1// SPDX-License-Identifier: GPL-2.0+
2/* This testcase operates with the test_fpu kernel driver.
3 * It modifies the FPU control register in user mode and calls the kernel
4 * module to perform floating point operations in the kernel. The control
5 * register value should be independent between kernel and user mode.
6 */
7
8#define _GNU_SOURCE
9#include <stdio.h>
10#include <errno.h>
11#include <string.h>
12#include <fenv.h>
13#include <unistd.h>
14#include <fcntl.h>
15
16const char *test_fpu_path = "/sys/kernel/debug/selftest_helpers/test_fpu";
17
18int main(void)
19{
20 char dummy[1];
21 int fd = open(test_fpu_path, O_RDONLY);
22
23 if (fd < 0) {
24 printf("[SKIP]\tcan't access %s: %s\n",
25 test_fpu_path, strerror(errno));
26 return 0;
27 }
28
29 if (read(fd, dummy, 1) < 0) {
30 printf("[FAIL]\taccess with default rounding mode failed\n");
31 return 1;
32 }
33
34 fesetround(FE_DOWNWARD);
35 if (read(fd, dummy, 1) < 0) {
36 printf("[FAIL]\taccess with downward rounding mode failed\n");
37 return 2;
38 }
39 if (fegetround() != FE_DOWNWARD) {
40 printf("[FAIL]\tusermode rounding mode clobbered\n");
41 return 3;
42 }
43
44 /* Note: the tests up to this point are quite safe and will only return
45 * an error. But the exception mask setting can cause misbehaving kernel
46 * to crash.
47 */
48 feclearexcept(FE_ALL_EXCEPT);
49 feenableexcept(FE_ALL_EXCEPT);
50 if (read(fd, dummy, 1) < 0) {
51 printf("[FAIL]\taccess with fpu exceptions unmasked failed\n");
52 return 4;
53 }
54 if (fegetexcept() != FE_ALL_EXCEPT) {
55 printf("[FAIL]\tusermode fpu exception mask clobbered\n");
56 return 5;
57 }
58
59 printf("[OK]\ttest_fpu\n");
60 return 0;
61}
62

source code of linux/tools/testing/selftests/fpu/test_fpu.c