zircon/kernel/arch/x86/include/arch/arch_thread.h

// Copyright 2016 The Fuchsia Authors
// Copyright (c) 2009 Corey Tabaka
// Copyright (c) 2015 Intel Corporation
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#ifndef ZIRCON_KERNEL_ARCH_X86_INCLUDE_ARCH_ARCH_THREAD_H_
#define ZIRCON_KERNEL_ARCH_X86_INCLUDE_ARCH_ARCH_THREAD_H_

#include <arch.h>
#include <assert.h>
#include <sys/types.h>
#include <zircon/compiler.h>

#include <arch/kernel_aspace.h>
#include <arch/x86/registers.h>

// Bit 63 of the page_fault_resume field is used to indicate whether a data fault should first
// handle the fault, or immediately return the resume location. The 63'rd bit is selected as this
// bit is invariant over all kernel addresses.
static constexpr uint64_t X86_PFR_RUN_FAULT_HANDLER_BIT = 63;
// Check that the fault handler bit would always be 1 for a kernel address.
static_assert(((KERNEL_ASPACE_BASE >> X86_PFR_RUN_FAULT_HANDLER_BIT) & 1) == 1 &&
                  ((KERNEL_ASPACE_SIZE - 1) & KERNEL_ASPACE_BASE) == 0,
              "PFR fault handler bit not invariant over kernel addresses");

struct arch_thread {
  vaddr_t sp;
#if __has_feature(safe_stack)
  vaddr_t unsafe_sp;
#endif
  vaddr_t fs_base;
  vaddr_t gs_base;

  // Which entry of |suspended_general_regs| to use.
  GeneralRegsSource general_regs_source;

  // Debugger access to userspace general regs while suspended or stopped
  // in an exception. See the description of X86_GENERAL_REGS_* for usage.
  // The regs are saved on the stack and then a pointer is stored here.
  // Nullptr if not suspended or not stopped in an exception.
  // TODO(fxbug.dev/30521): Also nullptr for synthetic exceptions that don't provide
  // them yet.
  union {
    void *gregs;
    syscall_regs_t *syscall;
    iframe_t *iframe;
  } suspended_general_regs;

  // Buffer to save fpu and extended register (e.g., PT) state.
  // xsaves instruction requires the target buffer be 64 byte aligned.
  alignas(64) uint8_t extended_register_buffer[X86_MAX_EXTENDED_REGISTER_SIZE];

  // If non-NULL, address to return to on page fault. Additionally the
  // X86_PFR_RUN_FAULT_HANDLER_BIT controls whether the fault handler is invoked or not. If not
  // invoked resume is called with rdx = fault address and rcx = page fault flags.
  uint64_t page_fault_resume;

  /* |track_debug_state| tells whether the kernel should keep track of the whole debug state for
   * this thread. Normally this is set explicitly by an user that wants to make use of HW
   * breakpoints or watchpoints.
   * |debug_state| will still keep track of the status of the exceptions (DR6), as there are HW
   * exceptions that are triggered without explicit debug state setting (eg. single step).
   *
   * Userspace can still read the complete |debug_state| even if |track_debug_state| is false.
   * As normally the CPU only changes DR6, the |debug_state| will be up to date anyway. */
  bool track_debug_state;
  x86_debug_state_t debug_state;
};

#endif  // ZIRCON_KERNEL_ARCH_X86_INCLUDE_ARCH_ARCH_THREAD_H_