Modifications to support iOS as a development platform

Modules/_ctypes/libffi_ios/closures.c

+/* -----------------------------------------------------------------------
+   closures.c - Copyright (c) 2007, 2009, 2010  Red Hat, Inc.
+                Copyright (C) 2007, 2009, 2010 Free Software Foundation, Inc
+                Copyright (c) 2011 Plausible Labs Cooperative, Inc.
+
+   Code to allocate and deallocate memory for closures.
+
+   Permission is hereby granted, free of charge, to any person obtaining
+   a copy of this software and associated documentation files (the
+   ``Software''), to deal in the Software without restriction, including
+   without limitation the rights to use, copy, modify, merge, publish,
+   distribute, sublicense, and/or sell copies of the Software, and to
+   permit persons to whom the Software is furnished to do so, subject to
+   the following conditions:
+
+   The above copyright notice and this permission notice shall be included
+   in all copies or substantial portions of the Software.
+
+   THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY KIND,
+   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+   NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+   OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+   DEALINGS IN THE SOFTWARE.
+   ----------------------------------------------------------------------- */
+
+#if defined __linux__ && !defined _GNU_SOURCE
+#define _GNU_SOURCE 1
+#endif
+
+#include <fficonfig.h>
+#include <ffi.h>
+#include <ffi_common.h>
+
+#if !FFI_MMAP_EXEC_WRIT && !FFI_EXEC_TRAMPOLINE_TABLE
+# if __gnu_linux__ && !defined(__ANDROID__)
+/* This macro indicates it may be forbidden to map anonymous memory
+   with both write and execute permission.  Code compiled when this
+   option is defined will attempt to map such pages once, but if it
+   fails, it falls back to creating a temporary file in a writable and
+   executable filesystem and mapping pages from it into separate
+   locations in the virtual memory space, one location writable and
+   another executable.  */
+#  define FFI_MMAP_EXEC_WRIT 1
+#  define HAVE_MNTENT 1
+# endif
+# if defined(X86_WIN32) || defined(X86_WIN64) || defined(__OS2__)
+/* Windows systems may have Data Execution Protection (DEP) enabled, 
+   which requires the use of VirtualMalloc/VirtualFree to alloc/free
+   executable memory. */
+#  define FFI_MMAP_EXEC_WRIT 1
+# endif
+#endif
+
+#if FFI_MMAP_EXEC_WRIT && !defined FFI_MMAP_EXEC_SELINUX
+# ifdef __linux__
+/* When defined to 1 check for SELinux and if SELinux is active,
+   don't attempt PROT_EXEC|PROT_WRITE mapping at all, as that
+   might cause audit messages.  */
+#  define FFI_MMAP_EXEC_SELINUX 1
+# endif
+#endif
+
+#if FFI_CLOSURES
+
+#if FFI_EXEC_TRAMPOLINE_TABLE
+
+#ifdef __MACH__
+
+#include <mach/mach.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+extern void *ffi_closure_trampoline_table_page;
+
+typedef struct ffi_trampoline_table ffi_trampoline_table;
+typedef struct ffi_trampoline_table_entry ffi_trampoline_table_entry;
+
+struct ffi_trampoline_table
+{
+  /* contiguous writable and executable pages */
+  vm_address_t config_page;
+  vm_address_t trampoline_page;
+
+  /* free list tracking */
+  uint16_t free_count;
+  ffi_trampoline_table_entry *free_list;
+  ffi_trampoline_table_entry *free_list_pool;
