1//===-- Linux implementation of getentropy --------------------------------===//
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/getentropy.h"
10#include "hdr/errno_macros.h"
11#include "src/__support/OSUtil/syscall.h"
12#include "src/__support/common.h"
13#include "src/__support/libc_errno.h"
14
15#include <sys/syscall.h> // For syscall numbers.
16
17namespace LIBC_NAMESPACE_DECL {
18LLVM_LIBC_FUNCTION(int, getentropy, (void *buffer, size_t length)) {
19 // check the length limit
20 if (length > 256) {
21 libc_errno = EIO;
22 return -1;
23 }
24
25 char *cursor = static_cast<char *>(buffer);
26 while (length != 0) {
27 // 0 flag means urandom and blocking, which meets the assumption of
28 // getentropy
29 auto ret = syscall_impl<long>(SYS_getrandom, cursor, length, 0);
30
31 // on success, advance the buffer pointer
32 if (ret >= 0) {
33 length -= static_cast<size_t>(ret);
34 cursor += ret;
35 continue;
36 }
37
38 auto error = -static_cast<int>(ret);
39
40 // on EINTR, try again
41 if (error == EINTR)
42 continue;
43
44 // on ENOSYS, forward errno and exit;
45 // otherwise, set EIO and exit
46 libc_errno = (error == ENOSYS) ? ENOSYS : EIO;
47 return -1;
48 }
49 return 0;
50}
51} // namespace LIBC_NAMESPACE_DECL
52

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