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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "thread.h"
#include <sys/syscall.h>
#include <sys/types.h>
#include "asm_support_x86.h"
#include "base/enums.h"
#include "base/macros.h"
#include "thread-current-inl.h"
#include "thread_list.h"
#if defined(__APPLE__)
#include <architecture/i386/table.h>
#include <i386/user_ldt.h>
struct descriptor_table_entry_t {
uint16_t limit0;
uint16_t base0;
unsigned base1: 8, type: 4, s: 1, dpl: 2, p: 1;
unsigned limit: 4, avl: 1, l: 1, d: 1, g: 1, base2: 8;
} __attribute__((packed));
#define MODIFY_LDT_CONTENTS_DATA 0
#else
#include <asm/ldt.h>
#endif
namespace art {
void Thread::InitCpu() {
// Take the ldt lock, Thread::Current isn't yet established.
MutexLock mu(nullptr, *Locks::modify_ldt_lock_);
const uintptr_t base = reinterpret_cast<uintptr_t>(this);
const size_t limit = sizeof(Thread);
const int contents = MODIFY_LDT_CONTENTS_DATA;
const int seg_32bit = 1;
const int read_exec_only = 0;
const int limit_in_pages = 1;
const int seg_not_present = 0;
const int useable = 1;
int entry_number;
uint16_t table_indicator;
#if defined(__APPLE__)
descriptor_table_entry_t entry;
memset(&entry, 0, sizeof(entry));
entry.limit0 = (limit & 0x0ffff);
entry.limit = (limit & 0xf0000) >> 16;
entry.base0 = (base & 0x0000ffff);
entry.base1 = (base & 0x00ff0000) >> 16;
entry.base2 = (base & 0xff000000) >> 24;
entry.type = ((read_exec_only ^ 1) << 1) | (contents << 2);
entry.s = 1;
entry.dpl = 0x3;
entry.p = seg_not_present ^ 1;
entry.avl = useable;
entry.l = 0;
entry.d = seg_32bit;
entry.g = limit_in_pages;
entry_number = i386_set_ldt(LDT_AUTO_ALLOC, reinterpret_cast<ldt_entry*>(&entry), 1);
if (entry_number == -1) {
PLOG(FATAL) << "i386_set_ldt failed";
}
table_indicator = 1 << 2; // LDT
#else
// We use a GDT entry on Linux.
user_desc gdt_entry;
memset(&gdt_entry, 0, sizeof(gdt_entry));
// On Linux, there are 3 TLS GDT entries. We use one of those to to store our segment descriptor
// data.
//
// This entry must be shared, as the kernel only guarantees three TLS entries. For simplicity
// (and locality), use this local global, which practically becomes readonly after the first
// (startup) thread of the runtime has been initialized (during Runtime::Start()).
//
// We also share this between all runtimes in the process. This is both for simplicity (one
// well-known slot) as well as to avoid the three-slot limitation. Downside is that we cannot
// free the slot when it is known that a runtime stops.
static unsigned int gdt_entry_number = -1;
if (gdt_entry_number == static_cast<unsigned int>(-1)) {
gdt_entry.entry_number = -1; // Let the kernel choose.
} else {
gdt_entry.entry_number = gdt_entry_number;
}
gdt_entry.base_addr = base;
gdt_entry.limit = limit;
gdt_entry.seg_32bit = seg_32bit;
gdt_entry.contents = contents;
gdt_entry.read_exec_only = read_exec_only;
gdt_entry.limit_in_pages = limit_in_pages;
gdt_entry.seg_not_present = seg_not_present;
gdt_entry.useable = useable;
int rc = syscall(__NR_set_thread_area, &gdt_entry);
if (rc != -1) {
entry_number = gdt_entry.entry_number;
if (gdt_entry_number == static_cast<unsigned int>(-1)) {
gdt_entry_number = entry_number; // Save the kernel-assigned entry number.
}
} else {
PLOG(FATAL) << "set_thread_area failed";
UNREACHABLE();
}
table_indicator = 0; // GDT
#endif
// Change %fs to be new DT entry.
uint16_t rpl = 3; // Requested privilege level
uint16_t selector = (entry_number << 3) | table_indicator | rpl;
__asm__ __volatile__("movw %w0, %%fs"
: // output
: "q"(selector) // input
:); // clobber
// Allow easy indirection back to Thread*.
tlsPtr_.self = this;
// Check that the reads from %fs point to this Thread*.
Thread* self_check;
CHECK_EQ(THREAD_SELF_OFFSET, SelfOffset<PointerSize::k32>().Int32Value());
__asm__ __volatile__("movl %%fs:(%1), %0"
: "=r"(self_check) // output
: "r"(THREAD_SELF_OFFSET) // input
:); // clobber
CHECK_EQ(self_check, this);
// Check the other offsets
CHECK_EQ(THREAD_EXCEPTION_OFFSET, ExceptionOffset<PointerSize::k32>().Int32Value());
CHECK_EQ(THREAD_CARD_TABLE_OFFSET, CardTableOffset<PointerSize::k32>().Int32Value());
CHECK_EQ(THREAD_ID_OFFSET, ThinLockIdOffset<PointerSize::k32>().Int32Value());
}
void Thread::CleanupCpu() {
MutexLock mu(this, *Locks::modify_ldt_lock_);
// Check that the reads from %fs point to this Thread*.
Thread* self_check;
__asm__ __volatile__("movl %%fs:(%1), %0"
: "=r"(self_check) // output
: "r"(THREAD_SELF_OFFSET) // input
:); // clobber
CHECK_EQ(self_check, this);
// Extract the LDT entry number from the FS register.
uint16_t selector;
__asm__ __volatile__("movw %%fs, %w0"
: "=q"(selector) // output
: // input
:); // clobber
// Free LDT entry.
#if defined(__APPLE__)
// TODO: release selectors on OS/X this is a leak which will cause ldt entries to be exhausted
// after enough threads are created. However, the following code results in kernel panics in OS/X
// 10.9.
UNUSED(selector);
// i386_set_ldt(selector >> 3, 0, 1);
#else
// Note if we wanted to clean up the GDT entry, we would do that here, when the *last* thread
// is being deleted. But see the comment on gdt_entry_number. Code would look like this:
//
// user_desc gdt_entry;
// memset(&gdt_entry, 0, sizeof(gdt_entry));
// gdt_entry.entry_number = selector >> 3;
// gdt_entry.contents = MODIFY_LDT_CONTENTS_DATA;
// // "Empty" = Delete = seg_not_present==1 && read_exec_only==1.
// gdt_entry.seg_not_present = 1;
// gdt_entry.read_exec_only = 1;
// syscall(__NR_set_thread_area, &gdt_entry);
UNUSED(selector);
#endif
}
} // namespace art
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