1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
|
#include "arch/context_switching/main.hpp"
#include "arch/boot/pointers.hpp"
#include "arch/context_switching/syscall/main.hpp"
#include "arch/exception_handling/assert.hpp"
#include "arch/kernel/cpu/call.hpp"
#include "arch/kernel/cpu/control_register.hpp"
#include "arch/kernel/cpu/if.hpp"
#include "arch/kernel/cpu/segment_register.hpp"
#include "arch/kernel/cpu/tr.hpp"
#include "arch/video/vga/text.hpp"
namespace teachos::arch::context_switching
{
namespace
{
constexpr interrupt_descriptor_table::segment_selector KERNEL_CODE_SEGMENT_SELECTOR{
1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
constexpr kernel::cpu::far_pointer KERNEL_CODE_POINTER{&kernel::cpu::reload_data_segment_registers,
KERNEL_CODE_SEGMENT_SELECTOR};
constexpr context_switching::interrupt_descriptor_table::segment_selector USER_CODE_SEGMENT_SELECTOR{
3U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
constexpr context_switching::interrupt_descriptor_table::segment_selector USER_DATA_SEGMENT_SELECTOR{
4U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
auto reload_gdtr() -> void { kernel::cpu::call(KERNEL_CODE_POINTER); }
auto user_mode_main() -> void
{
// RFLAGS is saved into R11, RIP of the next instruction into RCX
// Required for SYSRETURN to know where to return too.
// Additional state needs to be saved by calling convention:
// Syscall Number: RAX, Return Value: RAX (0 indicating no error, and -1 indicating an error, use as a boolean)
// Argument in this order (max 6. no argument on stack): RDI, RSI, RDX, R10, R8, R9
// Not used registers: RBX, RSP, R12, R13, R14
// Actual Source: https://man7.org/linux/man-pages/man2/syscall.2.html More cleare documentation:
// https://sys.readthedocs.io/en/latest/doc/05_calling_system_calls.html
const char syscall_message[32] = "Successfully entered user mode!";
auto error = syscall::syscall(syscall::WRITE, {reinterpret_cast<uint64_t>(&syscall_message)});
if (!error)
{
video::vga::text::write("Successfully made a SYSCALL and returned with SYSRETQ!",
video::vga::text::common_attributes::green_on_black);
}
}
} // namespace
auto initialize_descriptor_tables() -> descriptor_tables
{
static bool initalized = false;
if (!initalized)
{
kernel::cpu::clear_interrupt_flag();
segment_descriptor_table::update_gdtr();
interrupt_descriptor_table::update_interrupt_descriptor_table_register();
reload_gdtr();
segment_descriptor_table::update_tss_register();
kernel::cpu::set_interrupt_flag();
initalized = true;
}
descriptor_tables tables = {segment_descriptor_table::get_or_create_gdt(),
interrupt_descriptor_table::get_or_create_interrupt_descriptor_table()};
return tables;
}
auto switch_to_user_mode() -> void
{
syscall::enable_syscall();
switch_context(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR, user_mode_main);
}
auto switch_context(interrupt_descriptor_table::segment_selector data_segment,
interrupt_descriptor_table::segment_selector code_segment, void (*return_function)()) -> void
{
(void)initialize_descriptor_tables();
kernel::cpu::set_data_segment_registers(data_segment);
kernel::cpu::set_code_segment_register(data_segment, code_segment, reinterpret_cast<uint64_t>(return_function));
}
} // namespace teachos::arch::context_switching
|
