使得DragonOS kernel 能为riscv64编译通过(尚未能启动) (#457)

* 使得DragonOS kernel 能为riscv64编译通过(尚未能启动)

* 修正了系统调用号声明不正确的问题，同时添加了编译配置文档

kernel/src/syscall/misc.rs

@@ -1,4 +1,10 @@
-use crate::arch::mm::LockedFrameAllocator;
+use alloc::vec::Vec;
+
+use crate::{
+    arch::{mm::LockedFrameAllocator, rand::rand},
+    libs::rand::GRandFlags,
+    mm::allocator::page_frame::FrameAllocator,
+};
 
 use super::{user_access::UserBufferWriter, Syscall, SystemError};
 
@@ -30,7 +36,7 @@ impl Syscall {
         let mut writer = UserBufferWriter::new(info, core::mem::size_of::<SysInfo>(), true)?;
         let mut sysinfo = SysInfo::default();
 
-        let mem = LockedFrameAllocator.get_usage();
+        let mem = unsafe { LockedFrameAllocator.usage() };
         sysinfo.uptime = 0;
         sysinfo.loads = [0; 3];
         sysinfo.totalram = mem.total().bytes() as u64;
@@ -54,4 +60,28 @@ impl Syscall {
         kwarn!("SYS_UMASK has not yet been implemented\n");
         return Ok(0o777);
     }
+
+    /// ## 将随机字节填入buf
+    ///
+    /// ### 该系统调用与linux不一致，因为目前没有其他随机源
+    pub fn get_random(buf: *mut u8, len: usize, flags: GRandFlags) -> Result<usize, SystemError> {
+        if flags.bits() == (GRandFlags::GRND_INSECURE.bits() | GRandFlags::GRND_RANDOM.bits()) {
+            return Err(SystemError::EINVAL);
+        }
+
+        let mut writer = UserBufferWriter::new(buf, len, true)?;
+
+        let mut ret = Vec::new();
+        let mut count = 0;
+        while count < len {
+            let rand = rand();
+            for offset in 0..4 {
+                ret.push((rand >> offset * 2) as u8);
+                count += 1;
+            }
+        }
+
+        writer.copy_to_user(&ret, 0)?;
+        Ok(len)
+    }
 }