1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Tests for prctl(PR_GET_TSC, ...) / prctl(PR_SET_TSC, ...)
4 *
5 * Tests if the control register is updated correctly
6 * at context switches
7 *
8 * Warning: this test will cause a very high load for a few seconds
9 *
10 */
11
12#include <stdio.h>
13#include <stdlib.h>
14#include <unistd.h>
15#include <signal.h>
16#include <inttypes.h>
17#include <wait.h>
18
19
20#include <sys/prctl.h>
21#include <linux/prctl.h>
22
23/* Get/set the process' ability to use the timestamp counter instruction */
24#ifndef PR_GET_TSC
25#define PR_GET_TSC 25
26#define PR_SET_TSC 26
27# define PR_TSC_ENABLE		1   /* allow the use of the timestamp counter */
28# define PR_TSC_SIGSEGV		2   /* throw a SIGSEGV instead of reading the TSC */
29#endif
30
31static uint64_t rdtsc(void)
32{
33uint32_t lo, hi;
34/* We cannot use "=A", since this would use %rax on x86_64 */
35__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
36return (uint64_t)hi << 32 | lo;
37}
38
39static void sigsegv_expect(int sig)
40{
41	/* */
42}
43
44static void segvtask(void)
45{
46	if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
47	{
48		perror("prctl");
49		exit(0);
50	}
51	signal(SIGSEGV, sigsegv_expect);
52	alarm(10);
53	rdtsc();
54	fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
55	exit(0);
56}
57
58
59static void sigsegv_fail(int sig)
60{
61	fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
62	exit(0);
63}
64
65static void rdtsctask(void)
66{
67	if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
68	{
69		perror("prctl");
70		exit(0);
71	}
72	signal(SIGSEGV, sigsegv_fail);
73	alarm(10);
74	for(;;) rdtsc();
75}
76
77
78int main(void)
79{
80	int n_tasks = 100, i;
81
82	fprintf(stderr, "[No further output means we're all right]\n");
83
84	for (i=0; i<n_tasks; i++)
85		if (fork() == 0)
86		{
87			if (i & 1)
88				segvtask();
89			else
90				rdtsctask();
91		}
92
93	for (i=0; i<n_tasks; i++)
94		wait(NULL);
95
96	exit(0);
97}
98
99