diff options
Diffstat (limited to 'arch/x86_64/include')
| -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 |
2 files changed, 86 insertions, 21 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 |