Merge ch6 to ch7: Merge ch4 to ch5: fix: set 4 bytes align for kernel trap entry

Author: Azure-stars

os/src/trap/mod.rs

@@ -36,8 +36,11 @@ pub fn init() {
 }
 
 fn set_kernel_trap_entry() {
+    extern "C" {
+        fn __trap_from_kernel();
+    }
     unsafe {
-        stvec::write(trap_from_kernel as usize, TrapMode::Direct);
+        stvec::write(__trap_from_kernel as usize, TrapMode::Direct);
     }
 }
 

os/src/trap/trap.S

@@ -67,3 +67,20 @@ __restore:
     # back to user stack
     ld sp, 2*8(sp)
     sret
+
+    .section .data
+    # emergency stack for kernel trap
+    # in order to print trap info even if the kernel stack is corrupted.
+__emergency:
+    .align 4
+    .space 1024 * 4
+__emergency_end:
+
+
+    .section .text
+    .globl __trap_from_kernel
+    # 2^2=4 bytes aligned for stvec
+    .align 2
+__trap_from_kernel:
+    la sp, __emergency_end
+    j trap_from_kernel