彻底弄懂dalvik字节码【二】
彻底弄懂dalvik字节码【二】
用户2930595
发布于 2018-08-23 09:57:38
发布于 2018-08-23 09:57:38
【一】中讲到了最重要的dvmInterpret，继续跟：
void dvmInterpret(Thread* self, const Method* method, JValue* pResult)
{
InterpSaveState interpSaveState;
ExecutionSubModes savedSubModes;
#if defined(WITH_JIT)
/* Target-specific save/restore */
double calleeSave[JIT_CALLEE_SAVE_DOUBLE_COUNT];
/*
* If the previous VM left the code cache through single-stepping the
* inJitCodeCache flag will be set when the VM is re-entered (for example,
* in self-verification mode we single-step NEW_INSTANCE which may re-enter
* the VM through findClassFromLoaderNoInit). Because of that, we cannot
* assert that self->inJitCodeCache is NULL here.
*/
#endif
/*
* Save interpreter state from previous activation, linking
* new to last.
*/
interpSaveState = self->interpSave;
self->interpSave.prev = &interpSaveState;
/*
* Strip out and save any flags that should not be inherited by
* nested interpreter activation.
*/
savedSubModes = (ExecutionSubModes)(
self->interpBreak.ctl.subMode & LOCAL_SUBMODE);
if (savedSubModes != kSubModeNormal) {
dvmDisableSubMode(self, savedSubModes);
}
#if defined(WITH_JIT)
dvmJitCalleeSave(calleeSave);
#endif
#if defined(WITH_TRACKREF_CHECKS)
self->interpSave.debugTrackedRefStart =
dvmReferenceTableEntries(&self->internalLocalRefTable);
#endif
self->debugIsMethodEntry = true;
#if defined(WITH_JIT)
/* Initialize the state to kJitNot */
self->jitState = kJitNot;
#endif
/*
* Initialize working state.
*
* No need to initialize "retval".
*/
self->interpSave.method = method;
self->interpSave.curFrame = (u4*) self->interpSave.curFrame;
self->interpSave.pc = method->insns;
assert(!dvmIsNativeMethod(method));
/*
* Make sure the class is ready to go. Shouldn't be possible to get
* here otherwise.
*/
if (method->clazz->status < CLASS_INITIALIZING ||
method->clazz->status == CLASS_ERROR)
{
ALOGE("ERROR: tried to execute code in unprepared class '%s' (%d)",
method->clazz->descriptor, method->clazz->status);
dvmDumpThread(self, false);
dvmAbort();
}
typedef void (*Interpreter)(Thread*);
Interpreter stdInterp;
if (gDvm.executionMode == kExecutionModeInterpFast)
stdInterp = dvmMterpStd;
#if defined(WITH_JIT)
else if (gDvm.executionMode == kExecutionModeJit ||
gDvm.executionMode == kExecutionModeNcgO0 ||
gDvm.executionMode == kExecutionModeNcgO1)
stdInterp = dvmMterpStd;
#endif
else
stdInterp = dvmInterpretPortable;
// Call the interpreter
(*stdInterp)(self);
*pResult = self->interpSave.retval;
/* Restore interpreter state from previous activation */
self->interpSave = interpSaveState;
#if defined(WITH_JIT)
dvmJitCalleeRestore(calleeSave);
#endif
if (savedSubModes != kSubModeNormal) {
dvmEnableSubMode(self, savedSubModes);
}
}这个方法中先保存了前一个方法的状态，然后初始化当前方法的状态，比如设置pc指向方法的字节码开始处等。然后调用dvmInterpretPortable开始解释执行，执行完毕后，恢复了前一个方法的状态。
继续跟dvmInterpretPortable:
void dvmInterpretPortable(Thread* self)
{
#if defined(EASY_GDB)
StackSaveArea* debugSaveArea = SAVEAREA_FROM_FP(self->interpSave.curFrame);
#endif
DvmDex* methodClassDex; // curMethod->clazz->pDvmDex
JValue retval;
/* core state */
const Method* curMethod; // method we're interpreting
const u2* pc; // program counter
u4* fp; // frame pointer
u2 inst; // current instruction
/* instruction decoding */
u4 ref; // 16 or 32-bit quantity fetched directly
u2 vsrc1, vsrc2, vdst; // usually used for register indexes
/* method call setup */
const Method* methodToCall;
bool methodCallRange;
/* static computed goto table */
DEFINE_GOTO_TABLE(handlerTable);
/* copy state in */
curMethod = self->interpSave.method;
pc = self->interpSave.pc;
fp = self->interpSave.curFrame;
retval = self->interpSave.retval; /* only need for kInterpEntryReturn? */
methodClassDex = curMethod->clazz->pDvmDex;
LOGVV("threadid=%d: %s.%s pc=%#x fp=%p",
self->threadId, curMethod->clazz->descriptor, curMethod->name,
pc - curMethod->insns, fp);
/*
* Handle any ongoing profiling and prep for debugging.
