1  /* Linux lseek implementation, 32 bits off_t.
       2     Copyright (C) 2016-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library.  If not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <unistd.h>
      20  #include <stdint.h>
      21  #include <sys/types.h>
      22  #include <sysdep.h>
      23  #include <errno.h>
      24  
      25  #ifndef __OFF_T_MATCHES_OFF64_T
      26  
      27  /* Test for overflows of structures where we ask the kernel to fill them
      28     in with standard 64-bit syscalls but return them through APIs that
      29     only expose the low 32 bits of some fields.  */
      30  
      31  static inline off_t lseek_overflow (loff_t res)
      32  {
      33    off_t retval = (off_t) res;
      34    if (retval == res)
      35      return retval;
      36  
      37    __set_errno (EOVERFLOW);
      38    return (off_t) -1;
      39  }
      40  
      41  off_t
      42  __lseek (int fd, off_t offset, int whence)
      43  {
      44  #ifdef __NR_llseek
      45  # define __NR__llseek __NR_llseek
      46  #endif
      47  
      48  # ifdef __NR__llseek
      49    loff_t res;
      50    int rc = INLINE_SYSCALL_CALL (_llseek, fd,
      51  				(long) (((uint64_t) (offset)) >> 32),
      52  				(long) offset, &res, whence);
      53    return rc ?: lseek_overflow (res);
      54  # else
      55    return INLINE_SYSCALL_CALL (lseek, fd, offset, whence);
      56  # endif
      57  }
      58  libc_hidden_def (__lseek)
      59  weak_alias (__lseek, lseek)
      60  strong_alias (__lseek, __libc_lseek)
      61  #endif /* __OFF_T_MATCHES_OFF64_T  */