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
14static unsigned long flag = PERF_FLAG_FD_CLOEXEC;
15
16int __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
29static 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
94unsigned 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