73 lines
2.6 KiB
C++
73 lines
2.6 KiB
C++
/*
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* Copyright (C) 2008 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <limits.h>
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#include <pthread.h>
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#include <asm/ldt.h>
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extern "C" int __set_thread_area(user_desc*);
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__LIBC_HIDDEN__ void __init_user_desc(user_desc* result, bool allocate, void* base_addr) {
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if (allocate) {
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// Let the kernel choose.
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result->entry_number = -1;
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} else {
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// Get the existing entry number from %gs.
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uint32_t gs;
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__asm__ __volatile__("movw %%gs, %w0" : "=q"(gs) /*output*/);
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result->entry_number = (gs & 0xffff) >> 3;
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}
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result->base_addr = reinterpret_cast<uintptr_t>(base_addr);
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result->limit = 0xfffff;
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result->seg_32bit = 1;
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result->contents = MODIFY_LDT_CONTENTS_DATA;
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result->read_exec_only = 0;
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result->limit_in_pages = 1;
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result->seg_not_present = 0;
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result->useable = 1;
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}
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extern "C" __LIBC_HIDDEN__ int __set_tls(void* ptr) {
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user_desc tls_descriptor = {};
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__init_user_desc(&tls_descriptor, true, ptr);
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int rc = __set_thread_area(&tls_descriptor);
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if (rc != -1) {
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// Change %gs to be new GDT entry.
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uint16_t table_indicator = 0; // GDT
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uint16_t rpl = 3; // Requested privilege level
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uint16_t selector = (tls_descriptor.entry_number << 3) | table_indicator | rpl;
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__asm__ __volatile__("movw %w0, %%gs" : /*output*/ : "q"(selector) /*input*/ : /*clobber*/);
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}
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return rc;
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}
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