From 59ab8c016d0cf5f4ef3ae3a9ef92e437bd384f62 Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Sat, 17 Sep 2022 17:40:35 +0200
Subject: [PATCH] Load a bare-bones TSS for CPU0

---
 kernel/src/gdt/GDT.asm |  5 ++++
 kernel/src/gdt/GDT.cpp | 59 ++++++++++++++++++++++++++++++++++++++----
 2 files changed, 59 insertions(+), 5 deletions(-)

diff --git a/kernel/src/gdt/GDT.asm b/kernel/src/gdt/GDT.asm
index d09b90d7..171debdb 100644
--- a/kernel/src/gdt/GDT.asm
+++ b/kernel/src/gdt/GDT.asm
@@ -13,4 +13,9 @@ load_gdt:
     push rax
     retfq
 .reload_CS:
+    ret
+global load_tr
+load_tr:
+    mov rax, rdi
+    ltr ax
     ret
\ No newline at end of file
diff --git a/kernel/src/gdt/GDT.cpp b/kernel/src/gdt/GDT.cpp
index e2e6bc7c..2b2116f0 100644
--- a/kernel/src/gdt/GDT.cpp
+++ b/kernel/src/gdt/GDT.cpp
@@ -1,7 +1,10 @@
 #define MODULE "gdt"
 
 #include "gdt/GDT.h"
+#include "assert.h"
 #include "log/Log.h"
+#include "memory/KernelMemoryManager.h"
+#include "std/string.h"
 #include <stdint.h>
 
 struct GDTR
@@ -20,28 +23,74 @@ struct GDTEntry
     uint8_t base2;
 } __attribute__((packed));
 
+struct HighGDTEntry
+{
+    uint32_t base_high;
+    uint32_t reserved;
+} __attribute__((packed));
+
+struct TSS
+{
+    uint32_t reserved0;
+    uint64_t rsp[3];
+    uint64_t reserved1;
+    uint64_t ist[7];
+    uint64_t reserved2;
+    uint16_t reserved3;
+    uint16_t iomap_base;
+} __attribute__((packed));
+
 struct InternalGDT
 {
     GDTEntry null;
     GDTEntry kernel_code;
     GDTEntry kernel_data;
-    GDTEntry user_null;
     GDTEntry user_code;
     GDTEntry user_data;
+    GDTEntry tss;
+    HighGDTEntry tss2;
 } __attribute__((packed)) __attribute((aligned(0x1000)));
 
-__attribute__((aligned(0x1000))) static InternalGDT internal_gdt = {
-    {0x0000, 0x0000, 0x00, 0x00, 0x00, 0x00}, {0xffff, 0x0000, 0x00, 0x9a, 0xaf, 0x00},
-    {0xffff, 0x0000, 0x00, 0x92, 0xcf, 0x00}, {0x0000, 0x0000, 0x00, 0x00, 0x00, 0x00},
-    {0xffff, 0x0000, 0x00, 0xfa, 0xaf, 0x00}, {0xffff, 0x0000, 0x00, 0xf2, 0xcf, 0x00}};
+__attribute__((aligned(0x1000))) static InternalGDT internal_gdt = {{0x0000, 0x0000, 0x00, 0x00, 0x00, 0x00},
+                                                                    {0xffff, 0x0000, 0x00, 0x9a, 0xaf, 0x00},
+                                                                    {0xffff, 0x0000, 0x00, 0x92, 0xcf, 0x00},
+                                                                    {0xffff, 0x0000, 0x00, 0xfa, 0xaf, 0x00},
+                                                                    {0xffff, 0x0000, 0x00, 0xf2, 0xcf, 0x00},
+                                                                    {0x0000, 0x0000, 0x00, 0xe9, 0xcf, 0x00},
+                                                                    {0x00000000, 0x00000000}};
+
+static TSS main_tss;
 
 extern "C" void load_gdt(GDTR* gdtr);
+extern "C" void load_tr(int segment);
+
+static void set_base(GDTEntry* entry, uint32_t base)
+{
+    entry->base0 = (base & 0xFFFF);
+    entry->base1 = (base >> 16) & 0xFF;
+    entry->base2 = (base >> 24) & 0xFF;
+}
+
+static void set_limit(GDTEntry* entry, uint32_t limit)
+{
+    ASSERT(limit <= 0xFFFFF);
+    entry->limit0 = limit;
+    entry->limit1_flags = (entry->limit1_flags & 0xF0) | (limit & 0xF);
+}
 
 void GDT::load()
 {
     static GDTR gdtr;
     gdtr.offset = (uint64_t)&internal_gdt;
     gdtr.size = sizeof(InternalGDT);
+    memset(&main_tss, 0, sizeof(TSS));
+    main_tss.rsp[0] =
+        (uint64_t)KernelMemoryManager::get_pages(4) + (4096 * 4) - 8; // allocate 16KB for the syscall stack
+    set_base(&internal_gdt.tss, (uint64_t)&main_tss & 0xffffffff);
+    internal_gdt.tss2.base_high = (uint64_t)&main_tss >> 32;
+    set_limit(&internal_gdt.tss, sizeof(TSS) - 1);
     kdbgln("Loading GDT at offset %lx, size %d", gdtr.offset, gdtr.size);
     load_gdt(&gdtr);
+    kdbgln("Loading TR (GDT entry 0x28)");
+    load_tr(0x28);
 }
\ No newline at end of file