Add trap.rs

src/main.rs

@@ -6,6 +6,7 @@
 use core::panic::PanicInfo;
 
 mod heap;
+mod trap;
 mod uart;
 
 #[naked]
@@ -30,9 +31,17 @@ unsafe extern "C" fn _enter() -> ! {
         "la gp, _global_pointer",
         ".option pop", // pops the current option stack
 
+        // delegate all traps to S-mode trap handler
+        "li t5, 0xffff",
+        "csrw medeleg, t5", // delegate all machine exceptions
+        "csrw mideleg, t5", // delegate all machine interrupts
+
         // set the stack pointer
         "la sp, _init_stack_top",
 
+        "la t2, {trap_vector}",
+        "csrw mtvec, t2",
+
         // clear the BSS
         "la t0, _bss_start",
         "la t1, _bss_end",
@@ -42,13 +51,8 @@ unsafe extern "C" fn _enter() -> ! {
         "addi t0, t0, 1",
         "bne t0, t1, 1b",
     "2:",
-        // BSS is clear!
-
-        // delegate all traps to S-mode trap handler
-        "li t5, 0xffff",
-        "csrw medeleg, t5", // delegate all machine exceptions
-        "csrw mideleg, t5", // delegate all machine interrupts
         "j 4f",
+        // BSS is clear!
     
     // busy loop if hartid =/= 0
     "3:",
@@ -59,6 +63,7 @@ unsafe extern "C" fn _enter() -> ! {
         // "tail-call" to {start} (call without saving a return address)
         "tail {start}",
         start = sym start, // {start} refers to the function [start] below
+        trap_vector = sym trap::trap_handler, // {trap_vector} refers to function [trap::trap_handler]
         options(noreturn) // we must handle "returning" from assembly
     );
 }

src/script.ld

@@ -38,7 +38,7 @@ SECTIONS {
   } >ram AT>ram :bss # and this goes into the bss segment
 
   . = ALIGN(16); # our stack needs to be 16-byte aligned, per the C calling convention
-  PROVIDE(_init_stack_top = . + 0x1000); # reserve 0x1000 bytes for the initialisation stack
+  PROVIDE(_init_stack_top = . + 0x1000); # reserve 0x1000 bytes (4 kB) for the initialisation stack
 
   PROVIDE(_kernel_heap_bottom = _init_stack_top); # allocate heap to remaining physical memory
   PROVIDE(_kernel_heap_top = ORIGIN(ram) + LENGTH(ram)); # top of heap is end of ram

src/trap.rs

@@ -0,0 +1,8 @@
+#[naked]
+pub unsafe extern "C" fn trap_handler() -> ! {
+    use core::arch::asm;
+    asm!(
+        "mret",
+        options(noreturn)
+    );
+}