1 /*
2  * Copyright 2013-2015, Michael Ellerman, IBM Corp.
3  * Licensed under GPLv2.
4  */
5 
6 #define _GNU_SOURCE	/* For CPU_ZERO etc. */
7 
8 #include <elf.h>
9 #include <errno.h>
10 #include <fcntl.h>
11 #include <link.h>
12 #include <sched.h>
13 #include <stdio.h>
14 #include <sys/stat.h>
15 #include <sys/types.h>
16 #include <unistd.h>
17 
18 #include "utils.h"
19 
20 static char auxv[4096];
21 
22 void *get_auxv_entry(int type)
23 {
24 	ElfW(auxv_t) *p;
25 	void *result;
26 	ssize_t num;
27 	int fd;
28 
29 	fd = open("/proc/self/auxv", O_RDONLY);
30 	if (fd == -1) {
31 		perror("open");
32 		return NULL;
33 	}
34 
35 	result = NULL;
36 
37 	num = read(fd, auxv, sizeof(auxv));
38 	if (num < 0) {
39 		perror("read");
40 		goto out;
41 	}
42 
43 	if (num > sizeof(auxv)) {
44 		printf("Overflowed auxv buffer\n");
45 		goto out;
46 	}
47 
48 	p = (ElfW(auxv_t) *)auxv;
49 
50 	while (p->a_type != AT_NULL) {
51 		if (p->a_type == type) {
52 			result = (void *)p->a_un.a_val;
53 			break;
54 		}
55 
56 		p++;
57 	}
58 out:
59 	close(fd);
60 	return result;
61 }
62 
63 int pick_online_cpu(void)
64 {
65 	cpu_set_t mask;
66 	int cpu;
67 
68 	CPU_ZERO(&mask);
69 
70 	if (sched_getaffinity(0, sizeof(mask), &mask)) {
71 		perror("sched_getaffinity");
72 		return -1;
73 	}
74 
75 	/* We prefer a primary thread, but skip 0 */
76 	for (cpu = 8; cpu < CPU_SETSIZE; cpu += 8)
77 		if (CPU_ISSET(cpu, &mask))
78 			return cpu;
79 
80 	/* Search for anything, but in reverse */
81 	for (cpu = CPU_SETSIZE - 1; cpu >= 0; cpu--)
82 		if (CPU_ISSET(cpu, &mask))
83 			return cpu;
84 
85 	printf("No cpus in affinity mask?!\n");
86 	return -1;
87 }
88