*/
if (self->interpBreak.ctl.subMode != 0) {
TRACE_METHOD_ENTER(self, curMethod);
self->debugIsMethodEntry = true; // Always true on startup
}
/*
* DEBUG: scramble this to ensure we're not relying on it.
*/
methodToCall = (const Method*) -1;
#if 0
if (self->debugIsMethodEntry) {
ILOGD("|-- Now interpreting %s.%s", curMethod->clazz->descriptor,
curMethod->name);
DUMP_REGS(curMethod, self->interpSave.curFrame, false);
}
#endif
FINISH(0); /* fetch and execute first instruction */
/*--- start of opcodes ---*/细心的朋友在阅读源码的时候，可能会发现这个方法的方法体括号居然没有闭合，这是有原因的，因为这里面有很多的宏定义，宏定义展开后，才是完整的方法体。
我们可以看到，这个方法中，直接从之前分配的栈帧中获取各类信息，比如当前执行的method等，同时申明了若干变量：pc、fp、inst等，这些变量在后面分析的宏中被直接赋值和使用，所以在后面分析宏的时候，留意这些变量。
第一个宏DEFINE_GOTO_TABLE:
#define DEFINE_GOTO_TABLE(_name) \
static const void* _name[kNumPackedOpcodes] = { \
/* BEGIN(libdex-goto-table); GENERATED AUTOMATICALLY BY opcode-gen */ \
H(OP_NOP), \
H(OP_MOVE), \
H(OP_MOVE_FROM16), \
H(OP_MOVE_16), \
H(OP_MOVE_WIDE), \
H(OP_MOVE_WIDE_FROM16), \
H(OP_MOVE_WIDE_16), \
H(OP_MOVE_OBJECT), \
H(OP_MOVE_OBJECT_FROM16), \
H(OP_MOVE_OBJECT_16), \
H(OP_MOVE_RESULT), \
H(OP_MOVE_RESULT_WIDE), \
H(OP_MOVE_RESULT_OBJECT), \
H(OP_MOVE_EXCEPTION), \
H(OP_RETURN_VOID), \
H(OP_RETURN), \
H(OP_RETURN_WIDE), \
H(OP_RETURN_OBJECT), \
H(OP_CONST_4), \
H(OP_CONST_16), \
H(OP_CONST), \
H(OP_CONST_HIGH16), \
H(OP_CONST_WIDE_16), \
H(OP_CONST_WIDE_32), \
H(OP_CONST_WIDE), \
H(OP_CONST_WIDE_HIGH16), \
H(OP_CONST_STRING), \
H(OP_CONST_STRING_JUMBO), \
H(OP_CONST_CLASS), \
H(OP_MONITOR_ENTER), \
H(OP_MONITOR_EXIT), \
H(OP_CHECK_CAST), \
H(OP_INSTANCE_OF), \
H(OP_ARRAY_LENGTH), \
H(OP_NEW_INSTANCE), \
H(OP_NEW_ARRAY), \
H(OP_FILLED_NEW_ARRAY), \
H(OP_FILLED_NEW_ARRAY_RANGE), \
H(OP_FILL_ARRAY_DATA), \
H(OP_THROW), \
H(OP_GOTO), \
H(OP_GOTO_16), \
H(OP_GOTO_32), \
H(OP_PACKED_SWITCH), \
H(OP_SPARSE_SWITCH), \
H(OP_CMPL_FLOAT), \
H(OP_CMPG_FLOAT), \
