From 7d5a9792e57b4088cce5cc97837eb04016b57a4d Mon Sep 17 00:00:00 2001
From: Marvin Borner
Date: Thu, 31 Oct 2019 00:49:00 +0100
Subject: Implemented basic syscalls and user mode

Doesn't completely work right now
---
 src/kernel/gdt/gdt.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 71 insertions(+), 4 deletions(-)

(limited to 'src/kernel/gdt/gdt.c')

diff --git a/src/kernel/gdt/gdt.c b/src/kernel/gdt/gdt.c
index a4d6a57..b933950 100644
--- a/src/kernel/gdt/gdt.c
+++ b/src/kernel/gdt/gdt.c
@@ -1,4 +1,8 @@
+#include <stdint.h>
+#include <kernel/gdt/gdt.h>
 #include <kernel/system.h>
+#include <kernel/lib/lib.h>
+#include <kernel/io/io.h>
 
 struct gdt_entry {
     unsigned short limit_low;
@@ -14,12 +18,46 @@ struct gdt_ptr {
     void *base;
 } __attribute__((packed));
 
-struct gdt_entry gdt[3];
+struct gdt_entry gdt[6];
 struct gdt_ptr gp;
 
+struct tss_entry_struct {
+    uint32_t prev_tss;
+    uint32_t esp0;
+    uint32_t ss0;
+    uint32_t esp1;
+    uint32_t ss1;
+    uint32_t esp2;
+    uint32_t ss2;
+    uint32_t cr3;
+    uint32_t eip;
+    uint32_t eflags;
+    uint32_t eax;
+    uint32_t ecx;
+    uint32_t edx;
+    uint32_t ebx;
+    uint32_t esp;
+    uint32_t ebp;
+    uint32_t esi;
+    uint32_t edi;
+    uint32_t es;
+    uint32_t cs;
+    uint32_t ss;
+    uint32_t ds;
+    uint32_t fs;
+    uint32_t gs;
+    uint32_t ldt;
+    uint16_t trap;
+    uint16_t iomap_base;
+} __attribute__((packed));
+
+struct tss_entry_struct tss_entry;
+
 extern void gdt_flush();
 
-void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran) {
+extern void tss_flush();
+
+void gdt_set_gate(int32_t num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran) {
     // Set descriptor base address
     gdt[num].base_low = (base & 0xFFFF);
     gdt[num].base_middle = (base >> 16) & 0xFF;
@@ -36,7 +74,7 @@ void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned cha
 
 void gdt_install() {
     // Set GDT pointer and limit
-    gp.limit = (sizeof(struct gdt_entry) * 3) - 1;
+    gp.limit = (sizeof(struct gdt_entry) * 6) - 1;
     gp.base = &gdt;
 
     // NULL descriptor
@@ -48,8 +86,37 @@ void gdt_install() {
     // Data segment
     gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
 
+    // User mode code segment
+    gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);
+
+    // User mode data segment
+    gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);
+
+    // Write TSS
+    tss_write(5, 0x10, 0x0);
+
     // Remove old GDT and install the new changes!
     gdt_flush();
+    tss_flush(); // FAILS
 
     vga_log("Installed Global Descriptor Table", 2);
-}
\ No newline at end of file
+}
+
+void tss_write(int32_t num, uint16_t ss0, uint32_t esp0) {
+    uint32_t base = (uint32_t) &tss_entry;
+    uint32_t limit = base + sizeof(tss_entry);
+
+    gdt_set_gate(num, base, limit, 0xE9, 0x00);
+
+    memset(&tss_entry, 0, sizeof(tss_entry));
+
+    tss_entry.ss0 = ss0;
+    tss_entry.esp0 = esp0;
+
+    tss_entry.cs = 0x0b;
+    tss_entry.ss = tss_entry.ds = tss_entry.es = tss_entry.fs = tss_entry.gs = 0x13;
+}
+
+void set_kernel_stack(uint32_t stack) {
+    tss_entry.esp0 = stack;
+}
-- 
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