winsup/cygwin/fcntl.cc

   1 /* fcntl.cc: fcntl syscall
   2
   3 This file is part of Cygwin.
   4
   5 This software is a copyrighted work licensed under the terms of the
   6 Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
   7 details. */
   8
   9 #include "winsup.h"
  10 #include <unistd.h>
  11 #include "cygerrno.h"
  12 #include "security.h"
  13 #include "path.h"
  14 #include "fhandler.h"
  15 #include "dtable.h"
  16 #include "cygheap.h"
  17 #include "cygtls.h"
  18
  19 extern "C" int
  20 fcntl (int fd, int cmd, ...)
  21 {
  22   int res = -1;
  23   intptr_t arg = 0;
  24   va_list args;
  25
  26   pthread_testcancel ();
  27
  28   __try
  29     {
  30
  31       debug_printf ("fcntl(%d, %d, ...)", fd, cmd);
  32
  33       /* Don't lock the fd table when performing locking calls. */
  34       cygheap_fdget cfd (fd, cmd < F_GETLK || cmd > F_SETLKW);
  35       if (cfd < 0)
  36         __leave;
  37
  38       /* FIXME?  All numerical args to fcntl are defined as long on Linux.
  39          This relies on a really dirty trick on x86_64:  A 32 bit mov to
  40          a register (e.g. mov $1, %edx) always sets the high 32 bit to 0.
  41          We're following the Linux lead here since the third arg to any
  42          function is in a register anyway (%r8 in MS ABI).  That's the easy
  43          case which is covered here by always reading the arg with
  44          sizeof (intptr_t) == sizeof (long) == sizeof (void*) which matches
  45          all targets.
  46
  47          However, the POSIX standard defines all numerical args as type int.
  48          If we take that literally, we had a (small) problem on 64 bit, since
  49          sizeof (void*) != sizeof (int).  If we would like to follow POSIX more
  50          closely than Linux, we'd have to call va_arg on a per cmd basis. */
  51
  52       va_start (args, cmd);
  53       arg = va_arg (args, intptr_t);
  54       va_end (args);
  55
  56       switch (cmd)
  57         {
  58         case F_DUPFD:
  59         case F_DUPFD_CLOEXEC:
  60           if (arg >= 0 && arg < OPEN_MAX)
  61             {
  62               int flags = cmd == F_DUPFD_CLOEXEC ? O_CLOEXEC : 0;
  63               res = cygheap->fdtab.dup3 (fd, cygheap_fdnew ((arg) - 1), flags);
  64             }
  65           else
  66             {
  67               set_errno (EINVAL);
  68               res = -1;
  69             }
  70           break;
  71         default:
  72           res = cfd->fcntl (cmd, arg);
  73           break;
  74         }
  75     }
  76   __except (EFAULT) {}
  77   __endtry
  78   syscall_printf ("%R = fcntl(%d, %d, %ly)", res, fd, cmd, arg);
  79   return res;
  80 }
  81
  82 EXPORT_ALIAS (fcntl, _fcntl)