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authorMark Rutland <mark.rutland@arm.com>2014-06-24 16:51:36 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2014-07-10 12:36:40 +0100
commita2c1d73b94ed49f5fac12e95052d7b140783f800 (patch)
treeb76a97b6a9d024eb4975484aa47bccf3c24a9cb8 /arch/arm64
parentbd00cd5f8c8c3c282bb1e1eac6a6679a4f808091 (diff)
downloadlinux-a2c1d73b94ed49f5fac12e95052d7b140783f800.tar.gz
arm64: Update the Image header
Currently the kernel Image is stripped of everything past the initial stack, and at runtime the memory is initialised and used by the kernel. This makes the effective minimum memory footprint of the kernel larger than the size of the loaded binary, though bootloaders have no mechanism to identify how large this minimum memory footprint is. This makes it difficult to choose safe locations to place both the kernel and other binaries required at boot (DTB, initrd, etc), such that the kernel won't clobber said binaries or other reserved memory during initialisation. Additionally when big endian support was added the image load offset was overlooked, and is currently of an arbitrary endianness, which makes it difficult for bootloaders to make use of it. It seems that bootloaders aren't respecting the image load offset at present anyway, and are assuming that offset 0x80000 will always be correct. This patch adds an effective image size to the kernel header which describes the amount of memory from the start of the kernel Image binary which the kernel expects to use before detecting memory and handling any memory reservations. This can be used by bootloaders to choose suitable locations to load the kernel and/or other binaries such that the kernel will not clobber any memory unexpectedly. As before, memory reservations are required to prevent the kernel from clobbering these locations later. Both the image load offset and the effective image size are forced to be little-endian regardless of the native endianness of the kernel to enable bootloaders to load a kernel of arbitrary endianness. Bootloaders which wish to make use of the load offset can inspect the effective image size field for a non-zero value to determine if the offset is of a known endianness. To enable software to determine the endinanness of the kernel as may be required for certain use-cases, a new flags field (also little-endian) is added to the kernel header to export this information. The documentation is updated to clarify these details. To discourage future assumptions regarding the value of text_offset, the value at this point in time is removed from the main flow of the documentation (though kept as a compatibility note). Some minor formatting issues in the documentation are also corrected. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Tom Rini <trini@ti.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Kevin Hilman <kevin.hilman@linaro.org> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64')
-rw-r--r--arch/arm64/kernel/head.S6
-rw-r--r--arch/arm64/kernel/image.h62
-rw-r--r--arch/arm64/kernel/vmlinux.lds.S4
3 files changed, 69 insertions, 3 deletions
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
}
/*