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  * when set with prctl()
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 
31 /* snippet from wikipedia :-) */
32 
33 static uint64_t rdtsc(void)
34 {
35 uint32_t lo, hi;
36 /* We cannot use "=A", since this would use %rax on x86_64 */
37 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
38 return (uint64_t)hi << 32 | lo;
39 }
40 
41 int should_segv = 0;
42 
43 static void sigsegv_cb(int sig)
44 {
45 	if (!should_segv)
46 	{
47 		fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
48 		exit(0);
49 	}
50 	if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
51 	{
52 		perror("prctl");
53 		exit(0);
54 	}
55 	should_segv = 0;
56 
57 	rdtsc();
58 }
59 
60 static void task(void)
61 {
62 	signal(SIGSEGV, sigsegv_cb);
63 	alarm(10);
64 	for(;;)
65 	{
66 		rdtsc();
67 		if (should_segv)
68 		{
69 			fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
70 			exit(0);
71 		}
72 		if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
73 		{
74 			perror("prctl");
75 			exit(0);
76 		}
77 		should_segv = 1;
78 	}
79 }
80 
81 
82 int main(void)
83 {
84 	int n_tasks = 100, i;
85 
86 	fprintf(stderr, "[No further output means we're allright]\n");
87 
88 	for (i=0; i<n_tasks; i++)
89 		if (fork() == 0)
90 			task();
91 
92 	for (i=0; i<n_tasks; i++)
93 		wait(NULL);
94 
95 	exit(0);
96 }
97 
98