diff options
Diffstat (limited to 'arch/x86_64/src/context_switching')
4 files changed, 133 insertions, 68 deletions
diff --git a/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp b/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp index c041198..7aa0859 100644 --- a/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp +++ b/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp @@ -26,11 +26,6 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table interrupt_descriptor_table.at(i) = {selector, ist, flags, offset}; } - interrupt_descriptor_table.at(0x80) = { - segment_selector{1U, segment_selector::REQUEST_LEVEL_KERNEL}, ist_offset{0U}, - idt_flags{idt_flags::DESCRIPTOR_LEVEL_USER | idt_flags::TRAP_GATE | idt_flags::PRESENT}, - uint64_t{reinterpret_cast<uint64_t>(interrupt_handling::syscall_interrupt_handler)}}; - return interrupt_descriptor_table; } } // namespace diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp index 06c0810..7fe159e 100644 --- a/arch/x86_64/src/context_switching/main.cpp +++ b/arch/x86_64/src/context_switching/main.cpp @@ -1,11 +1,11 @@ #include "arch/context_switching/main.hpp" #include "arch/boot/pointers.hpp" +#include "arch/context_switching/syscall/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/msr.hpp" #include "arch/kernel/cpu/segment_register.hpp" #include "arch/kernel/cpu/tr.hpp" #include "arch/video/vga/text.hpp" @@ -14,10 +14,6 @@ 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, @@ -31,8 +27,6 @@ namespace teachos::arch::context_switching auto user_mode_main() -> void { - video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black); - // RFLAGS is saved into R11, RIP of the next instruction into RCX // Required for SYSRETURN to know where to return too. // Additional state needs to be saved by calling convention: @@ -43,65 +37,16 @@ namespace teachos::arch::context_switching // Actual Source: https://man7.org/linux/man-pages/man2/syscall.2.html More cleare documentation: // https://sys.readthedocs.io/en/latest/doc/05_calling_system_calls.html - uint64_t syscall_number = 60U; - asm volatile("mov %[input], %%rax" - : /* no output from call */ - : [input] "r"(syscall_number) - : "memory"); - asm volatile("syscall"); - - // Reading RAX decrements value by one in 32-bit compatability mode it also crashes vga write, therfore use - // SYSRETQ instead of SYSRET so we do not return into 32-bit compatability mode. - asm volatile("mov %%rax, %[output]" : [output] "=r"(syscall_number)); - video::vga::text::write("Successfully made a SYSCALL and returned with SYSRETQ!", - video::vga::text::common_attributes::green_on_black); - } - auto syscall_handler() -> void - { - uint64_t syscall_number, arg_0, arg_1, arg_2, arg_3, arg_4, arg_5 = {}; - asm volatile("mov %%rax, %[output]" : [output] "=r"(syscall_number)); - asm volatile("mov %%rdi, %[output]" : [output] "=r"(arg_0)); - asm volatile("mov %%rsi, %[output]" : [output] "=r"(arg_1)); - asm volatile("mov %%rdx, %[output]" : [output] "=r"(arg_2)); - asm volatile("mov %%r10, %[output]" : [output] "=r"(arg_3)); - asm volatile("mov %%r8, %[output]" : [output] "=r"(arg_4)); - asm volatile("mov %%r9, %[output]" : [output] "=r"(arg_5)); - - switch (syscall_number) + const char syscall_message[32] = "Successfully entered user mode!"; + auto error = syscall::syscall(syscall::WRITE, {reinterpret_cast<uint64_t>(&syscall_message)}); + + if (!error) { - case 1: - // Write VGA - break; - case 60U: - // Exit - break; - default: - break; + video::vga::text::write("Successfully made a SYSCALL and returned with SYSRETQ!", + video::vga::text::common_attributes::green_on_black); } - - uint64_t result = 0U; - asm volatile("mov %[input], %%rax" - : /* no output from call */ - : [input] "r"(result) - : "memory"); - - 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 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 auto initialize_descriptor_tables() -> descriptor_tables @@ -129,7 +74,7 @@ namespace teachos::arch::context_switching auto switch_to_user_mode() -> void { - enable_systemcall(); + syscall::enable_syscall(); switch_context(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR, user_mode_main); } diff --git a/arch/x86_64/src/context_switching/syscall/main.cpp b/arch/x86_64/src/context_switching/syscall/main.cpp new file mode 100644 index 0000000..e90f503 --- /dev/null +++ b/arch/x86_64/src/context_switching/syscall/main.cpp @@ -0,0 +1,57 @@ +#include "arch/context_switching/syscall/main.hpp" + +#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp" +#include "arch/exception_handling/assert.hpp" +#include "arch/exception_handling/panic.hpp" +#include "arch/kernel/cpu/msr.hpp" + +#include <cstdint> + +namespace teachos::arch::context_switching::syscall +{ + namespace + { + constexpr interrupt_descriptor_table::segment_selector 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); + } + + auto syscall(type syscall_number, arguments args) -> uint64_t + { + 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"); + + uint64_t result{}; + asm volatile("mov %%rax, %[output]" : [output] "=m"(result)); + return result; + } + +} // namespace teachos::arch::context_switching::syscall
\ No newline at end of file diff --git a/arch/x86_64/src/context_switching/syscall/syscall_handler.cpp b/arch/x86_64/src/context_switching/syscall/syscall_handler.cpp new file mode 100644 index 0000000..f6e1c9e --- /dev/null +++ b/arch/x86_64/src/context_switching/syscall/syscall_handler.cpp @@ -0,0 +1,68 @@ +#include "arch/context_switching/syscall/syscall_handler.hpp" + +#include "arch/exception_handling/panic.hpp" +#include "arch/video/vga/text.hpp" + +namespace teachos::arch::context_switching::syscall +{ + + namespace + { + auto write_to_vga_buffer(uint64_t buffer) + { + video::vga::text::write(reinterpret_cast<const char *>(buffer), + video::vga::text::common_attributes::green_on_black); + } + } // 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)); + + switch (static_cast<type>(syscall_number)) + { + case WRITE: + write_to_vga_buffer(arg_0); + break; + default: + teachos::arch::exception_handling::panic("[Syscall Handler] Invalid syscall number"); + break; + } + + uint64_t result = 0U; + asm volatile("mov %[input], %%rax" + : /* no output from call */ + : [input] "m"(result) + : "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"); + + asm volatile("sysretq"); + } + +} // namespace teachos::arch::context_switching::syscall
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