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
16 static int perf_flag_probe(void)
17 {
18 /* use 'safest' configuration as used in evsel__fallback() */
19 struct perf_event_attr attr = {
20 .type = PERF_TYPE_SOFTWARE,
21 .config = PERF_COUNT_SW_CPU_CLOCK,
22 .exclude_kernel = 1,
23 };
24 int fd;
25 int err;
26 int cpu;
27 pid_t pid = -1;
28 char sbuf[STRERR_BUFSIZE];
29
30 cpu = sched_getcpu();
31 if (cpu < 0)
32 cpu = 0;
33
34 /*
35 * Using -1 for the pid is a workaround to avoid gratuitous jump label
36 * changes.
37 */
38 while (1) {
39 /* check cloexec flag */
40 fd = sys_perf_event_open(&attr, pid, cpu, -1,
41 PERF_FLAG_FD_CLOEXEC);
42 if (fd < 0 && pid == -1 && errno == EACCES) {
43 pid = 0;
44 continue;
45 }
46 break;
47 }
48 err = errno;
49
50 if (fd >= 0) {
51 close(fd);
52 return 1;
53 }
54
55 WARN_ONCE(err != EINVAL && err != EBUSY && err != EACCES,
56 "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
57 err, str_error_r(err, sbuf, sizeof(sbuf)));
58
59 /* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
60 while (1) {
61 fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
62 if (fd < 0 && pid == -1 && errno == EACCES) {
63 pid = 0;
64 continue;
65 }
66 break;
67 }
68 err = errno;
69
70 if (fd >= 0)
71 close(fd);
72
73 if (WARN_ONCE(fd < 0 && err != EBUSY && err != EACCES,
74 "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
75 err, str_error_r(err, sbuf, sizeof(sbuf))))
76 return -1;
77
78 return 0;
79 }
80
81 unsigned long perf_event_open_cloexec_flag(void)
82 {
83 static bool probed;
84
85 if (!probed) {
86 if (perf_flag_probe() <= 0)
87 flag = 0;
88 probed = true;
89 }
90
91 return flag;
92 }
93
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