Add user_stack_size to Machine and use it for threads sp

src/simulator/mod.rs

@@ -214,7 +214,7 @@ pub mod global {
     /// 
     /// Shift left logical immediate
     /// 
-    /// `SLLI rd, rs1, shamt` => `rd <- rs1 >> shamt`
+    /// `SLLI rd, rs1, shamt` => `rd <- rs1 << shamt`
     pub const RISCV_OPI_SLLI: u8 = 0x1;
     /// Shift right immediate, may be SRAI or SRLI
     pub const RISCV_OPI_SRI: u8 = 0x5;