xref: /aosp_15_r20/external/llvm-libc/src/unistd/linux/pwrite.cpp (revision 71db0c75aadcf003ffe3238005f61d7618a3fead)
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/macros/config.h"
15 #include "src/errno/libc_errno.h"
16 #include <stdint.h>      // For uint64_t.
17 #include <sys/syscall.h> // For syscall numbers.
18 
19 namespace LIBC_NAMESPACE_DECL {
20 
21 LLVM_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