From 05e1fedcc9cd30d1a34a65e640da45e980b4f859 Mon Sep 17 00:00:00 2001
From: Marvin Borner
Date: Thu, 19 Sep 2019 19:56:59 +0200
Subject: Moved source to kernel directory
---
src/kernel/gdt/gdt.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 51 insertions(+)
create mode 100644 src/kernel/gdt/gdt.c
(limited to 'src/kernel/gdt/gdt.c')
diff --git a/src/kernel/gdt/gdt.c b/src/kernel/gdt/gdt.c
new file mode 100644
index 0000000..813b432
--- /dev/null
+++ b/src/kernel/gdt/gdt.c
@@ -0,0 +1,51 @@
+struct gdt_entry {
+ unsigned short limit_low;
+ unsigned short base_low;
+ unsigned char base_middle;
+ unsigned char access;
+ unsigned char granularity;
+ unsigned char base_high;
+} __attribute__((packed));
+
+struct gdt_ptr {
+ unsigned short limit;
+ unsigned int base;
+} __attribute__((packed));
+
+struct gdt_entry gdt[3];
+struct gdt_ptr gp;
+
+extern void gdt_flush();
+
+void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran) {
+ // Set descriptor base address
+ gdt[num].base_low = (base & 0xFFFF);
+ gdt[num].base_middle = (base >> 16) & 0xFF;
+ gdt[num].base_high = (base >> 24) & 0xFF;
+
+ // Set descriptor limits
+ gdt[num].limit_low = (limit & 0xFFFF);
+ gdt[num].granularity = ((limit >> 16) & 0x0F);
+
+ // Set granularity and access flags
+ gdt[num].granularity |= (gran & 0xF0);
+ gdt[num].access = access;
+}
+
+void gdt_install() {
+ // Set GDT pointer and limit
+ gp.limit = (sizeof(struct gdt_entry) * 3) - 1;
+ gp.base = &gdt;
+
+ // NULL descriptor
+ gdt_set_gate(0, 0, 0, 0, 0);
+
+ // Code segment
+ gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
+
+ // Data segment
+ gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
+
+ // Remove old GDT and install the new changes!
+ gdt_flush();
+}
\ No newline at end of file
--
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