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#include "arch/context_switching/main.hpp"
#include "arch/boot/pointers.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/msr.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
{
auto constexpr IA32_STAR_ADDRESS = 0xC0000081;
auto constexpr IA32_LSTAR_ADDRESS = 0xC0000082;
auto constexpr IA32_FMASK_ADDRESS = 0xC0000084;
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); }
auto user_mode_main() -> void
{
kernel::cpu::validate_segment_registers(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR);
video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
asm volatile("syscall");
kernel::cpu::validate_segment_registers(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR);
video::vga::text::write("Successfully made a SYSCALL and returned back with SYSRET!",
video::vga::text::common_attributes::green_on_black);
}
auto syscall_handler() -> void
{
uint64_t dummy{};
switch (dummy)
{
case 0:
break;
default:
break;
}
asm volatile("sysretq");
}
auto enable_systemcall() -> void
{
uint64_t const syscall_function = reinterpret_cast<uint64_t>(syscall_handler);
kernel::cpu::write_msr(IA32_LSTAR_ADDRESS, syscall_function);
kernel::cpu::write_msr(IA32_FMASK_ADDRESS, 0U);
uint64_t kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR; // Your 64-bit kernel code segment selector
uint64_t user_cs = USER_CODE_SEGMENT_SELECTOR + 0x3; // User mode code segment selector (RPL=3)
uint64_t star_value = (user_cs << 48) | (kernel_cs << 32);
kernel::cpu::write_msr(IA32_STAR_ADDRESS, star_value);
kernel::cpu::write_msr(IA32_STAR_ADDRESS, KERNEL_CODE_SEGMENT_SELECTOR);
// kernel::cpu::write_msr(IA32_STAR_ADDRESS, KERNEL_CODE_SEGMENT_SELECTOR);
kernel::cpu::set_efer_bit(kernel::cpu::efer_flags::SCE);
}
} // 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 switch_to_user_mode() -> void
{
enable_systemcall();
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
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