diff options
Diffstat (limited to 'arch/x86_64/pre/src/context_switching')
16 files changed, 599 insertions, 0 deletions
diff --git a/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/gate_descriptor.cpp b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/gate_descriptor.cpp new file mode 100644 index 0000000..28f289c --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/gate_descriptor.cpp @@ -0,0 +1,24 @@ +#include "arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp" + +namespace teachos::arch::context_switching::interrupt_descriptor_table +{ + gate_descriptor::gate_descriptor(uint128_t flags) + : _offset_1(flags) + , _selector(flags >> 19U, flags >> 16U) + , _ist(flags >> 32U) + , _flags(flags >> 40U) + , _offset_2(flags >> 48U) + { + // Nothing to do. + } + + gate_descriptor::gate_descriptor(segment_selector selector, ist_offset ist, idt_flags flags, uint64_t offset) + : _offset_1(offset) + , _selector(selector) + , _ist(ist) + , _flags(flags) + , _offset_2(offset >> 16U) + { + // Nothing to do. + } +} // namespace teachos::arch::context_switching::interrupt_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/idt_flags.cpp b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/idt_flags.cpp new file mode 100644 index 0000000..d36a4c1 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/idt_flags.cpp @@ -0,0 +1,17 @@ +#include "arch/context_switching/interrupt_descriptor_table/idt_flags.hpp" + +namespace teachos::arch::context_switching::interrupt_descriptor_table +{ + idt_flags::idt_flags(uint8_t flags) + : _flags(flags) + { + // Nothing to do. + } + + auto idt_flags::contains_flags(std::bitset<8U> other) const -> bool + { + return (std::bitset<8U>{_flags} & other) == other; + } + + auto idt_flags::operator|=(std::bitset<8U> other) -> void { _flags |= other.to_ulong(); } +} // namespace teachos::arch::context_switching::interrupt_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp new file mode 100644 index 0000000..7aa0859 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp @@ -0,0 +1,53 @@ +#include "arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.hpp" + +#include "arch/exception_handling/assert.hpp" +#include "arch/interrupt_handling/generic_interrupt_handler.hpp" +#include "arch/kernel/cpu/idtr.hpp" + +namespace teachos::arch::context_switching::interrupt_descriptor_table +{ + namespace + { + /// @brief Amount of currently reserved interrupt indicies. + /// See https://wiki.osdev.org/Interrupt_Descriptor_Table#IDT_items for more information. + constexpr uint16_t RESERVED_INTERRUPT_COUNT = 256U; + + auto create_interrupt_descriptor_table() -> interrupt_descriptor_table + { + interrupt_descriptor_table interrupt_descriptor_table{RESERVED_INTERRUPT_COUNT}; + + uint64_t offset = reinterpret_cast<uint64_t>(interrupt_handling::generic_interrupt_handler); + segment_selector selector{1U, segment_selector::REQUEST_LEVEL_KERNEL}; + ist_offset ist{0U}; + idt_flags flags{idt_flags::DESCRIPTOR_LEVEL_KERNEL | idt_flags::INTERRUPT_GATE | idt_flags::PRESENT}; + + for (std::size_t i = 0; i < interrupt_descriptor_table.size(); i++) + { + interrupt_descriptor_table.at(i) = {selector, ist, flags, offset}; + } + + return interrupt_descriptor_table; + } + } // namespace + + auto get_or_create_interrupt_descriptor_table() -> interrupt_descriptor_table & + { + // Interrupt Descriptor Table needs to be kept alive + static interrupt_descriptor_table idt = create_interrupt_descriptor_table(); + return idt; + } + + auto update_interrupt_descriptor_table_register() -> void + { + decltype(auto) idt = get_or_create_interrupt_descriptor_table(); + + interrupt_descriptor_table_pointer idt_pointer{static_cast<uint16_t>((idt.size() * sizeof(gate_descriptor)) - 1), + idt.data()}; + kernel::cpu::load_interrupt_descriptor_table(idt_pointer); + + auto const stored_gdt_pointer = kernel::cpu::store_interrupt_descriptor_table(); + arch::exception_handling::assert( + idt_pointer == stored_gdt_pointer, + "[Interrupt Descriptor Table] Loaded IDTR value is not the same as the stored