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#include "arch/context_switching/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
{
/**
* @brief Switch context into the mode defined in the segment selectors.
*
* Setup the stack IRETQ expects to switch the mode:
* 1. push data selector
* 2. push current stack pointer
* 3. push eflags
* 4. push code segment selector
* 5. push return address
*
* @param data_segment
* @param code_segment
* @param address
*/
[[gnu::naked]]
auto far_return(context_switching::interrupt_descriptor_table::segment_selector data_segment,
context_switching::interrupt_descriptor_table::segment_selector code_segment, uint64_t address)
-> void
{
asm volatile("mov %[data_segment], %%rax\n"
"mov %%rax, %%ds\n"
"mov %%rax, %%es\n"
"mov %%rax, %%fs\n"
"mov %%rax, %%gs\n"
"mov %%rsp, %%rax\n"
"push %[data_segment]\n"
"push %%rax\n"
"pushfq\n"
"push %[code_segment]\n"
"mov %[return_function], %%rax\n"
"push %%rax\n"
"iretq\n"
:
: [data_segment] "m"(data_segment), [code_segment] "m"(code_segment), [return_function] "r"(address)
: "rax");
}
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};
} // namespace
auto initialize_descriptor_tables() -> descriptor_tables
{
kernel::cpu::clear_interrupt_flag();
segment_descriptor_table::update_global_descriptor_table_register();
interrupt_descriptor_table::update_interrupt_descriptor_table_register();
interrupt_descriptor_table::segment_selector segment_selector{
1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
kernel::cpu::far_pointer pointer{&kernel::cpu::reload_segment_registers, segment_selector};
kernel::cpu::call(pointer);
segment_descriptor_table::update_task_state_segment_register();
kernel::cpu::set_interrupt_flag();
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
{
auto current_segment = kernel::cpu::read_code_segment_register();
exception_handling::assert(USER_CODE_SEGMENT_SELECTOR == current_segment,
"[Context Switching] Context switch into user mode not successful");
exception_handling::assert(USER_DATA_SEGMENT_SELECTOR == kernel::cpu::validate_data_segment_registers(),
"[Context Switching] Context switch into user mode not successful");
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
{
kernel::cpu::set_segment_registers(data_segment);
far_return(data_segment, code_segment, reinterpret_cast<uint64_t>(return_function));
}
} // namespace teachos::arch::context_switching
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