From 4b017882af9a2919ea9777461714e60e51c4321b Mon Sep 17 00:00:00 2001
From: zhangxinyu <840317537@qq.com>
Date: Wed, 17 May 2023 14:08:01 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=E7=94=A8=E6=88=B7=E7=A8=8B?=
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---
 ch2/user/src/bin/00hello_world.rs |  3 ++-
 ch2/user/src/lib.rs               | 29 +++++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/ch2/user/src/bin/00hello_world.rs b/ch2/user/src/bin/00hello_world.rs
index 965827b..6995fb6 100644
--- a/ch2/user/src/bin/00hello_world.rs
+++ b/ch2/user/src/bin/00hello_world.rs
@@ -4,6 +4,7 @@
 use user_lib::*;
 
 #[no_mangle]
-fn main() {
+fn main() -> i32 {
     println!("123");
+    0
 }
\ No newline at end of file
diff --git a/ch2/user/src/lib.rs b/ch2/user/src/lib.rs
index e859d12..23b813a 100644
--- a/ch2/user/src/lib.rs
+++ b/ch2/user/src/lib.rs
@@ -2,12 +2,37 @@
 #![feature(linkage)]  // 开启弱链接特性
 #![feature(panic_info_message)]
 
-pub mod syscall;
+
 pub mod user_lang_items;
 pub use user_lang_items::*;
 
+pub mod syscall;
+use syscall::{sys_exit};
+
+extern "C" {
+    fn start_bss();
+    fn end_bss();
+}
+
+
+// 只要使用这个包, 那么这里就会作为bin程序的开始
+#[no_mangle]
+#[link_section = ".text.entry"]  // 链接到指定的段
+pub extern "C" fn _start() -> ! {
+    clear_bss();
+    sys_exit(main());  // 这里执行的main程序是我们 bin文件夹里面的main, 而不是下面的, 下面的main程序只有在bin程序没有main函数的时候才会链接
+    // 正常是不会走到这一步的, 因为上面已经退出了程序
+    panic!("unreachable after sys_exit!");
+}
+
 #[linkage = "weak"]  // 设置我们默认的main函数, 弱链接
 #[no_mangle]
 fn main() -> i32 {
     panic!("Cannot find main!");
-}
\ No newline at end of file
+}
+
+fn clear_bss() {
+    unsafe {
+        (start_bss as usize..end_bss as usize).for_each(|p| (p as *mut u8).write_unaligned(0))
+    };
+}