ARMv8: add optional Linux kernel image header

Allow placing a Linux kernel image header at the start of the U-Boot
binary. This is useful since the image header reports the amount of memory
(BSS and similar) that U-Boot needs to use, but that isn't part of the
binary size. This can be used by the code that loads U-Boot into memory to
determine where to load U-Boot, based on other users of memory.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>

5 files changed, 159 insertions, 1 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index c15acdf85c5..001ece3cf14 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -32,6 +32,23 @@ config SYS_INIT_SP_BSS_OFFSET
 	  calculate the stack pointer. This offset should be large enough so
 	  that the early malloc region, global data (gd), and early stack usage
 	  do not overlap any appended DTB.
+
+config LINUX_KERNEL_IMAGE_HEADER
+	bool
+	help
+	  Place a Linux kernel image header at the start of the U-Boot binary.
+	  The format of the header is described in the Linux kernel source at
+	  Documentation/arm64/booting.txt. This feature is useful since the
+	  image header reports the amount of memory (BSS and similar) that
+	  U-Boot needs to use, but which isn't part of the binary.
+
+if LINUX_KERNEL_IMAGE_HEADER
+config LNX_KRNL_IMG_TEXT_OFFSET_BASE
+	hex
+	help
+	  The value subtracted from CONFIG_SYS_TEXT_BASE to calculate the
+	  TEXT_OFFSET value written in to the Linux kernel image header.
+endif
 endif
 
 config STATIC_RELA
diff --git a/arch/arm/cpu/armv8/linux-kernel-image-header-vars.h b/arch/arm/cpu/armv8/linux-kernel-image-header-vars.h
new file mode 100644
index 00000000000..3e720937f01
--- /dev/null
+++ b/arch/arm/cpu/armv8/linux-kernel-image-header-vars.h
@@ -0,0 +1,86 @@
+/*
+ * (C) Copyright 2017 NVIDIA Corporation <www.nvidia.com>
+ *
+ * Derived from Linux kernel v4.14 files:
+ *
+ * arch/arm64/include/asm/assembler.h:
+ * Based on arch/arm/include/asm/assembler.h, arch/arm/mm/proc-macros.S
+ * Copyright (C) 1996-2000 Russell King
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * arch/arm64/kernel/head.S:
+ * Based on arch/arm/kernel/head.S
+ * Copyright (C) 1994-2002 Russell King
+ * Copyright (C) 2003-2012 ARM Ltd.
+ * Authors:	Catalin Marinas <catalin.marinas@arm.com>
+ *		Will Deacon <will.deacon@arm.com>
+ *
+ * arch/arm64/kernel/image.h:
+ * Copyright (C) 2014 ARM Ltd.
+ *
+ * SPDX-License-Identifier:     GPL-2.0
+ */
+
+/*
+ * 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.
+ *
+ * Note that, in order for this to work when building the ELF64 PIE executable
+ * (for KASLR), these values should not be referenced via R_AARCH64_ABS64
+ * relocations, since these are fixed up at runtime rather than at build time
+ * when PIE is in effect. So we need to split them up in 32-bit high and low
+ * words.
+ */
+#ifdef CONFIG_CPU_BIG_ENDIAN
+#define DATA_LE32(data)				\
+	((((data) & 0x000000ff) << 24) |	\
+	 (((data) & 0x0000ff00) << 8)  |	\
+	 (((data) & 0x00ff0000) >> 8)  |	\
+	 (((data) & 0xff000000) >> 24))
+#else
+#define DATA_LE32(data) ((data) & 0xffffffff)
+#endif
+
+#define DEFINE_IMAGE_LE64(sym, data)				\
+	sym##_lo32 = DATA_LE32((data) & 0xffffffff);		\
+	sym##_hi32 = DATA_LE32((data) >> 32)
+
+#define __MAX(a, b)		(((a) > (b)) ? (a) : (b))
+#define __CODE_DATA_SIZE	(__bss_start - _start)
+#define __BSS_SIZE		(__bss_end - __bss_start)
+#ifdef CONFIG_SYS_INIT_SP_BSS_OFFSET
+#define __MAX_EXTRA_RAM_USAGE	__MAX(__BSS_SIZE, CONFIG_SYS_INIT_SP_BSS_OFFSET)
+#else
+#define __MAX_EXTRA_RAM_USAGE	__BSS_SIZE
+#endif
+#define __MEM_USAGE		(__CODE_DATA_SIZE + __MAX_EXTRA_RAM_USAGE)
+
+#ifdef CONFIG_CPU_BIG_ENDIAN
+#define __HEAD_FLAG_BE		1
+#else
+#define __HEAD_FLAG_BE		0
+#endif
+
+#define __HEAD_FLAG_PAGE_SIZE	1 /* 4K hard-coded */
+
+#define __HEAD_FLAG_PHYS_BASE	1
+
+#define __HEAD_FLAGS		((__HEAD_FLAG_BE << 0) |	\
+				 (__HEAD_FLAG_PAGE_SIZE << 1) |	\
+				 (__HEAD_FLAG_PHYS_BASE << 3))
+
+#define TEXT_OFFSET (CONFIG_SYS_TEXT_BASE - \
+			CONFIG_LNX_KRNL_IMG_TEXT_OFFSET_BASE)
+
+/*
+ * 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						\
+	DEFINE_IMAGE_LE64(_kernel_size_le, __MEM_USAGE);	\
+	DEFINE_IMAGE_LE64(_kernel_offset_le, TEXT_OFFSET);	\
+	DEFINE_IMAGE_LE64(_kernel_flags_le, __HEAD_FLAGS);
+
+	HEAD_SYMBOLS
diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
index f385ed40e1a..7a98a1c95d2 100644
--- a/arch/arm/cpu/armv8/start.S
+++ b/arch/arm/cpu/armv8/start.S
@@ -19,7 +19,9 @@
 
