/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* linux/boot/head.S
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*
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* Copyright (C) 1991, 1992, 1993 Linus Torvalds
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*/
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/*
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* head.S contains the 32-bit startup code.
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*
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* NOTE!!! Startup happens at absolute address 0x00001000, which is also where
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* the page directory will exist. The startup code will be overwritten by
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* the page directory. [According to comments etc elsewhere on a compressed
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* kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
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*
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* Page 0 is deliberately kept safe, since System Management Mode code in
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* laptops may need to access the BIOS data stored there. This is also
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* useful for future device drivers that either access the BIOS via VM86
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* mode.
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*/
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/*
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* High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
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*/
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.text
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#include <linux/init.h>
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#include <linux/linkage.h>
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#include <asm/segment.h>
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#include <asm/page_types.h>
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#include <asm/boot.h>
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#include <asm/asm-offsets.h>
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#include <asm/bootparam.h>
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/*
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* These symbols needed to be marked as .hidden to prevent the BFD linker from
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* generating R_386_32 (rather than R_386_RELATIVE) relocations for them when
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* the 32-bit compressed kernel is linked as PIE. This is no longer necessary,
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* but it doesn't hurt to keep them .hidden.
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*/
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.hidden _bss
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.hidden _ebss
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.hidden _end
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__HEAD
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SYM_FUNC_START(startup_32)
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cld
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cli
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/*
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* Calculate the delta between where we were compiled to run
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* at and where we were actually loaded at. This can only be done
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* with a short local call on x86. Nothing else will tell us what
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* address we are running at. The reserved chunk of the real-mode
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* data at 0x1e4 (defined as a scratch field) are used as the stack
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* for this calculation. Only 4 bytes are needed.
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*/
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leal (BP_scratch+4)(%esi), %esp
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call 1f
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1: popl %edx
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addl $_GLOBAL_OFFSET_TABLE_+(.-1b), %edx
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/* Load new GDT */
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leal gdt@GOTOFF(%edx), %eax
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movl %eax, 2(%eax)
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lgdt (%eax)
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/* Load segment registers with our descriptors */
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movl $__BOOT_DS, %eax
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movl %eax, %ds
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movl %eax, %es
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movl %eax, %fs
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movl %eax, %gs
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movl %eax, %ss
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/*
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* %edx contains the address we are loaded at by the boot loader (plus the
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* offset to the GOT). The below code calculates %ebx to be the address where
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* we should move the kernel image temporarily for safe in-place decompression
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* (again, plus the offset to the GOT).
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*
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* %ebp is calculated to be the address that the kernel will be decompressed to.
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*/
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#ifdef CONFIG_RELOCATABLE
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leal startup_32@GOTOFF(%edx), %ebx
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#ifdef CONFIG_EFI_STUB
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/*
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* If we were loaded via the EFI LoadImage service, startup_32() will be at an
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* offset to the start of the space allocated for the image. efi_pe_entry() will
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* set up image_offset to tell us where the image actually starts, so that we
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* can use the full available buffer.
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* image_offset = startup_32 - image_base
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* Otherwise image_offset will be zero and has no effect on the calculations.
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*/
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subl image_offset@GOTOFF(%edx), %ebx
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#endif
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movl BP_kernel_alignment(%esi), %eax
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decl %eax
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addl %eax, %ebx
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notl %eax
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andl %eax, %ebx
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cmpl $LOAD_PHYSICAL_ADDR, %ebx
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jae 1f
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#endif
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movl $LOAD_PHYSICAL_ADDR, %ebx
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1:
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movl %ebx, %ebp // Save the output address for later
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/* Target address to relocate to for decompression */
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addl BP_init_size(%esi), %ebx
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subl $_end@GOTOFF, %ebx
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/* Set up the stack */
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leal boot_stack_end@GOTOFF(%ebx), %esp
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/* Zero EFLAGS */
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pushl $0
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popfl
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/*
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* Copy the compressed kernel to the end of our buffer
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* where decompression in place becomes safe.
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*/
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pushl %esi
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leal (_bss@GOTOFF-4)(%edx), %esi
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leal (_bss@GOTOFF-4)(%ebx), %edi
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movl $(_bss - startup_32), %ecx
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shrl $2, %ecx
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std
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rep movsl
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cld
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popl %esi
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/*
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* The GDT may get overwritten either during the copy we just did or
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* during extract_kernel below. To avoid any issues, repoint the GDTR
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* to the new copy of the GDT.
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*/
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leal gdt@GOTOFF(%ebx), %eax
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movl %eax, 2(%eax)
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lgdt (%eax)
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/*
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* Jump to the relocated address.
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*/
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leal .Lrelocated@GOTOFF(%ebx), %eax
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jmp *%eax
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SYM_FUNC_END(startup_32)
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#ifdef CONFIG_EFI_STUB
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SYM_FUNC_START(efi32_stub_entry)
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SYM_FUNC_START_ALIAS(efi_stub_entry)
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add $0x4, %esp
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movl 8(%esp), %esi /* save boot_params pointer */
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call efi_main
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/* efi_main returns the possibly relocated address of startup_32 */
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jmp *%eax
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SYM_FUNC_END(efi32_stub_entry)
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SYM_FUNC_END_ALIAS(efi_stub_entry)
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#endif
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.text
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SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
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/*
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* Clear BSS (stack is currently empty)
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*/
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xorl %eax, %eax
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leal _bss@GOTOFF(%ebx), %edi
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leal _ebss@GOTOFF(%ebx), %ecx
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subl %edi, %ecx
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shrl $2, %ecx
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rep stosl
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/*
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* Do the extraction, and jump to the new kernel..
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*/
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/* push arguments for extract_kernel: */
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pushl output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */
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pushl %ebp /* output address */
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pushl input_len@GOTOFF(%ebx) /* input_len */
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leal input_data@GOTOFF(%ebx), %eax
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pushl %eax /* input_data */
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leal boot_heap@GOTOFF(%ebx), %eax
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pushl %eax /* heap area */
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pushl %esi /* real mode pointer */
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call extract_kernel /* returns kernel location in %eax */
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addl $24, %esp
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/*
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* Jump to the extracted kernel.
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*/
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xorl %ebx, %ebx
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jmp *%eax
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SYM_FUNC_END(.Lrelocated)
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.data
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.balign 8
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SYM_DATA_START_LOCAL(gdt)
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.word gdt_end - gdt - 1
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.long 0
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.word 0
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.quad 0x0000000000000000 /* Reserved */
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.quad 0x00cf9a000000ffff /* __KERNEL_CS */
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.quad 0x00cf92000000ffff /* __KERNEL_DS */
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SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
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#ifdef CONFIG_EFI_STUB
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SYM_DATA(image_offset, .long 0)
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#endif
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/*
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* Stack and heap for uncompression
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*/
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.bss
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.balign 4
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boot_heap:
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.fill BOOT_HEAP_SIZE, 1, 0
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boot_stack:
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.fill BOOT_STACK_SIZE, 1, 0
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boot_stack_end:
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