From 8fcd0cf7d6a2c891422c7101840778043207a60d Mon Sep 17 00:00:00 2001
From: Nic Gaffney <gaffney_nic@protonmail.com>
Date: Sun, 10 Dec 2023 09:48:53 -0600
Subject: Changed to the based ASM syntax and implemented a rudementary GDT

---
 src/kernel/gdt.c     | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/kernel/gen_gdt.c | 11 +++++++++++
 src/kernel/kernel.c  | 28 ++++++++++++++--------------
 3 files changed, 76 insertions(+), 14 deletions(-)
 create mode 100644 src/kernel/gdt.c
 create mode 100644 src/kernel/gen_gdt.c

(limited to 'src/kernel')

diff --git a/src/kernel/gdt.c b/src/kernel/gdt.c
new file mode 100644
index 0000000..cf0f487
--- /dev/null
+++ b/src/kernel/gdt.c
@@ -0,0 +1,51 @@
+#include "gdt.h"
+#include <stdint.h>
+
+uint8_t make_access(uint8_t DPL, uint8_t type, uint8_t exec, uint8_t direction,
+                    uint8_t read_write) {
+    uint8_t access = 0;
+    access |= (1 << 7);
+    access |= (DPL << 5);
+    access |= (type << 4);
+    access |= (exec << 3);
+    access |= (direction << 2);
+    access |= (read_write << 1); // 10
+    return access;
+}
+
+uint16_t make_code(uint8_t priv, uint8_t dc, uint8_t rw) {
+    uint16_t access = 0;
+    access |= (1 << 7);
+    access |= (priv << 5);
+    access |= (0b11 << 3);
+    access |= (dc << 2);
+    access |= (rw << 1); // 10
+    access <<= 8;
+    access |= FLAG;
+    return access;
+}
+
+uint16_t make_data(uint8_t priv, uint8_t dc, uint8_t rw) {
+    uint16_t access = 0;
+    access |= (1 << 7);
+    access |= (priv << 5);
+    access |= (0b10 << 3);
+    access |= (dc << 2);
+    access |= (rw << 1); // 10
+    access <<= 8;
+    access |= FLAG;
+    return access;
+}
+
+Segment_Descriptor_t make_descriptor(uint32_t base, uint32_t limit,
+                                     uint16_t access_flag) {
+    uint16_t lim_low = limit;
+    uint16_t base_low = base;
+    uint8_t base_mid = (base >> 16);
+    uint8_t access_byte = access_flag >> 8;
+    uint8_t lim_flag = ((access_flag << 4) | (limit >> 16));
+    uint8_t base_high = (base >> 24);
+    return (Segment_Descriptor_t){
+        lim_low, base_low, base_mid, access_byte, lim_flag, base_high,
+    };
+}
diff --git a/src/kernel/gen_gdt.c b/src/kernel/gen_gdt.c
new file mode 100644
index 0000000..05eedaa
--- /dev/null
+++ b/src/kernel/gen_gdt.c
@@ -0,0 +1,11 @@
+#include "gdt.h"
+
+GDT_t *table = 0x0;
+GDTR_t gdtr = {0, 0};
+void get_gdtr() {
+    *table = (GDT_t){make_descriptor(0, 0, 0),
+                     make_descriptor(0x0000, 0xFFFFF, make_code(0, 0, 1)),
+                     make_descriptor(0x0000, 0xFFFFF, make_data(0, 0, 1))};
+    gdtr.size = sizeof(Segment_Descriptor_t) * 3 - 1;
+    gdtr.offset = 0x0;
+}
diff --git a/src/kernel/kernel.c b/src/kernel/kernel.c
index 40438ec..01c017b 100644
--- a/src/kernel/kernel.c
+++ b/src/kernel/kernel.c
@@ -10,20 +10,20 @@
 #error "Must use ix86-elf compiler"
 #endif
 
-// Color Constants
-
 void kernel_main(void) {
-  print_clear();
-  for (int r = 0; r < 24; r++) {
-    for (int c = 0; c < 80; c += 3) {
-      int color = (r + c) % 15 + 1;
-      print_set_color(color, PRINT_COLOR_BLACK);
-      printf(":3 ");
+    print_clear();
+    for (int r = 0; r < 24; r++) {
+        for (int c = 0; c < 80; c += 3) {
+            int color = (r + c) % 15 + 1;
+            print_set_color(color, PRINT_COLOR_BLACK);
+            printf(":3 ");
+        }
+        printf("%n");
     }
-    printf("%n");
-  }
-  print_set_color(PRINT_COLOR_YELLOW, PRINT_COLOR_BLACK);
-  printf("printf\n\tint: %d\n\tstring: %s\n\tchar: %c\n\tpercent: "
-         "%%\n\tnothing: %n",
-         99, "World! ", 't');
+    print_set_color(PRINT_COLOR_YELLOW, PRINT_COLOR_BLACK);
+    printf("printf\n\tint: %d\n\tstring: %s\n\tchar: %c\n\tpercent: "
+           "%%\n\tnothing: %n",
+           99, "World! ", 't');
+
+    // printf("\n0x%d\n", *((int *)(0x0010)));
 }
-- 
cgit v1.2.3