1//===-- Linux implementation of pwrite ------------------------------------===//
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/pwrite.h"
10
11#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
12#include "src/__support/common.h"
13
14#include "src/__support/libc_errno.h"
15#include "src/__support/macros/config.h"
16#include <stdint.h> // For uint64_t.
17#include <sys/syscall.h> // For syscall numbers.
18
19namespace LIBC_NAMESPACE_DECL {
20
21LLVM_LIBC_FUNCTION(ssize_t, pwrite,
22 (int fd, const void *buf, size_t count, off_t offset)) {
23
24 ssize_t ret;
25 if constexpr (sizeof(long) == sizeof(uint32_t) &&
26 sizeof(off_t) == sizeof(uint64_t)) {
27 // This is a 32-bit system with a 64-bit offset, offset must be split.
28 const uint64_t bits = cpp::bit_cast<uint64_t>(offset);
29 const uint32_t lo = bits & UINT32_MAX;
30 const uint32_t hi = bits >> 32;
31 const long offset_low = cpp::bit_cast<long>(static_cast<long>(lo));
32 const long offset_high = cpp::bit_cast<long>(static_cast<long>(hi));
33 ret = LIBC_NAMESPACE::syscall_impl<ssize_t>(SYS_pwrite64, fd, buf, count,
34 offset_low, offset_high);
35 } else {
36 ret = LIBC_NAMESPACE::syscall_impl<ssize_t>(SYS_pwrite64, fd, buf, count,
37 offset);
38 }
39
40 if (ret < 0) {
41 libc_errno = static_cast<int>(-ret);
42 return -1;
43 }
44 return ret;
45}
46
47} // namespace LIBC_NAMESPACE_DECL
48

source code of libc/src/unistd/linux/pwrite.cpp