shrink kstack size, avoid alloc kstack for init thread

kernel/src/arch/riscv32/boot/entry32.asm

@@ -8,7 +8,7 @@ _start:
     # 1. set sp
     # sp = bootstack + (hartid + 1) * 0x10000
     add     t0, a0, 1
-    slli    t0, t0, 16
+    slli    t0, t0, 14
     lui     sp, %hi(bootstack)
     add     sp, sp, t0
 
@@ -32,7 +32,7 @@ _start:
     .align 12   # page align
     .global bootstack
 bootstack:
-    .space 4096 * 16 * 8
+    .space 4096 * 4 * 8
     .global bootstacktop
 bootstacktop:
 

kernel/src/arch/riscv32/boot/entry64.asm

@@ -8,7 +8,7 @@ _start:
     # 1. set sp
     # sp = bootstack + (hartid + 1) * 0x10000
     add     t0, a0, 1
-    slli    t0, t0, 16
+    slli    t0, t0, 14
     lui     sp, %hi(bootstack)
     add     sp, sp, t0
 
@@ -32,7 +32,7 @@ _start:
     .align 12   # page align
     .global bootstack
 bootstack:
-    .space 4096 * 16 * 8
+    .space 4096 * 4 * 8
     .global bootstacktop
 bootstacktop:
 

kernel/src/memory.rs

@@ -77,7 +77,7 @@ pub fn dealloc_frame(target: usize) {
 }
 
 pub struct KernelStack(usize);
-const STACK_SIZE: usize = 0x8000;
+const STACK_SIZE: usize = 0x4000;
 
 impl KernelStack {
     pub fn new() -> Self {

kernel/src/process/structs.rs

@@ -126,10 +126,8 @@ impl Thread {
     pub unsafe fn new_init() -> Box<Thread> {
         Box::new(Thread {
             context: Context::null(),
-            kstack: KernelStack::new(),
+            // safety: other fields will never be used
-            clear_child_tid: 0,
+            .. core::mem::uninitialized()
-            // safety: this field will never be used
-            proc: core::mem::uninitialized(),
         })
     }