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 35 extern 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
