Initial Commit

Makefile

@@ -0,0 +1,18 @@
+CC	:= $(PREFIX)gcc
+AS	:= $(PREFIX)as
+OBJCPY	:= $(PREFIX)objcopy
+
+boot.o: boot.S
+	$(AS) -c boot.S -o boot.o
+
+kernel.o: kernel.c
+	$(CC) -ffreestanding -c kernel.c -o kernel.o -O2 -Wall -Wextra
+	
+os.elf: boot.o kernel.o linker.ld
+	$(CC) -T linker.ld -o os.elf -ffreestanding -O2 -nostdlib boot.o kernel.o -lgcc
+	
+kernel8.img: os.elf
+	$(OBJCPY) os.elf -O binary kernel8.img
+
+clean:
+	rm boot.o kernel.o os.elf kernel8.img

boot.S

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+// AArch64 mode
+
+// To keep this in the first portion of the binary.
+.section ".text.boot"
+
+// Make _start global.
+.globl _start
+
+    .org 0x80000
+// Entry point for the kernel. Registers:
+// x0 -> 32 bit pointer to DTB in memory (primary core only) / 0 (secondary cores)
+// x1 -> 0
+// x2 -> 0
+// x3 -> 0
+// x4 -> 32 bit kernel entry point, _start location
+_start:
+    // set stack before our code
+    ldr     x5, =_start
+    mov     sp, x5
+
+    // clear bss
+    ldr     x5, =__bss_start
+    ldr     w6, =__bss_size
+1:  cbz     w6, 2f
+    str     xzr, [x5], #8
+    sub     w6, w6, #1
+    cbnz    w6, 1b
+
+    // jump to C code, should not return
+2:  bl      kernel_main
+    // for failsafe, halt this core
+halt:
+    wfe
+    b halt

kernel.c

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+#include <stddef.h>
+#include <stdint.h>
+
+volatile uint32_t** core_1 = (void*)0xE0;
+volatile uint32_t** core_2 = (void*)0xE0;
+volatile uint32_t** core_3 = (void*)0xE0;
+
+
+void _start_core_1(void* addr) {
+    *core_1 = (uint32_t*)addr;
+}
+
+
+void _start_core_2(void* addr) {
+    *core_2 = (uint32_t*)addr;
+}
+
+
+void _start_core_3(void* addr) {
+    *core_3 = (uint32_t*)addr;
+}
+
+
+void kernel_main(uint64_t dtb_ptr32, uint64_t x1, uint64_t x2, uint64_t x3) {
+    return;
+}

linker.ld

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+ENTRY(_start)
+
+SECTIONS
+{
+    /* Starts at LOADER_ADDR. */
+    . = 0x80000;
+    /* For AArch64, use . = 0x80000; */
+    __start = .;
+    __text_start = .;
+    .text :
+    {
+        KEEP(*(.text.boot))
+        *(.text)
+    }
+    . = ALIGN(4096); /* align to page size */
+    __text_end = .;
+
+    __rodata_start = .;
+    .rodata :
+    {
+        *(.rodata)
+    }
+    . = ALIGN(4096); /* align to page size */
+    __rodata_end = .;
+
+    __data_start = .;
+    .data :
+    {
+        *(.data)
+    }
+    . = ALIGN(4096); /* align to page size */
+    __data_end = .;
+
+    __bss_start = .;
+    .bss :
+    {
+        bss = .;
+        *(.bss)
+    }
+    . = ALIGN(4096); /* align to page size */
+    __bss_end = .;
+    __bss_size = __bss_end - __bss_start;
+    __end = .;
+}