+
+  ffi_trampoline_table *prev;
+  ffi_trampoline_table *next;
+};
+
+struct ffi_trampoline_table_entry
+{
+  void *(*trampoline) ();
+  ffi_trampoline_table_entry *next;
+};
+
+/* Total number of trampolines that fit in one trampoline table */
+#define FFI_TRAMPOLINE_COUNT (PAGE_MAX_SIZE / FFI_TRAMPOLINE_SIZE)
+
+static pthread_mutex_t ffi_trampoline_lock = PTHREAD_MUTEX_INITIALIZER;
+static ffi_trampoline_table *ffi_trampoline_tables = NULL;
+
+static ffi_trampoline_table *
+ffi_trampoline_table_alloc ()
+{
+  ffi_trampoline_table *table = NULL;
+
+  /* Loop until we can allocate two contiguous pages */
+  while (table == NULL)
+    {
+      vm_address_t config_page = 0x0;
+      kern_return_t kt;
+
+      /* Try to allocate two pages */
+      kt =
+        vm_allocate (mach_task_self (), &config_page, PAGE_MAX_SIZE * 2,
+                     VM_FLAGS_ANYWHERE);
+      if (kt != KERN_SUCCESS)
+        {
+          fprintf (stderr, "vm_allocate() failure: %d at %s:%d\n", kt,
+                   __FILE__, __LINE__);
+          break;
+        }
+
+      /* Now drop the second half of the allocation to make room for the trampoline table */
+      vm_address_t trampoline_page = config_page + PAGE_MAX_SIZE;
+      kt = vm_deallocate (mach_task_self (), trampoline_page, PAGE_MAX_SIZE);
+      if (kt != KERN_SUCCESS)
+        {
+          fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
+                   __FILE__, __LINE__);
+          break;
+        }
+
+      /* Remap the trampoline table to directly follow the config page */
+      vm_prot_t cur_prot;
+      vm_prot_t max_prot;
+
+          vm_address_t trampoline_page_template = (vm_address_t)&ffi_closure_trampoline_table_page;
+#ifdef __arm__
+          /* ffi_closure_trampoline_table_page can be thumb-biased on some ARM archs */
+          trampoline_page_template &= ~1UL;
+#endif
+
+      kt =
+        vm_remap (mach_task_self (), &trampoline_page, PAGE_MAX_SIZE, 0x0, FALSE,
+                  mach_task_self (), trampoline_page_template, FALSE,
+                  &cur_prot, &max_prot, VM_INHERIT_SHARE);
+
+      /* If we lost access to the destination trampoline page, drop our config allocation mapping and retry */
+      if (kt != KERN_SUCCESS)
+        {
+          /* Log unexpected failures */
+          if (kt != KERN_NO_SPACE)
+            {
+              fprintf (stderr, "vm_remap() failure: %d at %s:%d\n", kt,
+                       __FILE__, __LINE__);
+            }
+
+          vm_deallocate (mach_task_self (), config_page, PAGE_SIZE);
+          continue;
+        }
+
+      /* We have valid trampoline and config pages */
+      table = calloc (1, sizeof (ffi_trampoline_table));
+      table->free_count = FFI_TRAMPOLINE_COUNT;
+      table->config_page = config_page;
+      table->trampoline_page = trampoline_page;
+
+      /* Create and initialize the free list */
+      table->free_list_pool =
+        calloc (FFI_TRAMPOLINE_COUNT, sizeof (ffi_trampoline_table_entry));
+
+      uint16_t i;
+      for (i = 0; i < table->free_count; i++)
+        {
+          ffi_trampoline_table_entry *entry = &table->free_list_pool[i];
+          entry->trampoline =
+            (void *) (table->trampoline_page + (i * FFI_TRAMPOLINE_SIZE));
+
+          if (i < table->free_count - 1)
