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
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
|
#include "arch/context_switching/main.hpp"
#include "arch/boot/pointers.hpp"
#include "arch/context_switching/syscall_handler.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_global_descriptor_table_register() -> void { kernel::cpu::call(KERNEL_CODE_POINTER); }
} // namespace
auto initialize_descriptor_tables() -> descriptor_tables
{
static bool initalized = false;
if (!initalized)
{
kernel::cpu::clear_interrupt_flag();
segment_descriptor_table::update_global_descriptor_table_register();
interrupt_descriptor_table::update_interrupt_descriptor_table_register();
reload_global_descriptor_table_register();
segment_descriptor_table::update_task_state_segment_register();
kernel::cpu::set_interrupt_flag();
initalized = true;
}
descriptor_tables tables = {segment_descriptor_table::get_or_create_global_descriptor_table(),
interrupt_descriptor_table::get_or_create_interrupt_descriptor_table()};
return tables;
}
auto user_mode_main() -> void
{
kernel::cpu::validate_segment_registers(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR);
asm volatile("SYSCALL");
video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
}
auto switch_to_user_mode() -> void
{
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));
}
auto setup_syscall() -> void
{
uint64_t handler = reinterpret_cast<uint64_t>(syscall_handler);
asm volatile(
/* Write syscall_handler pointer in IA32_LSTAR MSR */
"mov $0xC0000082, %%ecx\n" /* IA32_LSTAR MSR */
"mov %[syscall_handler], %%rax"
"mov %[syscall_handler], %%rdx"
"shr $32, %%rdx\n"
"wrmsr\n"
/* Write RFLAGS Mask in IA32_LSTAR MSR */
"mov $0xC0000084, %%ecx\n" /* IA32_FMASK MSR */
"mov $0x0, %%rax\n" /* RFLAGS Mask lower 32 bits */
"mov $0x0, %%rdx\n" /* RFLAGS Mask upper 32 bits */
"wrmsr\n"
/* Write kernel code segment offset in IA32_STAR MSR */
"mov $0xC0000081, %%ecx\n" /* IA32_STAR MSR */
"mov $0x10, %%rax\n" /* kernel code segment offset lower 32 bits */
"mov $0x0, %%rdx\n" /* kernel code segment offset upper 32 bits */
"wrmsr\n"
/* Set SCE bit in MSR_EFER (enabling syscall instruction)*/
"mov $0xC0000080, %%ecx\n"
"rdmsr\n"
"or $0x1, %%eax\n"
"wrmsr"
: /* no output from call */
: [syscall_handler] "r"(handler));
}
} // namespace teachos::arch::context_switching
|
