1//===-- Linux implementation of pread -------------------------------------===//
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/pread.h"
10
11#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
12#include "src/__support/common.h"
13#include "src/__support/macros/sanitizer.h" // for MSAN_UNPOISON
14#include "src/errno/libc_errno.h"
15#include <stdint.h> // For uint64_t.
16#include <sys/syscall.h> // For syscall numbers.
17
18namespace LIBC_NAMESPACE {
19
20LLVM_LIBC_FUNCTION(ssize_t, pread,
21 (int fd, void *buf, size_t count, off_t offset)) {
22#ifdef LIBC_TARGET_ARCH_IS_RISCV32
23 static_assert(sizeof(off_t) == 8);
24 ssize_t ret = LIBC_NAMESPACE::syscall_impl<ssize_t>(
25 SYS_pread64, fd, buf, count, (long)offset,
26 (long)(((uint64_t)(offset)) >> 32));
27#else
28 ssize_t ret = LIBC_NAMESPACE::syscall_impl<ssize_t>(SYS_pread64, ts: fd, ts: buf,
29 ts: count, ts: offset);
30#endif
31 // The cast is important since there is a check that dereferences the pointer
32 // which fails on void*.
33 MSAN_UNPOISON(reinterpret_cast<char *>(buf), count);
34 if (ret < 0) {
35 libc_errno = static_cast<int>(-ret);
36 return -1;
37 }
38 return ret;
39}
40
41} // namespace LIBC_NAMESPACE
42

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