diff options
Diffstat (limited to 'arch/x86_64')
| -rw-r--r-- | arch/x86_64/include/arch/context_switching/main.hpp | 27 | ||||
| -rw-r--r-- | arch/x86_64/include/arch/kernel/cpu/segment_register.hpp | 80 | ||||
| -rw-r--r-- | arch/x86_64/src/context_switching/main.cpp | 63 | ||||
| -rw-r--r-- | arch/x86_64/src/kernel/cpu/segment_register.cpp | 48 | ||||
| -rw-r--r-- | arch/x86_64/src/kernel/main.cpp | 6 |
5 files changed, 144 insertions, 80 deletions
diff --git a/arch/x86_64/include/arch/context_switching/main.hpp b/arch/x86_64/include/arch/context_switching/main.hpp index e296457..f8477ea 100644 --- a/arch/x86_64/include/arch/context_switching/main.hpp +++ b/arch/x86_64/include/arch/context_switching/main.hpp @@ -16,27 +16,32 @@ namespace teachos::arch::context_switching }; /** - * @brief Setup GDT and IDT TODO + * @brief Creates the Interrupt Descriptor Table and Global Descriptor Table as a static variable the first time this + * method is called and update IDTR and GDTR registers values. * - * @return descriptor_tables + * @note Subsequent calls after the first one, will simply return the previously created tables, but not update the + * registers again. + * + * @return References to the statically created Interrupt Descriptor and Global Descriptor Table. */ auto initialize_descriptor_tables() -> descriptor_tables; /** - * @brief TODO - * - * @param data_segment - * @param code_segment - * @param return_function + * @brief Switches from the current Kernel Mode (Level 0) to User Mode (Level 3). Will simply use predefined Segment + * Selectors for the User Data and User Code Segment, which are Index 3 and 4 in the GDT respectively. */ auto switch_to_user_mode() -> void; /** - * @brief TODO + * @brief Switches from the current Code and Data Segment to the given Code and Data Segment. + * + * @note This method will additionally call initialize_descriptor_tables, to ensure the GDTR and IDTR have been setup + * correctly before attempting to switch the context. This switch is achieved using a far return, which will once + * executed call the given void function. * - * @param data_segment - * @param code_segment - * @param return_function + * @param data_segment Data Segment that the SS, DS; ES, FS and GS register will be set too. + * @param code_segment Code Segment that the CS register will be set too. + * @param return_function Function that will be called once the switch has been achieved. */ auto switch_context(interrupt_descriptor_table::segment_selector data_segment, interrupt_descriptor_table::segment_selector code_segment, void (*return_function)()) -> void; diff --git a/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp b/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp index d495ce6..5c77206 100644 --- a/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp +++ b/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp @@ -6,30 +6,90 @@ namespace teachos::arch::kernel::cpu { /** - * @brief Clear all segment registers. + * @brief Clear all Data Segment registers (DS / ES / FS / GS). */ - [[gnu::naked]] - auto reload_segment_registers() -> void; + auto reload_data_segment_registers() -> void; /** - * @brief Set the value of all segment registers. TODO + * @brief Updates the value of the Data Segment Register (DS), Extra Segment Register (ES), Thread-Local Storage + * Registers (FS / GS). * - * @param segment_selector + * @note The Stack Segment Register (SS) value should also be updated, but the value can not be directly set in + * comparsion to the other registers. This is the case because the register is used for stack management and can not + * be directly changed, instead this has to be done by a special instruction. Therefore + * validate_data_segment_registers should only be called after set_code_segment_register has been called as well. + * + * @param segment_selector Data Segment that should be loaded into the registers. */ - auto set_segment_registers(context_switching::interrupt_descriptor_table::segment_selector segment_selector) -> void; + auto set_data_segment_registers(context_switching::interrupt_descriptor_table::segment_selector segment_selector) + -> void; /** - * @brief Returns the segment_selector in the code segment (cs) register. TODO + * @brief Returns the Segment Selector pointing to the Code Segment that has been loaded into the Code Segment + * Register (CS). + * + * @note The CS register can not be directly changed, instead a Far Return has to be executed to change it * - * @return segment_selector in the cs register + * @return Segment Selector pointing to the currently loaded Code Segment. */ auto read_code_segment_register() -> context_switching::interrupt_descriptor_table::segment_selector; /** - * @brief TODO + * @brief Validates that all Data Segment Registers (DS / ES / FS / GS / SS) are the same as the given Data Segment + * and asserts and stops the application if they are not. + * + * @note This is only the case after set_code_segment_register has been executed as well, because it makes a far + * return that updates the SS register. + * + * @param data_segment Value that should be loaded into all Data Segment Registers. + */ + auto validate_data_segment_registers(context_switching::interrupt_descriptor_table::segment_selector data_segment) + -> void; + + /** + * @brief Validates that the Code Segment Register (CS) is the same as the given Code Segment + * and asserts and stops the application if they are not. + * + * @param code_segment Value that should be loaded into the Code Segment Register. + */ + auto validate_code_segment_register(context_switching::interrupt_descriptor_table::segment_selector code_segment) + -> void; + + /** + * @brief Simply forwards the call to validate_data_segment_registers and validate_code_segment_register and ensures + * that all Segment Registers, have been configured correctly. + * + * @note If all Segment Register have been set correctly the Context Switch using the set_code_segment_register method + * was successfull and the Privilege Level has been changed. + * + * @param data_segment Value that should be loaded into all Data Segment Registers. + * @param code_segment Value that should be loaded into the Code Segment Register. + */ + auto validate_segment_registers(context_switching::interrupt_descriptor_table::segment_selector data_segment, + context_switching::interrupt_descriptor_table::segment_selector code_segment) -> void; + + /** + * @brief Sets the value of the Code Segment Register (CS), this is achieved using a Far Return. + * + * @note The Far Return used by this method, will cause the context to switch, because we are changing from the + * current Code Segment and it's associated Privilege Level to another Code Segment. The given method will then be + * called in the new context and it should be possible to call validate_segment_registers, with the same values + * without assertions if the switch was successful. + * + * To achieve this Far Return we call IRETQ, which expects the stack to be defined a certain way to achieve that we: + * 1. Push the Data Segment Selector + * 2. Push the current Stack Pointer + * 3. Push Eflags + * 4. Push Code Segment Selector + * 5. Push Return Address * + * @param data_segment Data Segment that should be loaded into the SS register. + * @param code_segment Code Segment that should be loaded into the CS register. + * @param address Function that we want to call in the new context created by the given Code Segment. */ - auto validate_data_segment_registers() -> context_switching::interrupt_descriptor_table::segment_selector; + auto set_code_segment_register(context_switching::interrupt_descriptor_table::segment_selector data_segment, + context_switching::interrupt_descriptor_table::segment_selector code_segment, + uint64_t address) -> void; } // namespace teachos::arch::kernel::cpu diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp index 0f2ec93..5cac878 100644 --- a/arch/x86_64/src/context_switching/main.cpp +++ b/arch/x86_64/src/context_switching/main.cpp @@ -12,46 +12,6 @@ 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{ @@ -61,6 +21,14 @@ namespace teachos::arch::context_switching auto initialize_descriptor_tables() -> descriptor_tables { + static bool initalized = false; + if (initalized) + { + descriptor_tables tables = {segment_descriptor_table::get_or_create_global_descriptor_table(), + interrupt_descriptor_table::get_or_create_interrupt_descriptor_table()}; + return tables; + } + kernel::cpu::clear_interrupt_flag(); segment_descriptor_table::update_global_descriptor_table_register(); @@ -68,7 +36,7 @@ namespace