From f53f5e4b980f5e2717907010e32e65c4d7f57322 Mon Sep 17 00:00:00 2001
From: Yifan Wu <shinbokuow@163.com>
Date: Sun, 22 Nov 2020 13:05:16 +0800
Subject: [PATCH] Chapter2: Clear .bss inside application.

---
 user/src/bin/01store_fault.rs |  2 +-
 user/src/lib.rs               | 10 ++++++++++
 user/src/linker.ld            |  2 ++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/user/src/bin/01store_fault.rs b/user/src/bin/01store_fault.rs
index 7f02ae8e..790196b2 100644
--- a/user/src/bin/01store_fault.rs
+++ b/user/src/bin/01store_fault.rs
@@ -7,7 +7,7 @@ extern crate user_lib;
 
 #[no_mangle]
 fn main() -> i32 {
-    println!("Into Test store_fault, we will insert an invalid store behavior...");
+    println!("Into Test store_fault, we will insert an invalid store operation...");
     println!("Kernel should kill this application!");
     unsafe { (0x0 as *mut u8).write_volatile(0); }
     0
diff --git a/user/src/lib.rs b/user/src/lib.rs
index c905e412..ed7ba84c 100644
--- a/user/src/lib.rs
+++ b/user/src/lib.rs
@@ -11,6 +11,7 @@ mod lang_items;
 #[no_mangle]
 #[link_section = ".text.entry"]
 pub extern "C" fn _start() -> ! {
+    clear_bss();
     syscall::sys_exit(main());
     panic!("unreachable after sys_exit!");
 }
@@ -21,3 +22,12 @@ fn main() -> i32 {
     panic!("Cannot find main!");
 }
 
+fn clear_bss() {
+    extern "C" {
+        fn start_bss();
+        fn end_bss();
+    }
+    (start_bss as usize..end_bss as usize).for_each(|addr| {
+        unsafe { (addr as *mut u8).write_volatile(0); }
+    });
+}
\ No newline at end of file
diff --git a/user/src/linker.ld b/user/src/linker.ld
index 40db14a2..cbf7486e 100644
--- a/user/src/linker.ld
+++ b/user/src/linker.ld
@@ -17,7 +17,9 @@ SECTIONS
         *(.data .data.*)
     }
     .bss : {
+        start_bss = .;
         *(.bss .bss.*)
+        end_bss = .;
     }
     /DISCARD/ : {
         *(.eh_frame)