@@ -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:
new file mode 100644
@@ -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 */
@@ -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
@@ -5,6 +5,7 @@
*/
#include <asm-generic/vmlinux.lds.h>
+#include <asm/image.h>
#include <asm/thread_info.h>
#include <asm/memory.h>
#include <asm/page.h>
@@ -114,6 +115,8 @@ SECTIONS
_end = .;
STABS_DEBUG
+
+ HEAD_SYMBOLS
}
/*