teachos::arch::context_switching 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::far_pointer pointer{&kernel::cpu::reload_data_segment_registers, segment_selector}; kernel::cpu::call(pointer); segment_descriptor_table::update_task_state_segment_register(); @@ -77,17 +45,13 @@ namespace teachos::arch::context_switching descriptor_tables tables = {segment_descriptor_table::get_or_create_global_descriptor_table(), interrupt_descriptor_table::get_or_create_interrupt_descriptor_table()}; + initalized = true; 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"); - + 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); } @@ -99,8 +63,9 @@ namespace teachos::arch::context_switching 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)); + (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/src/kernel/cpu/segment_register.cpp b/arch/x86_64/src/kernel/cpu/segment_register.cpp index cb367b6..44b4eff 100644 --- a/arch/x86_64/src/kernel/cpu/segment_register.cpp +++ b/arch/x86_64/src/kernel/cpu/segment_register.cpp @@ -6,7 +6,7 @@ namespace teachos::arch::kernel::cpu { [[gnu::naked]] - auto reload_segment_registers() -> void + auto reload_data_segment_registers() -> void { asm volatile("xor %rax, %rax\n" "mov %rax, %ss\n" @@ -18,7 +18,8 @@ namespace teachos::arch::kernel::cpu } [[gnu::naked]] - auto set_segment_registers(context_switching::interrupt_descriptor_table::segment_selector segment_selector) -> void + auto set_data_segment_registers(context_switching::interrupt_descriptor_table::segment_selector segment_selector) + -> void { asm volatile("xor %%rax, %%rax\n" "mov %[input], %%ax\n" @@ -38,7 +39,8 @@ namespace teachos::arch::kernel::cpu return current_value; } - auto validate_data_segment_registers() -> context_switching::interrupt_descriptor_table::segment_selector + auto validate_data_segment_registers(context_switching::interrupt_descriptor_table::segment_selector data_segment) + -> void { context_switching::interrupt_descriptor_table::segment_selector ss; context_switching::interrupt_descriptor_table::segment_selector ds; @@ -54,10 +56,46 @@ namespace teachos::arch::kernel::cpu "mov %%gs, %[gs_output]\n" : [ss_output] "=r"(ss), [ds_output] "=r"(ds), [es_output] "=r"(es), [fs_output] "=r"(fs), [gs_output] "=r"(gs)); - auto result = ss == ds && ss == es && ss == fs && ss == gs; + auto result = (ss == ds && ss == es && ss == fs && ss == gs); exception_handling::assert(result, "[Segment Register] Values in data register are not the same."); + result = (ss == data_segment); + exception_handling::assert( + result, "[Segment Register] Expected Data Segment is not the same as the value in the Stack Segment register."); + } + + auto validate_code_segment_register(context_switching::interrupt_descriptor_table::segment_selector code_segment) + -> void + { + auto const cs = read_code_segment_register(); + exception_handling::assert( + cs == code_segment, + "[Segment Register] Expected Code Segment is not the same as the value in the Code Segment register."); + } + + auto validate_segment_registers(context_switching::interrupt_descriptor_table::segment_selector data_segment, + context_switching::interrupt_descriptor_table::segment_selector code_segment) -> void + { + validate_data_segment_registers(data_segment); + validate_code_segment_register(code_segment); + } + + [[gnu::naked]] + auto set_code_segment_register(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 %%rsp, %%rax\n" + "push %[data_segment]\n" + "push %%rax\n" + "pushfq\n" + "push %[code_segment]\n" + "mov %[return_function], %%rax\n" + "push %%rax\n" - return ss; + "iretq\n" + : + : [data_segment] "m"(data_segment), [code_segment] "m"(code_segment), [return_function] "r"(address) + : "rax"); } } // namespace teachos::arch::kernel::cpu diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp index b69064d..05c879e 100644 --- a/arch/x86_64/src/kernel/main.cpp +++ b/arch/x86_64/src/kernel/main.cpp @@ -61,11 +61,7 @@ namespace teachos::arch::kernel // stack_overflow_test(0); memory::heap::global_heap_allocator::register_heap_allocator(memory::heap::heap_allocator_type::LINKED_LIST); - - heap_test(); - - decltype(auto) descriptor_tables = context_switching::initialize_descriptor_tables(); - (void)descriptor_tables; + // heap_test(); context_switching::switch_to_user_mode(); } |