mirror of
https://github.com/ivoszbg/uniLoader.git
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741f3e6a61
The C runtime requires that uninitialized global variables are zero. In a bare-metal environment, memory contents are undefined at startup and the BSS section is not automatically cleared, so we must zero out this entire section ourselves. Without this, static variables contain garbage values, leading to unpredictable behavior. For example, the simplefb driver uses a static variable to track the current print position, which resulted in text being drawn at random locations on the screen.
71 lines
1.3 KiB
ArmAsm
71 lines
1.3 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (c) 2022, Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>
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*/
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#include "asmdefs.h"
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.section .text
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ENTRY(_start)
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/* disable interrupts */
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mrs r0, cpsr
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orr r0, r0, #(0x1 << 7)
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orr r0, r0, #(0x1 << 6)
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msr cpsr_c, r0
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mrc p15, 0, r12, c1, c0, 0
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/* i/d cache disable, mmu disabled */
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bic r12, #(1<<12)
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bic r12, #(1<<2 | 1<<0)
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mcr p15, 0, r12, c1, c0, 0
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ldr sp, =__stack_top
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/* Zero BSS section */
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ldr r0, =__bss_start
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ldr r1, =__bss_end
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mov r2, #0
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1:
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cmp r0, r1
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bge 2f
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str r2, [r0], #4
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b 1b
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2:
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/* main(void* dt, void* kernel, void* ramdisk) */
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ldr r0, =_dt_start @ Load address of dtb into r0
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ldr r1, =_kernel_start @ Load address of kernel into r1
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ldr r2, =_ramdisk_start @ Load address of ramdisk into r2
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b main
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END(_start)
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ENTRY(load_kernel_and_jump)
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mov r1, #0 @ machine type = 0 (device tree)
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mov r0, #0 @ reserved
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bx r3
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END(load_kernel_and_jump)
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/* embedding kernel and dt */
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.section .rodata
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ENTRY(_kernel_start)
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.incbin "blob/Image"
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END(_kernel_start)
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ENTRY_ALIAS(_kernel_end)
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ENTRY_ALIAS(kernel_size)
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.word _kernel_end - _kernel_start
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ENTRY(_dt_start)
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.incbin "blob/dtb"
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END(_dt_start)
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ENTRY(_ramdisk_start)
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.incbin "blob/ramdisk"
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END(_ramdisk_start)
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ENTRY_ALIAS(_ramdisk_end)
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ENTRY_ALIAS(ramdisk_size)
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.word _ramdisk_end - _ramdisk_start
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