value."); + } +} // namespace teachos::arch::context_switching::interrupt_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.cpp b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.cpp new file mode 100644 index 0000000..7bcbae6 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.cpp @@ -0,0 +1,13 @@ +#include "arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.hpp" + +namespace teachos::arch::context_switching::interrupt_descriptor_table +{ + interrupt_descriptor_table_pointer::interrupt_descriptor_table_pointer(uint16_t table_length, + gate_descriptor * address) + : table_length(table_length) + , address(address) + { + // Nothing to do. + } + +} // namespace teachos::arch::context_switching::interrupt_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/ist_offset.cpp b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/ist_offset.cpp new file mode 100644 index 0000000..a70e75d --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/ist_offset.cpp @@ -0,0 +1,10 @@ +#include "arch/context_switching/interrupt_descriptor_table/ist_offset.hpp" + +namespace teachos::arch::context_switching::interrupt_descriptor_table +{ + ist_offset::ist_offset(uint8_t index) + : _ist(index) + { + // Nothing to do. + } +} // namespace teachos::arch::context_switching::interrupt_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/segment_selector.cpp b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/segment_selector.cpp new file mode 100644 index 0000000..27f0a3b --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/interrupt_descriptor_table/segment_selector.cpp @@ -0,0 +1,15 @@ +#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp" + +namespace teachos::arch::context_switching::interrupt_descriptor_table +{ + auto segment_selector::contains_flags(std::bitset<3U> other) const -> bool + { + return (std::bitset<3U>{_flags} & other) == other; + } + + auto segment_selector::get_index() const -> uint16_t { return _index; } + + auto segment_selector::operator|=(std::bitset<3U> other) -> void { _flags |= other.to_ulong(); } + + segment_selector::operator uint16_t() const { return *reinterpret_cast<uint16_t const *>(this); } +} // namespace teachos::arch::context_switching::interrupt_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/main.cpp b/arch/x86_64/pre/src/context_switching/main.cpp new file mode 100644 index 0000000..9539428 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/main.cpp @@ -0,0 +1,63 @@ +#include "arch/context_switching/main.hpp" + +#include "arch/boot/pointers.hpp" +#include "arch/context_switching/syscall/syscall_enable.hpp" +#include "arch/kernel/cpu/call.hpp" +#include "arch/kernel/cpu/if.hpp" +#include "arch/kernel/cpu/segment_register.hpp" +#include "arch/kernel/cpu/tr.hpp" +#include "arch/user/main.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); } + } // 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::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 diff --git a/arch/x86_64/pre/src/context_switching/segment_descriptor_table/access_byte.cpp b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/access_byte.cpp new file mode 100644 index 0000000..e31e021 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/access_byte.cpp @@ -0,0 +1,17 @@ +#include "arch/context_switching/segment_descriptor_table/access_byte.hpp" + +namespace teachos::arch::context_switching::segment_descriptor_table +{ + access_byte::access_byte(uint8_t flags) + : _flags(flags) + { + // Nothing to do. + } + + auto access_byte::contains_flags(std::bitset<8U> other) const -> bool + { + return (std::bitset<8U>{_flags} & other) == other; + } + + auto access_byte::operator|=(std::bitset<8U> other) -> void { _flags |= other.to_ulong(); } +} // namespace teachos::arch::context_switching::segment_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/segment_descriptor_table/gdt_flags.cpp b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/gdt_flags.cpp new file mode 100644 index 0000000..e444a24 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/gdt_flags.cpp @@ -0,0 +1,20 @@ +#include "arch/context_switching/segment_descriptor_table/gdt_flags.hpp" + +namespace teachos::arch::context_switching::segment_descriptor_table +{ + gdt_flags::gdt_flags(uint8_t flags, std::bitset<20U> limit) + : _limit_2(limit.to_ulong() >> 16U) + , _flags(flags) + { + // Nothing to do. + } + + auto gdt_flags::contains_flags(std::bitset<4U> other) const -> bool + { + return (std::bitset<4U>{_flags} & other) == other; + } + + auto gdt_flags::get_limit() const -> std::bitset<4U> { return std::bitset<4U>{_limit_2}; } + + auto gdt_flags::operator|=(std::bitset<4U> other) -> void { _flags |= other.to_ulong(); } +} // namespace teachos::arch::context_switching::segment_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp new file mode 100644 index 0000000..bbcee31 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp @@ -0,0 +1,109 @@ +#include "arch/context_switching/segment_descriptor_table/global_descriptor_table.hpp" + +#include "arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp" +#include "arch/exception_handling/assert.hpp" +#include "arch/kernel/cpu/gdtr.hpp" +#include "arch/kernel/cpu/tr.hpp" + +namespace teachos::arch::context_switching::segment_descriptor_table +{ + namespace + { + auto create_segment_descriptor(segment_descriptor_type segment_descriptor_type, access_byte access_level) + -> segment_descriptor_base + { + uint64_t constexpr BASE = 0x0; + std::bitset<20U> constexpr LIMIT{0xFFFFF}; + gdt_flags flags{gdt_flags::GRANULARITY, LIMIT}; + + access_level |= access_byte::PRESENT | access_byte::CODE_OR_DATA_SEGMENT; + if (segment_descriptor_type == segment_descriptor_type::CODE_SEGMENT) + { + flags |= gdt_flags::LONG_MODE; + access_level |= access_byte::CODE_SEGMENT | access_byte::READABLE; + } + else if (segment_descriptor_type == segment_descriptor_type::DATA_SEGMENT) + { + access_level |= access_byte::WRITABLE; + } + + segment_descriptor_base const segment_descriptor_base{access_level, flags, BASE, LIMIT}; + return segment_descriptor_base; + } + + auto create_tss_descriptor(task_state_segment * tss) -> segment_descriptor_extension + { + uint64_t constexpr TSS_LIMIT = sizeof(task_state_segment) - 1; + access_byte const tss_access_byte{access_byte::PRESENT | access_byte::DESCRIPTOR_LEVEL_KERNEL | + access_byte::TASK_STATE_SEGMENT_AVAILABLE}; + gdt_flags const tss_gdt_flags{0U, TSS_LIMIT}; + segment_descriptor_extension const tss_descriptor{tss_access_byte, tss_gdt_flags, reinterpret_cast<uint64_t>(tss), + TSS_LIMIT}; + return tss_descriptor; + } + + auto create_gdt() -> global_descriptor_table + { + segment_descriptor_base const null_segment{0}; + segment_descriptor_base const kernel_code_segment = + create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL); + segment_descriptor_base const kernel_data_segment = + create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_KERNEL); + segment_descriptor_base const user_code_segment = + create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER); + segment_descriptor_base const user_data_segment = + create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_byte::DESCRIPTOR_LEVEL_USER); + + // Task State Segment needs to be kept alive + static auto tss = new task_state_segment(); + segment_descriptor_extension const tss_descriptor = create_tss_descriptor(tss); + + global_descriptor_table global_descriptor_table{null_segment, + kernel_code_segment, + kernel_data_segment, + user_code_segment, + user_data_segment, + tss_descriptor.get_first_gdt_entry(), + tss_descriptor.get_second_gdt_entry()}; + return global_descriptor_table; + } + } // namespace + + auto get_or_create_gdt() -> global_descriptor_table & + { + // Global Descriptor Table needs to be kept alive + static global_descriptor_table gdt = create_gdt(); + return gdt; + } + + auto update_gdtr() -> void + { + decltype(auto) gdt = get_or_create_gdt(); + + // Calculate the size of the gdt in bytes - 1. This subtraction occurs because the maximum value of Size is 65535, + // while the GDT can be up to 65536 bytes in length (8192 