OS Hello world

os/.gitignore

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+build/

os/boot.S

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+.option norvc
+
+.section .init
+
+.equ UART_BASE, 0x10000000
+
+.global kstart
+kstart:
+    la        a0, _str
+    call      _println
+
+_halt:
+    wfi
+    j         _halt
+
+_println:
+    li        t0, UART_BASE
+_println_loop:
+    lb        t1, 0(a0)
+    beqz      t1, _end_println_loop
+    sb        t1, 0(t0)
+    addi      a0, a0, 1
+    j         _println_loop
+_end_println_loop:
+    li        t1, '\n'
+    sb        t1, 0(t0)
+    ret
+
+.section .rodata
+
+_str: .string "Hello, world!"

os/build.bat

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+@echo off
+
+IF NOT EXIST build mkdir build
+
+clang --target=riscv32 -march=rv32im -nostdlib boot.S -c -o build\boot.o
+
+ld.lld -T linker.ld build\boot.o -o build\kernel.elf

os/linker.ld

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+ENTRY(kstart);
+
+MEMORY {
+  ram (wxa) : ORIGIN = 0x80000000, LENGTH = 128M
+}
+
+PHDRS {
+  text   PT_LOAD;
+  rodata PT_LOAD;
+}
+
+SECTIONS {
+  .text : ALIGN(4K) {
+    *(.init);
+    *(.text);
+  } >ram AT>ram :text
+
+  .rodata : ALIGN(4K) {
+    *(.rodata);
+  } >ram AT>ram :rodata
+}
+
+ # @Todo .bss (clear), .data, etc

os/notes.txt

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+qemu-system-riscv32 -machine virt -cpu rv32 -smp 1 -m 128M -nographic -serial mon:stdio -bios none -kernel kernel.elf
+
+qemu-system-riscv32 -machine virt -cpu rv32 -smp 1 -m 128M -bios none -kernel kernel.elf
+
+cmd /c exit
+
+clang --target=riscv32 -march=rv32im -nostdlib boot.S -c -o boot.o
+
+ld.lld -T linker.ld boot.o -o kernel.elf
+
+static const MemMapEntry virt_memmap[] = {
+    [VIRT_DEBUG] =        {        0x0,         0x100 },
+    [VIRT_MROM] =         {     0x1000,        0xf000 },
+    [VIRT_TEST] =         {   0x100000,        0x1000 },
+    [VIRT_RTC] =          {   0x101000,        0x1000 },
+    [VIRT_CLINT] =        {  0x2000000,       0x10000 },
+    [VIRT_ACLINT_SSWI] =  {  0x2F00000,        0x4000 },
+    [VIRT_PCIE_PIO] =     {  0x3000000,       0x10000 },
+    [VIRT_PLATFORM_BUS] = {  0x4000000,     0x2000000 },
+    [VIRT_PLIC] =         {  0xc000000, VIRT_PLIC_SIZE(VIRT_CPUS_MAX * 2) },
+    [VIRT_APLIC_M] =      {  0xc000000, APLIC_SIZE(VIRT_CPUS_MAX) },
+    [VIRT_APLIC_S] =      {  0xd000000, APLIC_SIZE(VIRT_CPUS_MAX) },
+    [VIRT_UART0] =        { 0x10000000,         0x100 },
+    [VIRT_VIRTIO] =       { 0x10001000,        0x1000 },
+    [VIRT_FW_CFG] =       { 0x10100000,          0x18 },
+    [VIRT_FLASH] =        { 0x20000000,     0x4000000 },
+    [VIRT_IMSIC_M] =      { 0x24000000, VIRT_IMSIC_MAX_SIZE },
+    [VIRT_IMSIC_S] =      { 0x28000000, VIRT_IMSIC_MAX_SIZE },
+    [VIRT_PCIE_ECAM] =    { 0x30000000,    0x10000000 },
+    [VIRT_PCIE_MMIO] =    { 0x40000000,    0x40000000 },
+    [VIRT_DRAM] =         { 0x80000000,           0x0 },
+};

os/run.bat

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+@echo off
+
+qemu-system-riscv32 -machine virt -cpu rv32 -smp 1 -m 128M -nographic -serial mon:stdio -bios none -kernel build\kernel.elf
+
+cmd /c exit