1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <limits.h>
30#include <pthread.h>
31#include <stdbool.h>
32
33#include <asm/ldt.h>
34
35extern int __set_thread_area(struct user_desc*);
36
37__LIBC_HIDDEN__ void __init_user_desc(struct user_desc* result, bool allocate, void* base_addr) {
38  if (allocate) {
39    // Let the kernel choose.
40    result->entry_number = -1;
41  } else {
42    // Get the existing entry number from %gs.
43    uint32_t gs;
44    __asm__ __volatile__("movw %%gs, %w0" : "=q"(gs) /*output*/);
45    result->entry_number = (gs & 0xffff) >> 3;
46  }
47
48  result->base_addr = (uintptr_t) base_addr;
49
50  result->limit = PAGE_SIZE;
51
52  result->seg_32bit = 1;
53  result->contents = MODIFY_LDT_CONTENTS_DATA;
54  result->read_exec_only = 0;
55  result->limit_in_pages = 1;
56  result->seg_not_present = 0;
57  result->useable = 1;
58}
59
60__LIBC_HIDDEN__ int __set_tls(void* ptr) {
61  struct user_desc tls_descriptor;
62  __init_user_desc(&tls_descriptor, true, ptr);
63
64  int rc = __set_thread_area(&tls_descriptor);
65  if (rc != -1) {
66    // Change %gs to be new GDT entry.
67    uint16_t table_indicator = 0;  // GDT
68    uint16_t rpl = 3;  // Requested privilege level
69    uint16_t selector = (tls_descriptor.entry_number << 3) | table_indicator | rpl;
70    __asm__ __volatile__("movw %w0, %%gs" : /*output*/ : "q"(selector) /*input*/ : /*clobber*/);
71  }
72
73  return rc;
74}
75