+            entry->next = &table->free_list_pool[i + 1];
+        }
+
+      table->free_list = table->free_list_pool;
+    }
+
+  return table;
+}
+
+void *
+ffi_closure_alloc (size_t size, void **code)
+{
+  /* Create the closure */
+  ffi_closure *closure = malloc (size);
+  if (closure == NULL)
+    return NULL;
+
+  pthread_mutex_lock (&ffi_trampoline_lock);
+
+  /* Check for an active trampoline table with available entries. */
+  ffi_trampoline_table *table = ffi_trampoline_tables;
+  if (table == NULL || table->free_list == NULL)
+    {
+      table = ffi_trampoline_table_alloc ();
+      if (table == NULL)
+        {
+          free (closure);
+          return NULL;
+        }
+
+      /* Insert the new table at the top of the list */
+      table->next = ffi_trampoline_tables;
+      if (table->next != NULL)
+        table->next->prev = table;
+
+      ffi_trampoline_tables = table;
+    }
+
+  /* Claim the free entry */
+  ffi_trampoline_table_entry *entry = ffi_trampoline_tables->free_list;
+  ffi_trampoline_tables->free_list = entry->next;
+  ffi_trampoline_tables->free_count--;
+  entry->next = NULL;
+
+  pthread_mutex_unlock (&ffi_trampoline_lock);
+
+  /* Initialize the return values */
+  *code = entry->trampoline;
+  closure->trampoline_table = table;
+  closure->trampoline_table_entry = entry;
+
+  return closure;
+}
+
+void
+ffi_closure_free (void *ptr)
+{
+  ffi_closure *closure = ptr;
+
+  pthread_mutex_lock (&ffi_trampoline_lock);
+
+  /* Fetch the table and entry references */
+  ffi_trampoline_table *table = closure->trampoline_table;
+  ffi_trampoline_table_entry *entry = closure->trampoline_table_entry;
+
+  /* Return the entry to the free list */
+  entry->next = table->free_list;
+  table->free_list = entry;
+  table->free_count++;
+
+  /* If all trampolines within this table are free, and at least one other table exists, deallocate
+   * the table */
+  if (table->free_count == FFI_TRAMPOLINE_COUNT
+      && ffi_trampoline_tables != table)
+    {
+      /* Remove from the list */
+      if (table->prev != NULL)
+        table->prev->next = table->next;
+
+      if (table->next != NULL)
+        table->next->prev = table->prev;
+
+      /* Deallocate pages */
+      kern_return_t kt;
+      kt = vm_deallocate (mach_task_self (), table->config_page, PAGE_SIZE);
+      if (kt != KERN_SUCCESS)
+        fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
+                 __FILE__, __LINE__);
+
+      kt =
+        vm_deallocate (mach_task_self (), table->trampoline_page, PAGE_SIZE);
+      if (kt != KERN_SUCCESS)
+        fprintf (stderr, "vm_deallocate() failure: %d at %s:%d\n", kt,
+                 __FILE__, __LINE__);
+
+      /* Deallocate free list */
+      free (table->free_list_pool);
+      free (table);
+    }
+  else if (ffi_trampoline_tables != table)
+    {
+      /* Otherwise, bump this table to the top of the list */
+      table->prev = NULL;
+      table->next = ffi_trampoline_tables;
+      if (ffi_trampoline_tables != NULL)
+        ffi_trampoline_tables->prev = table;
+
+      ffi_trampoline_tables = table;
+    }
+
+  pthread_mutex_unlock (&ffi_trampoline_lock);
+
+  /* Free the closure */
+  free (closure);
+}
+
+#endif
+
+// Per-target implementation; It's unclear what can reasonable be shared between two OS/architecture implementations.
