glibc/sysdeps/unix/sysv/linux/clone-internal.c

/* The internal wrapper of clone and clone3.
   Copyright (C) 2021-2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library.  If not, see
   <https://www.gnu.org/licenses/>.  */

#include <sysdep.h>
#include <stddef.h>
#include <errno.h>
#include <sched.h>
#include <clone_internal.h>
#include <libc-pointer-arith.h>	/* For cast_to_pointer.  */
#include <stackinfo.h>		/* For _STACK_GROWS_{UP,DOWN}.  */

#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */

#define sizeof_field(TYPE, MEMBER) sizeof ((((TYPE *)0)->MEMBER))
#define offsetofend(TYPE, MEMBER) \
  (offsetof (TYPE, MEMBER) + sizeof_field (TYPE, MEMBER))

_Static_assert (__alignof (struct clone_args) == 8,
		"__alignof (struct clone_args) != 8");
_Static_assert (offsetofend (struct clone_args, tls) == CLONE_ARGS_SIZE_VER0,
		"offsetofend (struct clone_args, tls) != CLONE_ARGS_SIZE_VER0");
_Static_assert (offsetofend (struct clone_args, set_tid_size) == CLONE_ARGS_SIZE_VER1,
		"offsetofend (struct clone_args, set_tid_size) != CLONE_ARGS_SIZE_VER1");
_Static_assert (offsetofend (struct clone_args, cgroup) == CLONE_ARGS_SIZE_VER2,
		"offsetofend (struct clone_args, cgroup) != CLONE_ARGS_SIZE_VER2");
_Static_assert (sizeof (struct clone_args) == CLONE_ARGS_SIZE_VER2,
		"sizeof (struct clone_args) != CLONE_ARGS_SIZE_VER2");

int
__clone_internal_fallback (struct clone_args *cl_args,
			   int (*func) (void *arg), void *arg)
{
  /* Map clone3 arguments to clone arguments.  NB: No need to check
     invalid clone3 specific bits in flags nor exit_signal since this
     is an internal function.  */
  int flags = cl_args->flags | cl_args->exit_signal;
  void *stack = cast_to_pointer (cl_args->stack);
  int ret;

#if !_STACK_GROWS_DOWN && !_STACK_GROWS_UP
# error "Define either _STACK_GROWS_DOWN or _STACK_GROWS_UP"
#endif

#if _STACK_GROWS_DOWN
  stack += cl_args->stack_size;
#endif
  ret = __clone (func, stack, flags, arg,
		 cast_to_pointer (cl_args->parent_tid),
		 cast_to_pointer (cl_args->tls),
		 cast_to_pointer (cl_args->child_tid));
  return ret;
}

int
__clone3_internal (struct clone_args *cl_args, int (*func) (void *args),
		   void *arg)
{
#ifdef HAVE_CLONE3_WRAPPER
# if __ASSUME_CLONE3
  return __clone3 (cl_args, sizeof (*cl_args), func, arg);
# else
  static int clone3_supported = 1;
  if (atomic_load_relaxed (&clone3_supported) == 1)
    {
      int ret = __clone3 (cl_args, sizeof (*cl_args), func, arg);
      if (ret != -1 || errno != ENOSYS)
	return ret;

      atomic_store_relaxed (&clone3_supported, 0);
    }
# endif
#endif
  __set_errno (ENOSYS);
  return -1;
}

int
__clone_internal (struct clone_args *cl_args,
		  int (*func) (void *arg), void *arg)
{
#ifdef HAVE_CLONE3_WRAPPER
  int saved_errno = errno;
  int ret = __clone3_internal (cl_args, func, arg);
  if (ret != -1 || errno != ENOSYS)
    return ret;

  /* NB: Restore errno since errno may be checked against non-zero
     return value.  */
  __set_errno (saved_errno);
#endif

  return __clone_internal_fallback (cl_args, func, arg);
}

libc_hidden_def (__clone_internal)