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
rdtsc(void)30 static uint64_t rdtsc(void)
31 {
32 uint32_t lo, hi;
33 /* We cannot use "=A", since this would use %rax on x86_64 */
34 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
35 return (uint64_t)hi << 32 | lo;
36 }
37
sigsegv_expect(int sig)38 static void sigsegv_expect(int sig)
39 {
40 /* */
41 }
42
segvtask(void)43 static 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
sigsegv_fail(int sig)58 static void sigsegv_fail(int sig)
59 {
60 fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
61 exit(0);
62 }
63
rdtsctask(void)64 static 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
main(void)77 int main(void)
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