+
+#elif FFI_MMAP_EXEC_WRIT /* !FFI_EXEC_TRAMPOLINE_TABLE */
+
+#define USE_LOCKS 1
+#define USE_DL_PREFIX 1
+#ifdef __GNUC__
+#ifndef USE_BUILTIN_FFS
+#define USE_BUILTIN_FFS 1
+#endif
+#endif
+
+/* We need to use mmap, not sbrk.  */
+#define HAVE_MORECORE 0
+
+/* We could, in theory, support mremap, but it wouldn't buy us anything.  */
+#define HAVE_MREMAP 0
+
+/* We have no use for this, so save some code and data.  */
+#define NO_MALLINFO 1
+
+/* We need all allocations to be in regular segments, otherwise we
+   lose track of the corresponding code address.  */
+#define DEFAULT_MMAP_THRESHOLD MAX_SIZE_T
+
+/* Don't allocate more than a page unless needed.  */
+#define DEFAULT_GRANULARITY ((size_t)malloc_getpagesize)
+
+#if FFI_CLOSURE_TEST
+/* Don't release single pages, to avoid a worst-case scenario of
+   continuously allocating and releasing single pages, but release
+   pairs of pages, which should do just as well given that allocations
+   are likely to be small.  */
+#define DEFAULT_TRIM_THRESHOLD ((size_t)malloc_getpagesize)
+#endif
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#ifndef _MSC_VER
+#include <unistd.h>
+#endif
+#include <string.h>
+#include <stdio.h>
+#if !defined(X86_WIN32) && !defined(X86_WIN64)
+#ifdef HAVE_MNTENT
+#include <mntent.h>
+#endif /* HAVE_MNTENT */
+#include <sys/param.h>
+#include <pthread.h>
+
+/* We don't want sys/mman.h to be included after we redefine mmap and
+   dlmunmap.  */
+#include <sys/mman.h>
+#define LACKS_SYS_MMAN_H 1
+
+#if FFI_MMAP_EXEC_SELINUX
+#include <sys/statfs.h>
+#include <stdlib.h>
+
+static int selinux_enabled = -1;
+
+static int
+selinux_enabled_check (void)
+{
+  struct statfs sfs;
+  FILE *f;
+  char *buf = NULL;
+  size_t len = 0;
+
+  if (statfs ("/selinux", &sfs) >= 0
+      && (unsigned int) sfs.f_type == 0xf97cff8cU)
+    return 1;
+  f = fopen ("/proc/mounts", "r");
+  if (f == NULL)
+    return 0;
+  while (getline (&buf, &len, f) >= 0)
+    {
+      char *p = strchr (buf, ' ');
+      if (p == NULL)
+        break;
+      p = strchr (p + 1, ' ');
+      if (p == NULL)
+        break;
+      if (strncmp (p + 1, "selinuxfs ", 10) == 0)
+        {
+          free (buf);
+          fclose (f);
+          return 1;
+        }
+    }
+  free (buf);
+  fclose (f);
+  return 0;
+}
+
+#define is_selinux_enabled() (selinux_enabled >= 0 ? selinux_enabled \
+                              : (selinux_enabled = selinux_enabled_check ()))
+
+#else
+
+#define is_selinux_enabled() 0
+
+#endif /* !FFI_MMAP_EXEC_SELINUX */
+
+/* On PaX enable kernels that have MPROTECT enable we can't use PROT_EXEC. */
+#ifdef FFI_MMAP_EXEC_EMUTRAMP_PAX
+#include <stdlib.h>
+
+static int emutramp_enabled = -1;
+
+static int
+emutramp_enabled_check (void)
+{
+  char *buf = NULL;
+  size_t len = 0;
+  FILE *f;
+  int ret;
+  f = fopen ("/proc/self/status", "r");
+  if (f == NULL)
+    return 0;
+  ret = 0;
+
+  while (getline (&buf, &len, f) != -1)
+    if (!strncmp (buf, "PaX:", 4))
+      {
+        char emutramp;
+        if (sscanf (buf, "%*s %*c%c", &emutramp) == 1)
+          ret = (emutramp == 'E');
+        break;
+      }
+  free (buf);
+  fclose (f);
+  return ret;
+}
+
+#define is_emutramp_enabled() (emutramp_enabled >= 0 ? emutramp_enabled \
+                               : (emutramp_enabled = emutramp_enabled_check ()))
+#endif /* FFI_MMAP_EXEC_EMUTRAMP_PAX */
+
+#elif defined (__CYGWIN__) || defined(__INTERIX)
+
+#include <sys/mman.h>
+
+/* Cygwin is Linux-like, but not quite that Linux-like.  */
+#define is_selinux_enabled() 0
+
+#endif /* !defined(X86_WIN32) && !defined(X86_WIN64) */
+
+#ifndef FFI_MMAP_EXEC_EMUTRAMP_PAX
+#define is_emutramp_enabled() 0
+#endif /* FFI_MMAP_EXEC_EMUTRAMP_PAX */
+
+/* Declare all functions defined in dlmalloc.c as static.  */
+static void *dlmalloc(size_t);
+static void dlfree(void*);
+static void *dlcalloc(size_t, size_t) MAYBE_UNUSED;
+static void *dlrealloc(void *, size_t) MAYBE_UNUSED;
+static void *dlmemalign(size_t, size_t) MAYBE_UNUSED;
+static void *dlvalloc(size_t) MAYBE_UNUSED;
+static int dlmallopt(int, int) MAYBE_UNUSED;
+static size_t dlmalloc_footprint(void) MAYBE_UNUSED;
+static size_t dlmalloc_max_footprint(void) MAYBE_UNUSED;
+static void** dlindependent_calloc(size_t, size_t, void**) MAYBE_UNUSED;
+static void** dlindependent_comalloc(size_t, size_t*, void**) MAYBE_UNUSED;
+static void *dlpvalloc(size_t) MAYBE_UNUSED;
+static int dlmalloc_trim(size_t) MAYBE_UNUSED;
+static size_t dlmalloc_usable_size(void*) MAYBE_UNUSED;
+static void dlmalloc_stats(void) MAYBE_UNUSED;
+
+#if !(defined(X86_WIN32) || defined(X86_WIN64) || defined(__OS2__)) || defined (__CYGWIN__) || defined(__INTERIX)
+/* Use these for mmap and munmap within dlmalloc.c.  */
+static void *dlmmap(void *, size_t, int, int, int, off_t);
+static int dlmunmap(void *, size_t);
+#endif /* !(defined(X86_WIN32) || defined(X86_WIN64) || defined(__OS2__)) || defined (__CYGWIN__) || defined(__INTERIX) */
+
+#define mmap dlmmap
+#define munmap dlmunmap
+
+#include "dlmalloc.c"
+
+#undef mmap
+#undef munmap
+
+#if !(defined(X86_WIN32) || defined(X86_WIN64) || defined(__OS2__)) || defined (__CYGWIN__) || defined(__INTERIX)
+
+/* A mutex used to synchronize access to *exec* variables in this file.  */
+static pthread_mutex_t open_temp_exec_file_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+/* A file descriptor of a temporary file from which we'll map
+   executable pages.  */
+static int execfd = -1;
+
+/* The amount of space already allocated from the temporary file.  */
+static size_t execsize = 0;
+
+/* Open a temporary file name, and immediately unlink it.  */
+static int
+open_temp_exec_file_name (char *name, int flags)
+{
+  int fd;
+
+#ifdef HAVE_MKOSTEMP
+  fd = mkostemp (name, flags);
+#else
+  fd = mkstemp (name);
+#endif
+
+  if (fd != -1)
+    unlink (name);
+
+  return fd;
+}
+
+/* Open a temporary file in the named directory.  */
+static int
+open_temp_exec_file_dir (const char *dir)
+{
+  static const char suffix[] = "/ffiXXXXXX";
+  int lendir, flags;
+  char *tempname;
+#ifdef O_TMPFILE
+  int fd;
+#endif
+
+#ifdef O_CLOEXEC
+  flags = O_CLOEXEC;
+#else
+  flags = 0;
+#endif
+
+#ifdef O_TMPFILE
+  fd = open (dir, flags | O_RDWR | O_EXCL | O_TMPFILE, 0700);
+  /* If the running system does not support the O_TMPFILE flag then retry without it. */
+  if (fd != -1 || (errno != EINVAL && errno != EISDIR && errno != EOPNOTSUPP)) {
+    return fd;
+  } else {
+    errno = 0;
+  }
+#endif
+
+  lendir = strlen (dir);
+  tempname = __builtin_alloca (lendir + sizeof (suffix));
+
+  if (!tempname)
+    return -1;
+
+  memcpy (tempname, dir, lendir);
+  memcpy (tempname + lendir, suffix, sizeof (suffix));
+
+  return open_temp_exec_file_name (tempname, flags);
+}
+
+/* Open a temporary file in the directory in the named environment
+   variable.  */
+static int
+open_temp_exec_file_env (const char *envvar)
+{
+  const char *value = getenv (envvar);
+
+  if (!value)
+    return -1;
+
+  return open_temp_exec_file_dir (value);
+}
+
+#ifdef HAVE_MNTENT
+/* Open a temporary file in an executable and writable mount point
+   listed in the mounts file.  Subsequent calls with the same mounts
+   keep searching for mount points in the same file.  Providing NULL
+   as the mounts file closes the file.  */
+static int
+open_temp_exec_file_mnt (const char *mounts)
+{
+  static const char *last_mounts;
+  static FILE *last_mntent;
+
+  if (mounts != last_mounts)
+    {
+      if (last_mntent)
+        endmntent (last_mntent);
+
+      last_mounts = mounts;
+
+      if (mounts)
+        last_mntent = setmntent (mounts, "r");
+      else
+        last_mntent = NULL;
+    }
+
+  if (!last_mntent)
+    return -1;
+
+  for (;;)
+    {
+      int fd;
+      struct mntent mnt;
+      char buf[MAXPATHLEN * 3];
+
+      if (getmntent_r (last_mntent, &mnt, buf, sizeof (buf)) == NULL)
+        return -1;
+
+      if (hasmntopt (&mnt, "ro")
+          || hasmntopt (&mnt, "noexec")
+          || access (mnt.mnt_dir, W_OK))
+        continue;
+
+      fd = open_temp_exec_file_dir (mnt.mnt_dir);
+
+      if (fd != -1)
+        return fd;
+    }
+}
+#endif /* HAVE_MNTENT */
+
+/* Instructions to look for a location to hold a temporary file that
+   can be mapped in for execution.  */
+static struct
+{
+  int (*func)(const char *);
+  const char *arg;
+  int repeat;
+} open_temp_exec_file_opts[] = {
+  { open_temp_exec_file_env, "TMPDIR", 0 },
+  { open_temp_exec_file_dir, "/tmp", 0 },
+  { open_temp_exec_file_dir, "/var/tmp", 0 },
+  { open_temp_exec_file_dir, "/dev/shm", 0 },
+  { open_temp_exec_file_env, "HOME", 0 },
+#ifdef HAVE_MNTENT
+  { open_temp_exec_file_mnt, "/etc/mtab", 1 },
+  { open_temp_exec_file_mnt, "/proc/mounts", 1 },
+#endif /* HAVE_MNTENT */
+};
+
+/* Current index into open_temp_exec_file_opts.  */
+static int open_temp_exec_file_opts_idx = 0;
+
+/* Reset a current multi-call func, then advances to the next entry.
+   If we're at the last, go back to the first and return nonzero,
+   otherwise return zero.  */
+static int
+open_temp_exec_file_opts_next (void)
+{
+  if (open_temp_exec_file_opts[open_temp_exec_file_opts_idx].repeat)
+    open_temp_exec_file_opts[open_temp_exec_file_opts_idx].func (NULL);
+
+  open_temp_exec_file_opts_idx++;
+  if (open_temp_exec_file_opts_idx
+      == (sizeof (open_temp_exec_file_opts)
+          / sizeof (*open_temp_exec_file_opts)))
+    {
+      open_temp_exec_file_opts_idx = 0;
+      return 1;
+    }
+
+  return 0;
+}
+
+/* Return a file descriptor of a temporary zero-sized file in a
+   writable and executable filesystem.  */
+static int
+open_temp_exec_file (void)
+{
+  int fd;
+
+  do
+    {
+      fd = open_temp_exec_file_opts[open_temp_exec_file_opts_idx].func
+        (open_temp_exec_file_opts[open_temp_exec_file_opts_idx].arg);
+
+      if (!open_temp_exec_file_opts[open_temp_exec_file_opts_idx].repeat
+          || fd == -1)
+        {
+          if (open_temp_exec_file_opts_next ())
+            break;
+        }
+    }
+  while (fd == -1);
+
+  return fd;
+}
+
+/* Map in a chunk of memory from the temporary exec file into separate
+   locations in the virtual memory address space, one writable and one
+   executable.  Returns the address of the writable portion, after
+   storing an offset to the corresponding executable portion at the
+   last word of the requested chunk.  */
+static void *
+dlmmap_locked (void *start, size_t length, int prot, int flags, off_t offset)
+{
+  void *ptr;
+
+  if (execfd == -1)
+    {
+      open_temp_exec_file_opts_idx = 0;
+    retry_open:
+      execfd = open_temp_exec_file ();
+      if (execfd == -1)
+        return MFAIL;
+    }
+
+  offset = execsize;
+
+  if (ftruncate (execfd, offset + length))
+    return MFAIL;
+
+  flags &= ~(MAP_PRIVATE | MAP_ANONYMOUS);
+  flags |= MAP_SHARED;
+
+  ptr = mmap (NULL, length, (prot & ~PROT_WRITE) | PROT_EXEC,
+              flags, execfd, offset);
+  if (ptr == MFAIL)
+    {
+      if (!offset)
+        {
+          close (execfd);
+          goto retry_open;
+        }
+      ftruncate (execfd, offset);
+      return MFAIL;
+    }
+  else if (!offset
+           && open_temp_exec_file_opts[open_temp_exec_file_opts_idx].repeat)
+    open_temp_exec_file_opts_next ();
+
+  start = mmap (start, length, prot, flags, execfd, offset);
+
+  if (start == MFAIL)
+    {
+      munmap (ptr, length);
+      ftruncate (execfd, offset);
+      return start;
+    }
+
+  mmap_exec_offset ((char *)start, length) = (char*)ptr - (char*)start;
+
+  execsize += length;
+
+  return start;
+}
+
+/* Map in a writable and executable chunk of memory if possible.
+   Failing that, fall back to dlmmap_locked.  */
+static void *
+dlmmap (void *start, size_t length, int prot,
+        int flags, int fd, off_t offset)
+{
+  void *ptr;
+
+  assert (start == NULL && length % malloc_getpagesize == 0
+          && prot == (PROT_READ | PROT_WRITE)
+          && flags == (MAP_PRIVATE | MAP_ANONYMOUS)
+          && fd == -1 && offset == 0);
+
+#if FFI_CLOSURE_TEST
+  printf ("mapping in %zi\n", length);
+#endif
+
+  if (execfd == -1 && is_emutramp_enabled ())
+    {
+      ptr = mmap (start, length, prot & ~PROT_EXEC, flags, fd, offset);
+      return ptr;
+    }
+
+  if (execfd == -1 && !is_selinux_enabled ())
+    {
+      ptr = mmap (start, length, prot | PROT_EXEC, flags, fd, offset);
+
+      if (ptr != MFAIL || (errno != EPERM && errno != EACCES))
+        /* Cool, no need to mess with separate segments.  */
+        return ptr;
+
+      /* If MREMAP_DUP is ever introduced and implemented, try mmap
+         with ((prot & ~PROT_WRITE) | PROT_EXEC) and mremap with
+         MREMAP_DUP and prot at this point.  */
+    }
+
+  if (execsize == 0 || execfd == -1)
+    {
+      pthread_mutex_lock (&open_temp_exec_file_mutex);
+      ptr = dlmmap_locked (start, length, prot, flags, offset);
+      pthread_mutex_unlock (&open_temp_exec_file_mutex);
+
+      return ptr;
+    }
+
+  return dlmmap_locked (start, length, prot, flags, offset);
+}
+
+/* Release memory at the given address, as well as the corresponding
+   executable page if it's separate.  */
+static int
+dlmunmap (void *start, size_t length)
+{
+  /* We don't bother decreasing execsize or truncating the file, since
+     we can't quite tell whether we're unmapping the end of the file.