entries). Further, no GDT can have a size of 0 bytes. + uint16_t gdt_size = static_cast<uint16_t>((gdt.size() * sizeof(segment_descriptor_base)) - 1); + global_descriptor_table_pointer gdt_pointer{gdt_size, gdt.data()}; + kernel::cpu::load_global_descriptor_table(gdt_pointer); + + auto const stored_gdt_pointer = kernel::cpu::store_global_descriptor_table(); + arch::exception_handling::assert( + gdt_pointer == stored_gdt_pointer, + "[Global Descriptor Table] Loaded GDTR value is not the same as the stored value."); + } + + auto update_tss_register() -> void + { + decltype(auto) gdt = get_or_create_gdt(); + + // Load task state segment descriptor from the last element in the global descriptor table, done by calculating + // offset in bytes to the start of the segment descriptor (5 * 8) = 40 + uint16_t tss_selector = (gdt.size() * sizeof(segment_descriptor_base)) - sizeof(segment_descriptor_extension); + kernel::cpu::load_task_register(tss_selector); + + auto const stored_task_register = kernel::cpu::store_task_register(); + arch::exception_handling::assert(tss_selector == stored_task_register, + "[Global Descriptor Table] Loaded TR value is not the same as the stored value."); + } + +} // namespace teachos::arch::context_switching::segment_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp new file mode 100644 index 0000000..79088b8 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp @@ -0,0 +1,11 @@ +#include "arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp" + +namespace teachos::arch::context_switching::segment_descriptor_table +{ + global_descriptor_table_pointer::global_descriptor_table_pointer(uint16_t table_length, uint64_t * address) + : table_length(table_length) + , address(address) + { + // Nothing to do. + } +} // namespace teachos::arch::context_switching::segment_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/segment_descriptor_table/segment_descriptor_base.cpp b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/segment_descriptor_base.cpp new file mode 100644 index 0000000..04804d9 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/segment_descriptor_base.cpp @@ -0,0 +1,38 @@ +#include "arch/context_switching/segment_descriptor_table/segment_descriptor_base.hpp" + +namespace teachos::arch::context_switching::segment_descriptor_table +{ + segment_descriptor_base::segment_descriptor_base(uint64_t flags) + : _limit_1(flags) + , _base_1(flags >> 16U) + , _access(flags >> 40U) + , _flag(flags >> 52U, flags >> 48U) + , _base_2(flags >> 56U) + { + // Nothing to do. + } + + segment_descriptor_base::segment_descriptor_base(access_byte access_byte, gdt_flags flags, uint32_t base, + std::bitset<20U> limit) + : _limit_1(limit.to_ulong()) + , _base_1(base) + , _access(access_byte) + , _flag(flags) + , _base_2(base >> 24U) + { + // Nothing to do + } + + auto segment_descriptor_base::get_segment_type() const -> segment_descriptor_type + { + if (!_access.contains_flags(access_byte::CODE_OR_DATA_SEGMENT)) + { + return segment_descriptor_type::SYSTEM_SEGMENT; + } + return _access.contains_flags(access_byte::CODE_SEGMENT) ? segment_descriptor_type::CODE_SEGMENT + : segment_descriptor_type::DATA_SEGMENT; + } + + segment_descriptor_base::operator uint64_t() const { return *reinterpret_cast<uint64_t const *>(this); } + +} // namespace teachos::arch::context_switching::segment_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/segment_descriptor_table/segment_descriptor_extension.cpp b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/segment_descriptor_extension.cpp new file mode 100644 index 0000000..a28ec9b --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/segment_descriptor_table/segment_descriptor_extension.cpp @@ -0,0 +1,24 @@ +#include "arch/context_switching/segment_descriptor_table/segment_descriptor_extension.hpp" + +namespace teachos::arch::context_switching::segment_descriptor_table +{ + segment_descriptor_extension::segment_descriptor_extension(uint128_t flags) + : _base(flags) + , _base_3(flags >> 64U) + { + // Nothing to