implement fexecve from glibc

include/unistd.h

@@ -585,13 +585,11 @@ extern int execve (const char *__path, char *const __argv[],
 		   char *const __envp[]) __THROW __nonnull ((1, 2));
 libc_hidden_proto(execve)
 
-#if 0 /*def __USE_XOPEN2K8*/
 /* Execute the file FD refers to, overlaying the running program image.
    ARGV and ENVP are passed to the new program, as for `execve'.  */
 extern int fexecve (int __fd, char *const __argv[], char *const __envp[])
      __THROW __nonnull ((2));
-#endif
-
+libc_hidden_proto(fexecve)
 
 /* Execute PATH with arguments ARGV and environment from `environ'.  */
 extern int execv (const char *__path, char *const __argv[])

libc/sysdeps/linux/common/fexecve.c

@@ -0,0 +1,52 @@
+/* Copyright (C) 1994-2019 Free Software Foundation, Inc.
+
+   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 <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+int
+fexecve (int fd, char *const argv[], char *const envp[])
+{
+  if (fd < 0 || argv == NULL || envp == NULL)
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+  /* We use the /proc filesystem to get the information.  If it is not
+     mounted we fail.  */
+  char buf[sizeof "/proc/self/fd/" + sizeof (int) * 3];
+  snprintf (buf, sizeof (buf), "/proc/self/fd/%d", fd);
+
+  /* We do not need the return value.  */
+  execve (buf, argv, envp);
+
+  int save = errno;
+
+  /* We come here only if the 'execve' call fails.  Determine whether
+     /proc is mounted.  If not we return ENOSYS.  */
+  struct stat st;
+  if (stat ("/proc/self/fd", &st) != 0 && errno == ENOENT)
+    save = ENOSYS;
+
+  __set_errno (save);
+
+  return -1;
+}
+libc_hidden_def(fexecve)