Max OS 0.3
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Public Member Functions | Public Attributes | List of all members
MaxOS::system::GlobalDescriptorTable Class Reference

Sets up the GDT in the CPU. More...

#include <gdt.h>

Public Member Functions

 GlobalDescriptorTable ()
 Construct a new Global Descriptor Table object and set up the GDT entries and load it into the CPU, reloading segment registers.
 
void load ()
 Loads the GDT into the CPU.
 

Public Attributes

uint64_t table [7]
 The GDT entries.
 
gdtr_t gdtr = { }
 The GDTR structure.
 

Detailed Description

Sets up the GDT in the CPU.

Definition at line 53 of file gdt.h.

Constructor & Destructor Documentation

◆ GlobalDescriptorTable()

GlobalDescriptorTable::GlobalDescriptorTable ( )

Construct a new Global Descriptor Table object and set up the GDT entries and load it into the CPU, reloading segment registers.

Definition at line 18 of file gdt.cpp.

19{
20
21 // Null descriptor
22 table[0] = 0;
23
24 // Kernel Code Segment descriptor
25 uint64_t kernel_cs = 0;
26 kernel_cs |= (uint64_t) DescriptorFlags::Write;
27 kernel_cs |= (uint64_t) DescriptorFlags::Execute;
28 kernel_cs |= (uint64_t) DescriptorFlags::CodeOrDataSegment;
29 kernel_cs |= (uint64_t) DescriptorFlags::Present;
30 kernel_cs |= (uint64_t) DescriptorFlags::LongMode;
31 table[1] = kernel_cs;
32
33 // Kernel Data Segment descriptor
34 uint64_t kernel_ds = 0;
35 kernel_ds |= (uint64_t) DescriptorFlags::Write;
36 kernel_ds |= (uint64_t) DescriptorFlags::CodeOrDataSegment;
37 kernel_ds |= (uint64_t) DescriptorFlags::Present;
38 table[2] = kernel_ds;
39
40 // User code segment descriptor (Change the privilege level to 3)
41 uint64_t user_cs = 0;
42 user_cs |= (uint64_t) DescriptorFlags::Write;
43 user_cs |= (uint64_t) DescriptorFlags::Execute;
44 user_cs |= (uint64_t) DescriptorFlags::CodeOrDataSegment;
45 user_cs |= (uint64_t) DescriptorFlags::Present;
46 user_cs |= (uint64_t) DescriptorFlags::LongMode;
47 user_cs |= (3ULL << 45);
48 table[3] = user_cs;
49
50 // User data segment descriptor (Change the privilege level to 3)
51 uint64_t user_ds = 0;
52 user_ds |= (uint64_t) DescriptorFlags::Write;
53 user_ds |= (uint64_t) DescriptorFlags::CodeOrDataSegment;
54 user_ds |= (uint64_t) DescriptorFlags::Present;
55 user_ds |= (3ULL << 45);
56 table[4] = user_ds;
57
58 // Reserve space for the TSS
59 table[5] = 0;
60 table[6] = 0;
61
62 // Load the GDT
63 load();
64
65 // Reload the segment registers
66 asm volatile("mov %0, %%ds" : : "r"(0x10));
67 asm volatile("mov %0, %%es" : : "r"(0x10));
68 asm volatile("mov %0, %%fs" : : "r"(0x10));
69 asm volatile("mov %0, %%gs" : : "r"(0x10));
70 asm volatile("mov %0, %%ss" : : "r"(0x10));
71 Logger::DEBUG() << "Reloaded segment registers\n";
72}
MaxOS::Logger::DEBUG
static Logger DEBUG()
Gets active logger set to DEBUG level.
Definition logger.cpp:193
MaxOS::system::GlobalDescriptorTable::load
void load()
Loads the GDT into the CPU.
Definition gdt.cpp:77
MaxOS::system::GlobalDescriptorTable::table
uint64_t table[7]
The GDT entries.
Definition gdt.h:59

References MaxOS::Logger::DEBUG(), load(), and table.

Member Function Documentation

◆ load()

void GlobalDescriptorTable::load ( )

Loads the GDT into the CPU.

Definition at line 77 of file gdt.cpp.

77 {
78 gdtr = {
79 .size = sizeof(table) - 1,
80 .address = (uint64_t) table,
81 };
82 asm volatile("lgdt %0" : : "m"(gdtr));
83 Logger::DEBUG() << "Loaded GDT of limit 0x" << (uint64_t) gdtr.size << " and address 0x" << (uint64_t) gdtr.address << "\n";
84
85}
MaxOS::system::GlobalDescriptorTable::gdtr
gdtr_t gdtr
The GDTR structure.
Definition gdt.h:61

References MaxOS::Logger::DEBUG(), gdtr, and table.

Referenced by GlobalDescriptorTable().

Member Data Documentation

◆ gdtr

gdtr_t MaxOS::system::GlobalDescriptorTable::gdtr = { }

The GDTR structure.

Definition at line 61 of file gdt.h.

61{ };

Referenced by load().

◆ table

uint64_t MaxOS::system::GlobalDescriptorTable::table[7]

The GDT entries.

Definition at line 59 of file gdt.h.

Referenced by GlobalDescriptorTable(), and load().

The documentation for this class was generated from the following files: