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