实验二：Qemu 模拟器启动 ArceOS,打印Hello,world

1. 在ArceOS目录下，输入：

   make A=apps/helloworld ARCH=aarch64 PLATFORM=aarch64-raspi4 SMP=4 
   

   （如果4核运行不了，可以改为单核）

   编译出ArceOS在raspi4 上的一个镜像。

2. 在qemu模拟器上运行该镜像：

   ./qemu-system-aarch64 -m 2G -smp 4 -cpu cortex-a72 -machine raspi4b2g -nographic -kernel {yourpath}/helloworld_aarch64-raspi4.bin
   

3. 最后，看到ArceOS在qemu模拟器中成功运行：

   root@DESKTOP-KO8A4KB:~/qemu-patch-raspberry4/build/arceos# make A=apps/helloworld ARCH=aarch64 PLATFORM=aarch64-raspi4 SMP=4
       Building App: helloworld, Arch: aarch64, Platform: aarch64-raspi4, App type: rust
   cargo build --target aarch64-unknown-none-softfloat --target-dir /root/qemu-patch-raspberry4/build/arceos/target --release  --manifest-path 
   apps/helloworld/Cargo.toml --features "axstd/log-level-warn axstd/smp"
       Finished release [optimized] target(s) in 0.09s
   rust-objcopy --binary-architecture=aarch64 apps/helloworld/helloworld_aarch64-raspi4.elf --strip-all -O binary apps/helloworld/helloworld_aarch64-raspi4.bin
   root@DESKTOP-KO8A4KB:~/qemu-patch-raspberry4/build/arceos# cd ..
   root@DESKTOP-KO8A4KB:~/qemu-patch-raspberry4/build# ./qemu-system-aarch64 -m 2G -smp 4 -cpu cortex-a72 -machine raspi4b2g -nographic -kernel 
   arceos/apps/helloworld/helloworld_aarch64-raspi4.bin
   
          d8888                            .d88888b.   .d8888b.
         d88888                           d88P" "Y88b d88P  Y88b
        d88P888                           888     888 Y88b.
       d88P 888 888d888  .d8888b  .d88b.  888     888  "Y888b.
      d88P  888 888P"   d88P"    d8P  Y8b 888     888     "Y88b.
     d88P   888 888     888      88888888 888     888       "888
    d8888888888 888     Y88b.    Y8b.     Y88b. .d88P Y88b  d88P
   d88P     888 888      "Y8888P  "Y8888   "Y88888P"   "Y8888P"
   
   arch = aarch64
   platform = aarch64-raspi4
   target = aarch64-unknown-none-softfloat
   smp = 4
   build_mode = release
   log_level = warn
   
   Hello, world!
   

至此，实验二结束，最终提交实验过程记录（包含出现的各类问题及解决办法）以及ArceOS成功运行，打印Hello，world的结果。