H(OP_CMPL_DOUBLE), \
H(OP_CMPG_DOUBLE), \
H(OP_CMP_LONG), \
H(OP_IF_EQ), \
H(OP_IF_NE), \
H(OP_IF_LT), \
H(OP_IF_GE), \
H(OP_IF_GT), \
H(OP_IF_LE), \
H(OP_IF_EQZ), \
H(OP_IF_NEZ), \
H(OP_IF_LTZ), \
H(OP_IF_GEZ), \
H(OP_IF_GTZ), \
H(OP_IF_LEZ), \
H(OP_UNUSED_3E), \
H(OP_UNUSED_3F), \
H(OP_UNUSED_40), \
H(OP_UNUSED_41), \
H(OP_UNUSED_42), \
H(OP_UNUSED_43), \
H(OP_AGET), \
H(OP_AGET_WIDE), \
H(OP_AGET_OBJECT), \
H(OP_AGET_BOOLEAN), \
H(OP_AGET_BYTE), \
H(OP_AGET_CHAR), \
H(OP_AGET_SHORT), \
H(OP_APUT), \
H(OP_APUT_WIDE), \
H(OP_APUT_OBJECT), \
H(OP_APUT_BOOLEAN), \
H(OP_APUT_BYTE), \
H(OP_APUT_CHAR), \
H(OP_APUT_SHORT), \
H(OP_IGET), \
H(OP_IGET_WIDE), \
H(OP_IGET_OBJECT), \
H(OP_IGET_BOOLEAN), \
H(OP_IGET_BYTE), \
H(OP_IGET_CHAR), \
H(OP_IGET_SHORT), \
H(OP_IPUT), \
H(OP_IPUT_WIDE), \
H(OP_IPUT_OBJECT), \
H(OP_IPUT_BOOLEAN), \
H(OP_IPUT_BYTE), \
H(OP_IPUT_CHAR), \
H(OP_IPUT_SHORT), \
H(OP_SGET), \
H(OP_SGET_WIDE), \
H(OP_SGET_OBJECT), \
H(OP_SGET_BOOLEAN), \
H(OP_SGET_BYTE), \
H(OP_SGET_CHAR), \
H(OP_SGET_SHORT), \
H(OP_SPUT), \
H(OP_SPUT_WIDE), \
H(OP_SPUT_OBJECT), \
H(OP_SPUT_BOOLEAN), \
H(OP_SPUT_BYTE), \
H(OP_SPUT_CHAR), \
H(OP_SPUT_SHORT), \
H(OP_INVOKE_VIRTUAL), \
H(OP_INVOKE_SUPER), \
H(OP_INVOKE_DIRECT), \
H(OP_INVOKE_STATIC), \
H(OP_INVOKE_INTERFACE), \
H(OP_UNUSED_73), \
H(OP_INVOKE_VIRTUAL_RANGE), \
H(OP_INVOKE_SUPER_RANGE), \
H(OP_INVOKE_DIRECT_RANGE), \
H(OP_INVOKE_STATIC_RANGE), \
H(OP_INVOKE_INTERFACE_RANGE), \
H(OP_UNUSED_79), \
H(OP_UNUSED_7A), \
H(OP_NEG_INT), \
H(OP_NOT_INT), \
H(OP_NEG_LONG), \
H(OP_NOT_LONG), \
H(OP_NEG_FLOAT), \
H(OP_NEG_DOUBLE), \
H(OP_INT_TO_LONG), \
H(OP_INT_TO_FLOAT), \
H(OP_INT_TO_DOUBLE), \
H(OP_LONG_TO_INT), \
H(OP_LONG_TO_FLOAT), \
H(OP_LONG_TO_DOUBLE), \
H(OP_FLOAT_TO_INT), \
H(OP_FLOAT_TO_LONG), \
H(OP_FLOAT_TO_DOUBLE), \
H(OP_DOUBLE_TO_INT), \
H(OP_DOUBLE_TO_LONG), \
H(OP_DOUBLE_TO_FLOAT), \
