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
 20static char auxv[4096];
 21
 22int read_auxv(char *buf, ssize_t buf_size)
 23{
 24	ssize_t num;
 25	int rc, fd;
 26
 27	fd = open("/proc/self/auxv", O_RDONLY);
 28	if (fd == -1) {
 29		perror("open");
 30		return -errno;
 31	}
 32
 33	num = read(fd, buf, buf_size);
 34	if (num < 0) {
 35		perror("read");
 36		rc = -EIO;
 37		goto out;
 38	}
 39
 40	if (num > buf_size) {
 41		printf("overflowed auxv buffer\n");
 42		rc = -EOVERFLOW;
 43		goto out;
 44	}
 45
 46	rc = 0;
 47out:
 48	close(fd);
 49	return rc;
 50}
 51
 52void *find_auxv_entry(int type, char *auxv)
 53{
 54	ElfW(auxv_t) *p;
 55
 56	p = (ElfW(auxv_t) *)auxv;
 57
 58	while (p->a_type != AT_NULL) {
 59		if (p->a_type == type)
 60			return p;
 61
 62		p++;
 63	}
 64
 65	return NULL;
 66}
 67
 68void *get_auxv_entry(int type)
 69{
 70	ElfW(auxv_t) *p;
 71
 72	if (read_auxv(auxv, sizeof(auxv)))
 73		return NULL;
 74
 75	p = find_auxv_entry(type, auxv);
 76	if (p)
 77		return (void *)p->a_un.a_val;
 78
 79	return NULL;
 80}
 81
 82int pick_online_cpu(void)
 83{
 84	cpu_set_t mask;
 85	int cpu;
 86
 87	CPU_ZERO(&mask);
 88
 89	if (sched_getaffinity(0, sizeof(mask), &mask)) {
 90		perror("sched_getaffinity");
 91		return -1;
 92	}
 93
 94	/* We prefer a primary thread, but skip 0 */
 95	for (cpu = 8; cpu < CPU_SETSIZE; cpu += 8)
 96		if (CPU_ISSET(cpu, &mask))
 97			return cpu;
 98
 99	/* Search for anything, but in reverse */
100	for (cpu = CPU_SETSIZE - 1; cpu >= 0; cpu--)
101		if (CPU_ISSET(cpu, &mask))
102			return cpu;
103
104	printf("No cpus in affinity mask?!\n");
105	return -1;
106}