Try batch but kernel panicked.

os/src/trap/context.rs

@@ -0,0 +1,23 @@
+use riscv::register::sstatus::{Sstatus, self, SPP};
+
+#[repr(C)]
+pub struct TrapContext {
+    x: [usize; 32],
+    sstatus: Sstatus,
+    sepc: usize,
+}
+
+impl TrapContext {
+    pub fn set_sp(&mut self, sp: usize) { self.x[2] = sp; }
+    pub fn app_init_context(entry: usize, sp: usize) -> Self {
+        let mut sstatus = sstatus::read();
+        sstatus.set_spp(SPP::User);
+        let mut cx = Self {
+            x: [0; 32],
+            sstatus,
+            sepc: entry,
+        };
+        cx.set_sp(sp);
+        cx
+    }
+}

os/src/trap/mod.rs

@@ -0,0 +1,38 @@
+mod context;
+
+use riscv::register::{
+    mtvec::TrapMode,
+    stvec,
+    scause::{
+        self,
+        Trap,
+        Exception,
+    },
+    stval,
+};
+
+global_asm!(include_str!("trap.S"));
+
+pub fn init() {
+    extern "C" { fn __alltraps(); }
+    unsafe {
+        stvec::write(__alltraps as usize, TrapMode::Direct);
+    }
+}
+
+#[no_mangle]
+pub fn trap_handler(cx: &mut TrapContext) -> &mut TrapContext {
+    let scause = scause::read();
+    let stval = stval::read();
+    match scause.cause() {
+        Trap::Exception(Exception::UserEnvCall) => {
+            panic!("Triggered UserEnvCall!");
+        }
+        _ => {
+            panic!("Unsupported trap!");
+        }
+    }
+    cx
+}
+
+pub use context::TrapContext;

os/src/trap/trap.S

@@ -0,0 +1,64 @@
+.altmacro
+.macro SAVE_GP n
+    sd x\n, \n*8(sp)
+.endm
+.macro LOAD_GP n
+    ld x\n, \n*8(sp)
+.endm
+    .section .text
+    .globl __alltraps
+    .globl __restore
+    .align 2
+__alltraps:
+    csrrw sp, sscratch, sp
+    # now sp->kernel stack, sscratch->user stack
+    # allocate a TrapContext on kernel stack
+    addi sp, sp, -34*8
+    # save general-purpose registers
+    sd x1, 1*8(sp)
+    # skip sp(x2), we will save it later
+    sd x3, 3*8(sp)
+    # skip tp(x4), application does not use it
+    # save x5~x31
+    .set n, 5
+    .rept 27
+        SAVE_GP %n
+        .set n, n+1
+    .endr
+    # we can use t0/t1/t2 freely, because they were saved on kernel stack
+    csrr t0, sstatus
+    csrr t1, sepc
+    sd t0, 32*8(sp)
+    sd t1, 33*8(sp)
+    # read user stack from sscratch and save it on the kernel stack
+    csrr t2, sscratch
+    sd t2, 2*8(sp)
+    # set input argument of trap_handler(cx: &mut TrapContext)
+    mv a0, sp
+    call trap_handler
+
+__restore:
+    # case1: start running app by __restore
+    # case2: back to U after handling trap
+    mv sp, a0
+    # now sp->kernel stack(after allocated), sscratch->user stack
+    # restore sstatus/sepc
+    ld t0, 32*8(sp)
+    ld t1, 33*8(sp)
+    ld t2, 2*8(sp)
+    csrw sstatus, t0
+    csrw sepc, t1
+    csrw sscratch, t2
+    # restore general-purpuse registers except sp/tp
+    ld x1, 1*8(sp)
+    ld x3, 3*8(sp)
+    .set n, 5
+    .rept 27
+        LOAD_GP %n
+        .set n, n+1
+    .endr
+    # release TrapContext on kernel stack
+    addi sp, sp, 34*8
+    # now sp->kernel stack, sscratch->user stack
+    csrrw sp, sscratch, sp
+    sret