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 
31 static uint64_t rdtsc(void)
32 {
33 uint32_t lo, hi;
34 /* We cannot use "=A", since this would use %rax on x86_64 */
35 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
36 return (uint64_t)hi << 32 | lo;
37 }
38 
39 static void sigsegv_expect(int sig)
40 {
41 	/* */
42 }
43 
44 static 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 
59 static void sigsegv_fail(int sig)
60 {
61 	fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
62 	exit(0);
63 }
64 
65 static 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 
78 int 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