zircon/kernel/vm/include/vm/kstack.h

// Copyright 2018 The Fuchsia Authors
//
// 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_VM_INCLUDE_VM_KSTACK_H_
#define ZIRCON_KERNEL_VM_INCLUDE_VM_KSTACK_H_

#include <err.h>
#include <sys/types.h>

__BEGIN_CDECLS

// kstack encapsulates a kernel stack.
//
// kstack must be a C struct because it is embedded in thread_t.
typedef struct kstack {
  vaddr_t base;
  size_t size;
  vaddr_t top;

  // When non-null, |vmar| (and, if safe-stack is enabled, |unsafe_vmar|) points to a ref-counted
  // VmAddressRegion that must be freed via |vm_free_kstack|.
  //
  // Note, the type is void* rather than |fbl::RefPtr| because this struct is used by C code.
  void* vmar;
#if __has_feature(safe_stack)
  vaddr_t unsafe_base;
  // See comment for |vmar|.
  void* unsafe_vmar;
#endif
} kstack_t;

// Allocates a kernel stack with appropriate overrun padding.
//
// Assumes stack has been zero-initialized.
zx_status_t vm_allocate_kstack(kstack_t* stack);

// Frees a stack allocated by |vm_allocate_kstack|.
zx_status_t vm_free_kstack(kstack_t* stack);

__END_CDECLS

#endif  // ZIRCON_KERNEL_VM_INCLUDE_VM_KSTACK_H_