From bed09d05189683abedb23062d54359707adfa9ca Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jackpot51@gmail.com>
Date: Sun, 11 Sep 2016 18:25:05 -0600
Subject: [PATCH] Allow thread control block to be moved

---
 arch/x86_64/src/paging/mod.rs | 13 +++++++++----
 arch/x86_64/src/start.rs      | 15 ++++-----------
 2 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/arch/x86_64/src/paging/mod.rs b/arch/x86_64/src/paging/mod.rs
index fd02184..8dc9975 100644
--- a/arch/x86_64/src/paging/mod.rs
+++ b/arch/x86_64/src/paging/mod.rs
@@ -1,6 +1,7 @@
 //! # Paging
 //! Some code was borrowed from [Phil Opp's Blog](http://os.phil-opp.com/modifying-page-tables.html)
 
+use core::mem;
 use core::ops::{Deref, DerefMut};
 use x86::{msr, tlb};
 
@@ -22,7 +23,9 @@ pub const ENTRY_COUNT: usize = 512;
 pub const PAGE_SIZE: usize = 4096;
 
 /// Initialize paging
-pub unsafe fn init(stack_start: usize, stack_end: usize) -> ActivePageTable {
+///
+/// Returns page table and thread control block offset
+pub unsafe fn init(stack_start: usize, stack_end: usize) -> (ActivePageTable, usize) {
     extern {
         /// The starting byte of the text (code) data segment.
         static mut __text_start: u8;
@@ -145,9 +148,11 @@ pub unsafe fn init(stack_start: usize, stack_end: usize) -> ActivePageTable {
     }
 
     // Map and clear TBSS
+    let tcb_offset;
     {
         let start = & __tbss_start as *const _ as usize;
         let end = & __tbss_end as *const _ as usize;
+        tcb_offset = end - mem::size_of::<usize>();
         if end > start {
             let start_page = Page::containing_address(VirtualAddress::new(start));
             let end_page = Page::containing_address(VirtualAddress::new(end - 1));
@@ -157,13 +162,13 @@ pub unsafe fn init(stack_start: usize, stack_end: usize) -> ActivePageTable {
                 ::externs::memset(page.start_address().get() as *mut u8, 0, 4096);
             }
 
-            *(end as *mut usize).offset(-1) = end;
+            *(tcb_offset as *mut usize) = end;
         }
     }
 
     active_table.flush_all();
 
-    active_table
+    (active_table, tcb_offset)
 }
 
 pub struct ActivePageTable {
@@ -217,7 +222,7 @@ impl ActivePageTable {
         where F: FnOnce(&mut Mapper)
     {
         use x86::controlregs;
-        
+
         {
             let backup = Frame::containing_address(PhysicalAddress::new(unsafe { controlregs::cr3() } as usize));
 
diff --git a/arch/x86_64/src/start.rs b/arch/x86_64/src/start.rs
index 566f696..72d5280 100644
--- a/arch/x86_64/src/start.rs
+++ b/arch/x86_64/src/start.rs
@@ -47,8 +47,6 @@ pub unsafe extern fn kstart() -> ! {
             static mut __bss_start: u8;
             /// The ending byte of the _.bss_ (uninitialized data) segment.
             static mut __bss_end: u8;
-            /// The end of the tbss.
-            static mut __tbss_end: u8;
             /// The end of the kernel
             static mut __end: u8;
         }
@@ -75,10 +73,10 @@ pub unsafe extern fn kstart() -> ! {
         let stack_end = 0x0009F000;
 
         // Initialize paging
-        let mut active_table = paging::init(stack_start, stack_end);
+        let (mut active_table, tcb_offset) = paging::init(stack_start, stack_end);
 
         // Set up GDT
-        gdt::init((&__tbss_end as *const u8 as *const usize).offset(-1) as usize, stack_end);
+        gdt::init(tcb_offset, stack_end);
 
         // Set up IDT
         idt::init();
@@ -140,19 +138,14 @@ pub unsafe extern fn kstart() -> ! {
 /// Entry to rust for an AP
 pub unsafe extern fn kstart_ap(stack_start: usize, stack_end: usize) -> ! {
     {
-        extern {
-            /// The end of the tbss.
-            static mut __tbss_end: u8;
-        }
-
         assert_eq!(BSS_TEST_ZERO, 0);
         assert_eq!(DATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFF);
 
         // Initialize paging
-        let mut active_table = paging::init(stack_start, stack_end);
+        let (mut active_table, tcb_offset) = paging::init(stack_start, stack_end);
 
         // Set up GDT for AP
-        gdt::init_ap((&__tbss_end as *const u8 as *const usize).offset(-1) as usize, stack_end);
+        gdt::init_ap(tcb_offset, stack_end);
 
         // Set up IDT for AP
         idt::init();