +At least image_size bytes from the start of the image must be free for +use by the kernel. + +Any memory described to the kernel (even that below the 2MB aligned base +address) which is not marked as reserved from the kernel e.g. with a +memreserve region in the device tree) will be considered as available to +the kernel. Before jumping into the kernel, the following conditions must be met: diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 15d3c02a38d0..3ba0fc02c0de 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -108,9 +108,9 @@ efi_head: b stext // branch to kernel start, magic .long 0 // reserved #endif - .quad TEXT_OFFSET // Image load offset from start of RAM - .quad 0 // reserved - .quad 0 // reserved + .quad _kernel_offset_le // Image load offset from start of RAM, little-endian + .quad _kernel_size_le // Effective size of kernel image, little-endian + .quad _kernel_flags_le // Informative flags, little-endian .quad 0 // reserved .quad 0 // reserved .quad 0 // reserved diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h new file mode 100644 index 000000000000..8fae0756e175 --- /dev/null +++ b/arch/arm64/kernel/image.h @@ -0,0 +1,62 @@ +/* + * Linker script macros to generate Image header fields. + * + * Copyright (C) 2014 ARM Ltd. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ +#ifndef __ASM_IMAGE_H +#define __ASM_IMAGE_H + +#ifndef LINKER_SCRIPT +#error This file should only be included in vmlinux.lds.S +#endif + +/* + * There aren't any ELF relocations we can use to endian-swap values known only + * at link time (e.g. the subtraction of two symbol addresses), so we must get + * the linker to endian-swap certain values before emitting them. + */ +#ifdef CONFIG_CPU_BIG_ENDIAN +#define DATA_LE64(data) \ + ((((data) & 0x00000000000000ff) << 56) | \ + (((data) & 0x000000000000ff00) << 40) | \ + (((data) & 0x0000000000ff0000) << 24) | \ + (((data) & 0x00000000ff000000) << 8) | \ + (((data) & 0x000000ff00000000) >> 8) | \ + (((data) & 0x0000ff0000000000) >> 24) | \ + (((data) & 0x00ff000000000000) >> 40) | \ + (((data) & 0xff00000000000000) >> 56)) +#else +#define DATA_LE64(data) ((data) & 0xffffffffffffffff) +#endif + +#ifdef CONFIG_CPU_BIG_ENDIAN +#define __HEAD_FLAG_BE 1 +#else +#define __HEAD_FLAG_BE 0 +#endif + +#define __HEAD_FLAGS (__HEAD_FLAG_BE << 0) + +/* + * These will output as part of the Image header, which should be little-endian + * regardless of the endianness of the kernel. While constant values could be + * endian swapped in head.S, all are done here for consistency. + */ +#define HEAD_SYMBOLS \ + _kernel_size_le = DATA_LE64(_end - _text); \ + _kernel_offset_le = DATA_LE64(TEXT_OFFSET); \ + _kernel_flags_le = DATA_LE64(__HEAD_FLAGS); + +#endif /* __ASM_IMAGE_H */ diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index c6648d301adf..a814768ae148 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -9,6 +9,8 @@ #include <asm/memory.h> #include <asm/page.h> +#include "image.h" + #define ARM_EXIT_KEEP(x) #define ARM_EXIT_DISCARD(x) x @@ -114,6 +116,8 @@ SECTIONS _end = .; STABS_DEBUG + + HEAD_SYMBOLS } /* |