tls.c

 1// SPDX-License-Identifier: GPL-2.0
 2#include <errno.h>
 3#include <linux/unistd.h>
 4
 5#include <sys/ptrace.h>
 6#include <sys/syscall.h>
 7#include <unistd.h>
 8
 9#include <os.h>
10#include <sysdep/tls.h>
11
12#ifndef PTRACE_GET_THREAD_AREA
13#define PTRACE_GET_THREAD_AREA 25
14#endif
15
16#ifndef PTRACE_SET_THREAD_AREA
17#define PTRACE_SET_THREAD_AREA 26
18#endif
19
20/* Checks whether host supports TLS, and sets *tls_min according to the value
21 * valid on the host.
22 * i386 host have it == 6; x86_64 host have it == 12, for i386 emulation. */
23void check_host_supports_tls(int *supports_tls, int *tls_min)
24{
25	/* Values for x86 and x86_64.*/
26	int val[] = {GDT_ENTRY_TLS_MIN_I386, GDT_ENTRY_TLS_MIN_X86_64};
27	int i;
28
29	for (i = 0; i < ARRAY_SIZE(val); i++) {
30		user_desc_t info;
31		info.entry_number = val[i];
32
33		if (syscall(__NR_get_thread_area, &info) == 0) {
34			*tls_min = val[i];
35			*supports_tls = 1;
36			return;
37		} else {
38			if (errno == EINVAL)
39				continue;
40			else if (errno == ENOSYS)
41				*supports_tls = 0;
42			return;
43		}
44	}
45
46	*supports_tls = 0;
47}
48
49int os_set_thread_area(user_desc_t *info, int pid)
50{
51	int ret;
52
53	ret = ptrace(PTRACE_SET_THREAD_AREA, pid, info->entry_number,
54		     (unsigned long) info);
55	if (ret < 0)
56		ret = -errno;
57	return ret;
58}
59
60int os_get_thread_area(user_desc_t *info, int pid)
61{
62	int ret;
63
64	ret = ptrace(PTRACE_GET_THREAD_AREA, pid, info->entry_number,
65		     (unsigned long) info);
66	if (ret < 0)
67		ret = -errno;
68	return ret;
69}