From ad1167f32b0e1b5d9656539aa22c7c4a8e56d82f Mon Sep 17 00:00:00 2001
From: Baptiste Wicht <baptiste.wicht@gmail.com>
Date: Fri, 5 Aug 2016 12:20:09 +0200
Subject: [PATCH] Transmit tss as early memory

---
 kernel/include/early_memory.hpp |  2 ++
 kernel/include/gdt.hpp          |  4 ++--
 kernel/src/boot/boot_16.cpp     | 14 ++++++--------
 kernel/src/gdt.cpp              |  5 +++++
 kernel/src/scheduler.cpp        |  4 ++--
 5 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/kernel/include/early_memory.hpp b/kernel/include/early_memory.hpp
index c62ef019..45f5acca 100644
--- a/kernel/include/early_memory.hpp
+++ b/kernel/include/early_memory.hpp
@@ -65,4 +65,6 @@ inline void vesa_enabled(bool value){
     *reinterpret_cast<uint32_t*>(vesa_enabled_address) = value ? 1 : 0;
 }
 
+constexpr const uint32_t tss_address = 0x904A0; // 104 bytes (aligned to 128)
+
 #endif
diff --git a/kernel/include/gdt.hpp b/kernel/include/gdt.hpp
index a982b729..c024f2bb 100644
--- a/kernel/include/gdt.hpp
+++ b/kernel/include/gdt.hpp
@@ -105,10 +105,10 @@ struct task_state_segment_t {
     uint16_t io_map_base_address;
 };
 
-extern task_state_segment_t tss;
-
 void flush_tss();
 
+task_state_segment_t& tss();
+
 } //end of namespace gdt
 
 #endif
diff --git a/kernel/src/boot/boot_16.cpp b/kernel/src/boot/boot_16.cpp
index 570a48ce..06d63dac 100644
--- a/kernel/src/boot/boot_16.cpp
+++ b/kernel/src/boot/boot_16.cpp
@@ -10,16 +10,15 @@
 #include "boot/code16gcc.h"
 #include "boot/boot_32.hpp"
 
-#include "gdt.hpp"
+#include "gdt.hpp"  // For the types
 #include "e820.hpp" // For the types
 #include "vesa.hpp" // For the types
 #include "early_memory.hpp"
 
-//The Task State Segment
-gdt::task_state_segment_t gdt::tss;
-
 e820::bios_e820_entry bios_e820_entries[e820::MAX_E820_ENTRIES];
 
+gdt::task_state_segment_t tss; // TODO Remove this (causes relocation errors for now)
+
 namespace {
 
 vesa::vbe_info_block_t vbe_info_block;
@@ -411,7 +410,7 @@ void setup_gdt(){
 
     //2. Init TSS Descriptor
 
-    uint32_t base = reinterpret_cast<uint32_t>(&gdt::tss);
+    uint32_t base = tss_address;;
     uint32_t limit = base + sizeof(gdt::task_state_segment_t);
 
     auto tss_selector = reinterpret_cast<gdt::tss_descriptor_t*>(&gdt[6]);
@@ -441,9 +440,8 @@ void setup_gdt(){
     asm volatile("lgdt [%0]" : : "m" (gdtr));
 
     //5. Zero-out the TSS
-    auto tss_ptr = reinterpret_cast<char*>(&gdt::tss);
-    for(unsigned int i = 0; i < sizeof(gdt::task_state_segment_t); ++i){
-        *tss_ptr++ = 0;
+    for(uint16_t i = 0; i < 128; i += 4){
+        early_write_32(tss_address + i * 4, 0);
     }
 }
 
diff --git a/kernel/src/gdt.cpp b/kernel/src/gdt.cpp
index 33f5c5b3..19f9937f 100644
--- a/kernel/src/gdt.cpp
+++ b/kernel/src/gdt.cpp
@@ -6,7 +6,12 @@
 //=======================================================================
 
 #include "gdt.hpp"
+#include "early_memory.hpp"
 
 void gdt::flush_tss(){
     asm volatile("mov ax, %0; ltr ax;" : : "i" (gdt::TSS_SELECTOR + 0x3) : "rax");
 }
+
+gdt::task_state_segment_t& gdt::tss(){
+    return *reinterpret_cast<task_state_segment_t*>(tss_address);
+}
diff --git a/kernel/src/scheduler.cpp b/kernel/src/scheduler.cpp
index c9b312af..99095bc1 100644
--- a/kernel/src/scheduler.cpp
+++ b/kernel/src/scheduler.cpp
@@ -289,8 +289,8 @@ void switch_to_process(size_t pid){
 
     process.state = scheduler::process_state::RUNNING;
 
-    gdt::tss.rsp0_low = process.process.kernel_rsp & 0xFFFFFFFF;
-    gdt::tss.rsp0_high = process.process.kernel_rsp >> 32;
+    gdt::tss().rsp0_low = process.process.kernel_rsp & 0xFFFFFFFF;
+    gdt::tss().rsp0_high = process.process.kernel_rsp >> 32;
 
     task_switch(old_pid, current_pid);
 }