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Kernel: Implement and use the syscall/sysret instruction pair on x86_64

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Owen Smith 2021-07-23 21:52:25 +01:00 • committed by Andreas Kling
parent d36c84c331
commit e6df1c9988
6 changed files with 169 additions and 1 deletions
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82
Kernel/Arch/x86/x86_64/SyscallEntry.cpp Normal file
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/*
* Copyright (c) 2021, Owen Smith <yeeetari@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <Kernel/Arch/x86/DescriptorTable.h>
#include <Kernel/Arch/x86/Processor.h>
#include <Kernel/Arch/x86/TrapFrame.h>
extern "C" void syscall_entry();
extern "C" [[gnu::naked]] void syscall_entry()
{
// clang-format off
asm(
// Store the user stack, then switch to the kernel stack.
" movq %%rsp, %%gs:%c[user_stack] \n"
" movq %%gs:%c[kernel_stack], %%rsp \n"
// Build RegisterState.
" pushq $0x1b \n" // User ss
" pushq %%gs:%c[user_stack] \n" // User rsp
" sti \n" // It's now safe to enable interrupts, but we can't index into gs after this point
" pushq %%r11 \n" // The CPU preserves the user rflags in r11
" pushq $0x23 \n" // User cs
" pushq %%rcx \n" // The CPU preserves the user IP in rcx
" pushq $0 \n"
" pushq %%r15 \n"
" pushq %%r14 \n"
" pushq %%r13 \n"
" pushq %%r12 \n"
" pushq %%r11 \n"
" pushq %%r10 \n"
" pushq %%r9 \n"
" pushq %%r8 \n"
" pushq %%rax \n"
" pushq %%rcx \n"
" pushq %%rdx \n"
" pushq %%rbx \n"
" pushq %%rsp \n"
" pushq %%rbp \n"
" pushq %%rsi \n"
" pushq %%rdi \n"
" pushq %%rsp \n" // TrapFrame::regs
" subq $" __STRINGIFY(TRAP_FRAME_SIZE - 8) ", %%rsp \n"
" movq %%rsp, %%rdi \n"
" call enter_trap_no_irq \n"
" movq %%rsp, %%rdi \n"
" call syscall_handler \n"
" movq %%rsp, %%rdi \n"
" call exit_trap \n"
" addq $" __STRINGIFY(TRAP_FRAME_SIZE) ", %%rsp \n" // Pop TrapFrame
" popq %%rdi \n"
" popq %%rsi \n"
" popq %%rbp \n"
" addq $8, %%rsp \n" // Skip restoring kernel rsp
" popq %%rbx \n"
" popq %%rdx \n"
" popq %%rcx \n"
" popq %%rax \n"
" popq %%r8 \n"
" popq %%r9 \n"
" popq %%r10 \n"
" popq %%r11 \n"
" popq %%r12 \n"
" popq %%r13 \n"
" popq %%r14 \n"
" popq %%r15 \n"
" addq $8, %%rsp \n"
" popq %%rcx \n"
" addq $16, %%rsp \n"
// Disable interrupts before we restore the user stack pointer. sysret will re-enable interrupts when it restores
// rflags.
" cli \n"
" popq %%rsp \n"
" sysretq \n"
:: [user_stack] "i"(Kernel::Processor::user_stack_offset()), [kernel_stack] "i"(Kernel::Processor::kernel_stack_offset()));
// clang-format on
}