runtime/arch/x86/thread_x86.cc - platform/art - Git at Google

 /*
  * 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/macros.h"
 #include "thread-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;

   // Sanity check that reads from %fs point to this Thread*.
   Thread* self_check;
   CHECK_EQ(THREAD_SELF_OFFSET, SelfOffset<4>().Int32Value());
   __asm__ __volatile__("movl %%fs:(%1), %0"
       : "=r"(self_check)  // output
       : "r"(THREAD_SELF_OFFSET)  // input
       :);  // clobber
   CHECK_EQ(self_check, this);

   // Sanity check other offsets.
   CHECK_EQ(THREAD_EXCEPTION_OFFSET, ExceptionOffset<4>().Int32Value());
   CHECK_EQ(THREAD_CARD_TABLE_OFFSET, CardTableOffset<4>().Int32Value());
   CHECK_EQ(THREAD_ID_OFFSET, ThinLockIdOffset<4>().Int32Value());
 }

 void Thread::CleanupCpu() {
   MutexLock mu(this, *Locks::modify_ldt_lock_);

   // Sanity check that 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
	/*
	* 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/macros.h"
	#include "thread-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;

	// Sanity check that reads from %fs point to this Thread*.
	Thread* self_check;
	CHECK_EQ(THREAD_SELF_OFFSET, SelfOffset<4>().Int32Value());
	__asm__ __volatile__("movl %%fs:(%1), %0"
	: "=r"(self_check) // output
	: "r"(THREAD_SELF_OFFSET) // input
	:); // clobber
	CHECK_EQ(self_check, this);

	// Sanity check other offsets.
	CHECK_EQ(THREAD_EXCEPTION_OFFSET, ExceptionOffset<4>().Int32Value());
	CHECK_EQ(THREAD_CARD_TABLE_OFFSET, CardTableOffset<4>().Int32Value());
	CHECK_EQ(THREAD_ID_OFFSET, ThinLockIdOffset<4>().Int32Value());
	}

	void Thread::CleanupCpu() {
	MutexLock mu(this, *Locks::modify_ldt_lock_);

	// Sanity check that 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