+     We don't expect frequent deallocation anyway.  If we did, we
+     could locate pages in the file by writing to the pages being
+     deallocated and checking that the file contents change.
+     Yuck.  */
+  msegmentptr seg = segment_holding (gm, start);
+  void *code;
+
+#if FFI_CLOSURE_TEST
+  printf ("unmapping %zi\n", length);
+#endif
+
+  if (seg && (code = add_segment_exec_offset (start, seg)) != start)
+    {
+      int ret = munmap (code, length);
+      if (ret)
+        return ret;
+    }
+
+  return munmap (start, length);
+}
+
+#if FFI_CLOSURE_FREE_CODE
+/* Return segment holding given code address.  */
+static msegmentptr
+segment_holding_code (mstate m, char* addr)
+{
+  msegmentptr sp = &m->seg;
+  for (;;) {
+    if (addr >= add_segment_exec_offset (sp->base, sp)
+        && addr < add_segment_exec_offset (sp->base, sp) + sp->size)
+      return sp;
+    if ((sp = sp->next) == 0)
+      return 0;
+  }
+}
+#endif
+
+#endif /* !(defined(X86_WIN32) || defined(X86_WIN64) || defined(__OS2__)) || defined (__CYGWIN__) || defined(__INTERIX) */
+
+/* Allocate a chunk of memory with the given size.  Returns a pointer
+   to the writable address, and sets *CODE to the executable
+   corresponding virtual address.  */
+void *
+ffi_closure_alloc (size_t size, void **code)
+{
+  void *ptr;
+
+  if (!code)
+    return NULL;
+
+  ptr = dlmalloc (size);
+
+  if (ptr)
+    {
+      msegmentptr seg = segment_holding (gm, ptr);
+
+      *code = add_segment_exec_offset (ptr, seg);
+    }
+
+  return ptr;
+}
+
+/* Release a chunk of memory allocated with ffi_closure_alloc.  If
+   FFI_CLOSURE_FREE_CODE is nonzero, the given address can be the
+   writable or the executable address given.  Otherwise, only the
+   writable address can be provided here.  */
+void
+ffi_closure_free (void *ptr)
+{
+#if FFI_CLOSURE_FREE_CODE
+  msegmentptr seg = segment_holding_code (gm, ptr);
+
+  if (seg)
+    ptr = sub_segment_exec_offset (ptr, seg);
+#endif
+
+  dlfree (ptr);
+}
+
+
+#if FFI_CLOSURE_TEST
+/* Do some internal sanity testing to make sure allocation and
+   deallocation of pages are working as intended.  */
+int main ()
+{
+  void *p[3];
+#define GET(idx, len) do { p[idx] = dlmalloc (len); printf ("allocated %zi for p[%i]\n", (len), (idx)); } while (0)
+#define PUT(idx) do { printf ("freeing p[%i]\n", (idx)); dlfree (p[idx]); } while (0)
+  GET (0, malloc_getpagesize / 2);
+  GET (1, 2 * malloc_getpagesize - 64 * sizeof (void*));
+  PUT (1);
+  GET (1, 2 * malloc_getpagesize);
+  GET (2, malloc_getpagesize / 2);
+  PUT (1);
+  PUT (0);
+  PUT (2);
+  return 0;
+}
+#endif /* FFI_CLOSURE_TEST */
+# else /* ! FFI_MMAP_EXEC_WRIT */
+
+/* On many systems, memory returned by malloc is writable and
+   executable, so just use it.  */
+
+#include <stdlib.h>
+
+void *
+ffi_closure_alloc (size_t size, void **code)
+{
+  if (!code)
+    return NULL;
+
+  return *code = malloc (size);
+}
+
+void
+ffi_closure_free (void *ptr)
+{
+  free (ptr);
+}
+
+# endif /* ! FFI_MMAP_EXEC_WRIT */
+#endif /* FFI_CLOSURES */