libc/src/unistd/linux/lseek.cpp

   1 //===-- Linux implementation of lseek -------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/unistd/lseek.h"
  10 #include "src/errno/libc_errno.h"
  11
  12 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
  13 #include "src/__support/common.h"
  14
  15 #include <sys/syscall.h> // For syscall numbers.
  16 #include <unistd.h>
  17
  18 namespace __llvm_libc {
  19
  20 LLVM_LIBC_FUNCTION(off_t, lseek, (int fd, off_t offset, int whence)) {
  21   off_t result;
  22 #ifdef SYS_lseek
  23   long ret = __llvm_libc::syscall_impl(SYS_lseek, fd, offset, whence);
  24   result = ret;
  25 #elif defined(SYS__llseek)
  26   long ret = __llvm_libc::syscall_impl(SYS__llseek, fd, offset >> 32, offset,
  27                                        &result, whence);
  28 #else
  29 #error "lseek and _llseek syscalls not available."
  30 #endif
  31
  32   if (ret < 0) {
  33     libc_errno = -ret;
  34     return -1;
  35   }
  36   return result;
  37 }
  38
  39 } // namespace __llvm_libc