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 #ifndef LLVM_LIBC_SRC___SUPPORT_FILE_LINUX_LSEEKIMPL_H
10 #define LLVM_LIBC_SRC___SUPPORT_FILE_LINUX_LSEEKIMPL_H
11
12 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
13 #include "src/__support/common.h"
14 #include "src/__support/error_or.h"
15 #include "src/errno/libc_errno.h"
16
17 #include <stdint.h> // For uint64_t.
18 #include <sys/syscall.h> // For syscall numbers.
19 #include <unistd.h> // For off_t.
20
21 namespace LIBC_NAMESPACE {
22 namespace internal {
23
lseekimpl(int fd,off_t offset,int whence)24 LIBC_INLINE ErrorOr<off_t> lseekimpl(int fd, off_t offset, int whence) {
25 off_t result;
26 #ifdef SYS_lseek
27 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_lseek, fd, offset, whence);
28 result = ret;
29 #elif defined(SYS_llseek) || defined(SYS__llseek)
30 static_assert(sizeof(size_t) == 4, "size_t must be 32 bits.");
31 #ifdef SYS_llseek
32 constexpr long LLSEEK_SYSCALL_NO = SYS_llseek;
33 #elif defined(SYS__llseek)
34 constexpr long LLSEEK_SYSCALL_NO = SYS__llseek;
35 #endif
36 off_t offset_64 = offset;
37 int ret = LIBC_NAMESPACE::syscall_impl<int>(
38 LLSEEK_SYSCALL_NO, fd, offset_64 >> 32, offset_64, &result, whence);
39 #else
40 #error "lseek, llseek and _llseek syscalls not available."
41 #endif
42 if (ret < 0)
43 return Error(-ret);
44 return result;
45 }
46
47 } // namespace internal
48 } // namespace LIBC_NAMESPACE
49
50 #endif // LLVM_LIBC_SRC___SUPPORT_FILE_LINUX_LSEEKIMPL_H
51