 .globl	_start
 _start:
-#ifdef CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK
+#if defined(LINUX_KERNEL_IMAGE_HEADER)
+#include <asm/boot0-linux-kernel-header.h>
+#elif defined(CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK)
 /*
  * Various SoCs need something special and SoC-specific up front in
  * order to boot, allow them to set that in their boot0.h file and then
diff --git a/arch/arm/cpu/armv8/u-boot.lds b/arch/arm/cpu/armv8/u-boot.lds
index 22195b8834b..7b76e0f9f08 100644
--- a/arch/arm/cpu/armv8/u-boot.lds
+++ b/arch/arm/cpu/armv8/u-boot.lds
@@ -159,4 +159,8 @@ SECTIONS
 	/DISCARD/ : { *(.plt*) }
 	/DISCARD/ : { *(.interp*) }
 	/DISCARD/ : { *(.gnu*) }
+
+#ifdef CONFIG_LINUX_KERNEL_IMAGE_HEADER
+#include "linux-kernel-image-header-vars.h"
+#endif
 }
diff --git a/arch/arm/include/asm/boot0-linux-kernel-header.h b/arch/arm/include/asm/boot0-linux-kernel-header.h
new file mode 100644
index 00000000000..ca28780daac
--- /dev/null
+++ b/arch/arm/include/asm/boot0-linux-kernel-header.h
@@ -0,0 +1,49 @@
+/*
+ * (C) Copyright 2017 NVIDIA Corporation <www.nvidia.com>
+ *
+ * Derived from Linux kernel v4.14 files:
+ *
+ * arch/arm64/include/asm/assembler.h:
+ * Based on arch/arm/include/asm/assembler.h, arch/arm/mm/proc-macros.S
+ * Copyright (C) 1996-2000 Russell King
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * arch/arm64/kernel/head.S:
+ * Based on arch/arm/kernel/head.S
+ * Copyright (C) 1994-2002 Russell King
+ * Copyright (C) 2003-2012 ARM Ltd.
+ * Authors:	Catalin Marinas <catalin.marinas@arm.com>
+ *		Will Deacon <will.deacon@arm.com>
+ *
+ * arch/arm64/kernel/image.h:
+ * Copyright (C) 2014 ARM Ltd.
+ *
+ * SPDX-License-Identifier:     GPL-2.0
+ */
+
+	/*
+	 * Emit a 64-bit absolute little endian symbol reference in a way that
+	 * ensures that it will be resolved at build time, even when building a
+	 * PIE binary. This requires cooperation from the linker script, which
+	 * must emit the lo32/hi32 halves individually.
+	 */
+	.macro	le64sym, sym
+	.long	\sym\()_lo32
+	.long	\sym\()_hi32
+	.endm
+
+.globl _start
+_start:
+	/*
+	 * DO NOT MODIFY. Image header expected by Linux boot-loaders.
+	 */
+	b	reset				/* branch to kernel start, magic */
+	.long	0				/* reserved */
+	le64sym	_kernel_offset_le		/* Image load offset from start of RAM, little-endian */
+	le64sym	_kernel_size_le			/* Effective size of kernel image, little-endian */
+	le64sym	_kernel_flags_le		/* Informative flags, little-endian */
+	.quad	0				/* reserved */
+	.quad	0				/* reserved */
+	.quad	0				/* reserved */
+	.ascii	"ARM\x64"			/* Magic number */
+	.long	0				/* reserved */