Add comments in ch6

os/src/trap/context.rs

@@ -1,20 +1,30 @@
+//! Implementation of [`TrapContext`]
 use riscv::register::sstatus::{self, Sstatus, SPP};
 
 #[repr(C)]
 #[derive(Debug)]
+///trap context structure containing sstatus, sepc and registers
 pub struct TrapContext {
+    /// general regs[0..31]
     pub x: [usize; 32],
+    /// CSR sstatus      
     pub sstatus: Sstatus,
+    /// CSR sepc
     pub sepc: usize,
+    /// Addr of Page Table
     pub kernel_satp: usize,
+    /// kernel stack
     pub kernel_sp: usize,
+    /// Addr of trap_handler function
     pub trap_handler: usize,
 }
 
 impl TrapContext {
+    ///set stack pointer to x_2 reg (sp)
     pub fn set_sp(&mut self, sp: usize) {
         self.x[2] = sp;
     }
+    ///init app context
     pub fn app_init_context(
         entry: usize,
         sp: usize,