1 // SPDX-License-Identifier: GPL-2.0
2 #include <errno.h>
3 #include <sched.h>
4 #include "util.h" // for sched_getcpu()
5 #include "../perf-sys.h"
6 #include "cloexec.h"
7 #include "event.h"
8 #include "asm/bug.h"
9 #include "debug.h"
10 #include <unistd.h>
11 #include <sys/syscall.h>
12 #include <linux/string.h>
13
14 static unsigned long flag = PERF_FLAG_FD_CLOEXEC;
15
sched_getcpu(void)16 int __weak sched_getcpu(void)
17 {
18 #ifdef __NR_getcpu
19 unsigned cpu;
20 int err = syscall(__NR_getcpu, &cpu, NULL, NULL);
21 if (!err)
22 return cpu;
23 #else
24 errno = ENOSYS;
25 #endif
26 return -1;
27 }
28
perf_flag_probe(void)29 static int perf_flag_probe(void)
30 {
31 /* use 'safest' configuration as used in evsel__fallback() */
32 struct perf_event_attr attr = {
33 .type = PERF_TYPE_SOFTWARE,
34 .config = PERF_COUNT_SW_CPU_CLOCK,
35 .exclude_kernel = 1,
36 };
37 int fd;
38 int err;
39 int cpu;
40 pid_t pid = -1;
41 char sbuf[STRERR_BUFSIZE];
42
43 cpu = sched_getcpu();
44 if (cpu < 0)
45 cpu = 0;
46
47 /*
48 * Using -1 for the pid is a workaround to avoid gratuitous jump label
49 * changes.
50 */
51 while (1) {
52 /* check cloexec flag */
53 fd = sys_perf_event_open(&attr, pid, cpu, -1,
54 PERF_FLAG_FD_CLOEXEC);
55 if (fd < 0 && pid == -1 && errno == EACCES) {
56 pid = 0;
57 continue;
58 }
59 break;
60 }
61 err = errno;
62
63 if (fd >= 0) {
64 close(fd);
65 return 1;
66 }
67
68 WARN_ONCE(err != EINVAL && err != EBUSY && err != EACCES,
69 "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
70 err, str_error_r(err, sbuf, sizeof(sbuf)));
71
72 /* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
73 while (1) {
74 fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
75 if (fd < 0 && pid == -1 && errno == EACCES) {
76 pid = 0;
77 continue;
78 }
79 break;
80 }
81 err = errno;
82
83 if (fd >= 0)
84 close(fd);
85
86 if (WARN_ONCE(fd < 0 && err != EBUSY && err != EACCES,
87 "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
88 err, str_error_r(err, sbuf, sizeof(sbuf))))
89 return -1;
90
91 return 0;
92 }
93
perf_event_open_cloexec_flag(void)94 unsigned long perf_event_open_cloexec_flag(void)
95 {
96 static bool probed;
97
98 if (!probed) {
99 if (perf_flag_probe() <= 0)
100 flag = 0;
101 probed = true;
102 }
103
104 return flag;
105 }
106