do. + } + + segment_descriptor_extension::segment_descriptor_extension(access_byte access_byte, gdt_flags flags, uint64_t base, + std::bitset<20U> limit) + : _base(access_byte, flags, base, limit) + , _base_3(base >> 32U) + { + // Nothing to do + } + + auto segment_descriptor_extension::get_first_gdt_entry() const -> segment_descriptor_base { return _base; } + + auto segment_descriptor_extension::get_second_gdt_entry() const -> uint64_t { return _base_3; } + +} // namespace teachos::arch::context_switching::segment_descriptor_table diff --git a/arch/x86_64/pre/src/context_switching/syscall/main.cpp b/arch/x86_64/pre/src/context_switching/syscall/main.cpp new file mode 100644 index 0000000..b4ab468 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/syscall/main.cpp @@ -0,0 +1,35 @@ +#include "arch/context_switching/syscall/main.hpp" + +namespace teachos::arch::context_switching::syscall +{ + auto syscall(type syscall_number, arguments args) -> response + { + asm volatile("mov %[input], %%rax" + : /* no output from call */ + : [input] "m"(syscall_number) + : "memory"); + + asm volatile("mov %[input], %%rdi " : /* no output from call */ : [input] "m"(args.arg_0) : "memory"); + asm volatile("mov %[input], %%rsi" : /* no output from call */ : [input] "m"(args.arg_1) : "memory"); + asm volatile("mov %[input], %%rdx" : /* no output from call */ : [input] "m"(args.arg_2) : "memory"); + asm volatile("mov %[input], %%r10" : /* no output from call */ : [input] "m"(args.arg_3) : "memory"); + asm volatile("mov %[input], %%r8" : /* no output from call */ : [input] "m"(args.arg_4) : "memory"); + asm volatile("mov %[input], %%r9" : /* no output from call */ : [input] "m"(args.arg_5) : "memory"); + + asm volatile("syscall"); + + arguments values{}; + asm volatile("mov %%rdi, %[output]" : [output] "=m"(values.arg_0)); + asm volatile("mov %%rsi, %[output]" : [output] "=m"(values.arg_1)); + asm volatile("mov %%rdx, %[output]" : [output] "=m"(values.arg_2)); + asm volatile("mov %%r10, %[output]" : [output] "=m"(values.arg_3)); + asm volatile("mov %%r8, %[output]" : [output] "=m"(values.arg_4)); + asm volatile("mov %%r9, %[output]" : [output] "=m"(values.arg_5)); + + error error_code{}; + asm volatile("mov %%al, %[output]" : [output] "=m"(error_code)); + + return {error_code, values}; + } + +} // namespace teachos::arch::context_switching::syscall diff --git a/arch/x86_64/pre/src/context_switching/syscall/syscall_enable.cpp b/arch/x86_64/pre/src/context_switching/syscall/syscall_enable.cpp new file mode 100644 index 0000000..3c43336 --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/syscall/syscall_enable.cpp @@ -0,0 +1,32 @@ +#include "arch/context_switching/syscall/syscall_enable.hpp" + +#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp" +#include "arch/context_switching/syscall/syscall_handler.hpp" +#include "arch/kernel/cpu/msr.hpp" + +namespace teachos::arch::context_switching::syscall +{ + namespace + { + interrupt_descriptor_table::segment_selector constexpr KERNEL_CODE_SEGMENT_SELECTOR{ + 1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL}; + + auto constexpr IA32_STAR_ADDRESS = 0xC0000081; + auto constexpr IA32_LSTAR_ADDRESS = 0xC0000082; + auto constexpr IA32_FMASK_ADDRESS = 0xC0000084; + + } // namespace + + auto enable_syscall() -> 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 const kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR; + uint64_t const star_value = (kernel_cs << 32) | (kernel_cs << 48); + kernel::cpu::write_msr(IA32_STAR_ADDRESS, star_value); + + kernel::cpu::set_efer_bit(kernel::cpu::efer_flags::SCE); + } +} // namespace teachos::arch::context_switching::syscall diff --git a/arch/x86_64/pre/src/context_switching/syscall/syscall_handler.cpp b/arch/x86_64/pre/src/context_switching/syscall/syscall_handler.cpp new file mode 100644 index 0000000..84dbe5f --- /dev/null +++ b/arch/x86_64/pre/src/context_switching/syscall/syscall_handler.cpp @@ -0,0 +1,118 @@ +#include "arch/context_switching/syscall/syscall_handler.hpp" + +#include "arch/context_switching/syscall/main.hpp" +#include "arch/exception_handling/assert.hpp" +#include "arch/exception_handling/panic.hpp" +#include "arch/memory/heap/global_heap_allocator.hpp" +#include "arch/memory/main.hpp" +#include "arch/video/vga/text.hpp" + +namespace teachos::arch::context_switching::syscall +{ + + namespace + { + auto write_to_vga_buffer(uint64_t buffer) -> response + { + video::vga::text::write(reinterpret_cast<const char *>(buffer), + video::vga::text::common_attributes::green_on_black); + video::vga::text::newline(); + return {error::OK}; + } + + auto expand_user_heap() -> response + { + static auto current_heap_end = memory::heap::USER_HEAP_START; + uint64_t const heap_start = current_heap_end; + memory::remap_heap(heap_start, memory::heap::USER_HEAP_SIZE, memory::paging::entry::USER_ACCESSIBLE); + current_heap_end += memory::heap::USER_HEAP_SIZE; + return {error::OK, {heap_start, memory::heap::USER_HEAP_SIZE}}; + } + } // namespace + + auto syscall_handler() -> void + { + // Saving state of rcx and r11 because it is required by sysretq to function. + // Calls to other functions potentially overwrite these registers, because of + // callee saved calling convention. + uint64_t return_instruction_pointer, rflags = {}; + asm volatile("mov %%rcx, %[output]" : [output] "=m"(return_instruction_pointer)); + asm volatile("mov %%r11, %[output]" : [output] "=m"(rflags)); + + uint64_t syscall_number, arg_0, arg_1, arg_2, arg_3, arg_4, arg_5 = {}; + asm volatile("mov %%rdi, %[output]" : [output] "=m"(arg_0)); + asm volatile("mov %%rsi, %[output]" : [output] "=m"(arg_1)); + asm volatile("mov %%rdx, %[output]" : [output] "=m"(arg_2)); + asm volatile("mov %%r10, %[output]" : [output] "=m"(arg_3)); + asm volatile("mov %%r8, %[output]" : [output] "=m"(arg_4)); + asm volatile("mov %%r9, %[output]" : [output] "=m"(arg_5)); + + // RAX is read last, because paired with our type enum, we can use it to check + // if the register has been written by the compiled code between executing the syscall + // and now. + asm volatile("mov %%rax, %[output]" : [output] "=m"(syscall_number)); + + response result; + switch (static_cast<type>(syscall_number)) + { + case type::WRITE: + result = write_to_vga_buffer(arg_0); + break; + case type::EXPAND_HEAP: + result = expand_user_heap(); + break; + case type::ASSERT: + teachos::arch::exception_handling::assert(arg_0, reinterpret_cast<const char *>(arg_1)); + break; + default: + teachos::arch::exception_handling::panic("[Syscall Handler] Invalid syscall number"); + break; + } + + asm volatile("mov %[input], %%rax" + : /* no output from call */ + : [input] "m"(result.error_code) + : "memory"); + + asm volatile("mov %[input], %%rdi" + : /* no output from call */ + : [input] "m"(result.values.arg_0) + : "memory"); + asm volatile("mov %[input], %%rsi" + : /* no output from call */ + : [input] "m"(result.values.arg_1) + : "memory"); + asm volatile("mov %[input], %%rdx" + : /* no output from call */ + : [input] "m"(result.values.arg_2) + : "memory"); + asm volatile("mov %[input], %%r10" + : /* no output from call */ + : [input] "m"(result.values.arg_3) + : "memory"); + asm volatile("mov %[input], %%r8" + : /* no output from call */ + : [input] "m"(result.values.arg_4) + : "memory"); + asm volatile("mov %[input], %%r9" + : /* no output from call */ + : [input] "m"(result.values.arg_5) + : "memory"); + + asm volatile("mov %[input], %%rcx" + : /* no output from call */ + : [input] "m"(return_instruction_pointer) + : "memory"); + asm volatile("mov %[input], %%r11" + : /* no output from call */ + : [input] "m"(rflags) + : "memory"); + + // Additionally call leave, because x86 allocates stack space for the internal variables. If we do not clean up this + // newly created stack frame the syscall instruction that landed in this syscall_handler, will never return to the + // method that originally called it, because the RIP has not been restored from the previous stack frame. + asm volatile("leave\n" + "sysretq"); + } + +} // namespace teachos::arch::context_switching::syscall |