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077248fcce
Directives such as .long and .word do not magically cause the
assembler location counter to become aligned in gas. As a result,
using these directives in code sections can result in misaligned
data words when building a Thumb-2 kernel (CONFIG_THUMB2_KERNEL).
This is a Bad Thing, since the ABI permits the compiler to assume
that fundamental types of word size or above are word- aligned when
accessing them from C. If the data is not really word-aligned,
this can cause impaired performance and stray alignment faults in
some circumstances.
In general, the following rules should be applied when using data
word declaration directives inside code sections:
* .quad and .double:
.align 3
* .long, .word, .single, .float:
.align (or .align 2)
* .short:
No explicit alignment required, since Thumb-2
instructions are always 2 or 4 bytes in size.
immediately after an instruction.
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
89 lines
2.6 KiB
ArmAsm
89 lines
2.6 KiB
ArmAsm
/*
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* linux/arch/arm/boot/bootp/init.S
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*
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* Copyright (C) 2000-2003 Russell King.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* "Header" file for splitting kernel + initrd. Note that we pass
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* r0 through to r3 straight through.
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*
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* This demonstrates how to append code to the start of the kernel
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* zImage, and boot the kernel without copying it around. This
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* example would be simpler; if we didn't have an object of unknown
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* size immediately following the kernel, we could build this into
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* a binary blob, and concatenate the zImage using the cat command.
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*/
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.section .start,#alloc,#execinstr
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.type _start, #function
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.globl _start
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_start: add lr, pc, #-0x8 @ lr = current load addr
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adr r13, data
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ldmia r13!, {r4-r6} @ r5 = dest, r6 = length
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add r4, r4, lr @ r4 = initrd_start + load addr
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bl move @ move the initrd
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/*
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* Setup the initrd parameters to pass to the kernel. This can only be
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* passed in via the tagged list.
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*/
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ldmia r13, {r5-r9} @ get size and addr of initrd
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@ r5 = ATAG_CORE
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@ r6 = ATAG_INITRD2
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@ r7 = initrd start
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@ r8 = initrd end
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@ r9 = param_struct address
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ldr r10, [r9, #4] @ get first tag
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teq r10, r5 @ is it ATAG_CORE?
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/*
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* If we didn't find a valid tag list, create a dummy ATAG_CORE entry.
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*/
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movne r10, #0 @ terminator
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movne r4, #2 @ Size of this entry (2 words)
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stmneia r9, {r4, r5, r10} @ Size, ATAG_CORE, terminator
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/*
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* find the end of the tag list, and then add an INITRD tag on the end.
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* If there is already an INITRD tag, then we ignore it; the last INITRD
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* tag takes precedence.
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*/
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taglist: ldr r10, [r9, #0] @ tag length
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teq r10, #0 @ last tag (zero length)?
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addne r9, r9, r10, lsl #2
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bne taglist
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mov r5, #4 @ Size of initrd tag (4 words)
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stmia r9, {r5, r6, r7, r8, r10}
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b kernel_start @ call kernel
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/*
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* Move the block of memory length r6 from address r4 to address r5
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*/
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move: ldmia r4!, {r7 - r10} @ move 32-bytes at a time
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stmia r5!, {r7 - r10}
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ldmia r4!, {r7 - r10}
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stmia r5!, {r7 - r10}
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subs r6, r6, #8 * 4
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bcs move
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mov pc, lr
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.size _start, . - _start
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.align
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.type data,#object
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data: .word initrd_start @ source initrd address
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.word initrd_phys @ destination initrd address
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.word initrd_size @ initrd size
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.word 0x54410001 @ r5 = ATAG_CORE
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.word 0x54420005 @ r6 = ATAG_INITRD2
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.word initrd_phys @ r7
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.word initrd_size @ r8
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.word params_phys @ r9
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.size data, . - data
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