H(OP_INT_TO_BYTE), \
H(OP_INT_TO_CHAR), \
H(OP_INT_TO_SHORT), \
H(OP_ADD_INT), \
H(OP_SUB_INT), \
H(OP_MUL_INT), \
H(OP_DIV_INT), \
H(OP_REM_INT), \
H(OP_AND_INT), \
H(OP_OR_INT), \
H(OP_XOR_INT), \
H(OP_SHL_INT), \
H(OP_SHR_INT), \
H(OP_USHR_INT), \
H(OP_ADD_LONG), \
H(OP_SUB_LONG), \
H(OP_MUL_LONG), \
H(OP_DIV_LONG), \
H(OP_REM_LONG), \
H(OP_AND_LONG), \
H(OP_OR_LONG), \
H(OP_XOR_LONG), \
H(OP_SHL_LONG), \
H(OP_SHR_LONG), \
H(OP_USHR_LONG), \
H(OP_ADD_FLOAT), \
H(OP_SUB_FLOAT), \
H(OP_MUL_FLOAT), \
H(OP_DIV_FLOAT), \
H(OP_REM_FLOAT), \
H(OP_ADD_DOUBLE), \
H(OP_SUB_DOUBLE), \
H(OP_MUL_DOUBLE), \
H(OP_DIV_DOUBLE), \
H(OP_REM_DOUBLE), \
H(OP_ADD_INT_2ADDR), \
H(OP_SUB_INT_2ADDR), \
H(OP_MUL_INT_2ADDR), \
H(OP_DIV_INT_2ADDR), \
H(OP_REM_INT_2ADDR), \
H(OP_AND_INT_2ADDR), \
H(OP_OR_INT_2ADDR), \
H(OP_XOR_INT_2ADDR), \
H(OP_SHL_INT_2ADDR), \
H(OP_SHR_INT_2ADDR), \
H(OP_USHR_INT_2ADDR), \
H(OP_ADD_LONG_2ADDR), \
H(OP_SUB_LONG_2ADDR), \
H(OP_MUL_LONG_2ADDR), \
H(OP_DIV_LONG_2ADDR), \
H(OP_REM_LONG_2ADDR), \
H(OP_AND_LONG_2ADDR), \
H(OP_OR_LONG_2ADDR), \
H(OP_XOR_LONG_2ADDR), \
H(OP_SHL_LONG_2ADDR), \
H(OP_SHR_LONG_2ADDR), \
H(OP_USHR_LONG_2ADDR), \
H(OP_ADD_FLOAT_2ADDR), \
H(OP_SUB_FLOAT_2ADDR), \
H(OP_MUL_FLOAT_2ADDR), \
H(OP_DIV_FLOAT_2ADDR), \
H(OP_REM_FLOAT_2ADDR), \
H(OP_ADD_DOUBLE_2ADDR), \
H(OP_SUB_DOUBLE_2ADDR), \
H(OP_MUL_DOUBLE_2ADDR), \
H(OP_DIV_DOUBLE_2ADDR), \
H(OP_REM_DOUBLE_2ADDR), \
H(OP_ADD_INT_LIT16), \
H(OP_RSUB_INT), \
H(OP_MUL_INT_LIT16), \
H(OP_DIV_INT_LIT16), \
H(OP_REM_INT_LIT16), \
H(OP_AND_INT_LIT16), \
H(OP_OR_INT_LIT16), \
H(OP_XOR_INT_LIT16), \
H(OP_ADD_INT_LIT8), \
H(OP_RSUB_INT_LIT8), \
H(OP_MUL_INT_LIT8), \
H(OP_DIV_INT_LIT8), \
H(OP_REM_INT_LIT8), \
H(OP_AND_INT_LIT8), \
H(OP_OR_INT_LIT8), \
H(OP_XOR_INT_LIT8), \
H(OP_SHL_INT_LIT8), \
H(OP_SHR_INT_LIT8), \
H(OP_USHR_INT_LIT8), \
H(OP_IGET_VOLATILE), \
H(OP_IPUT_VOLATILE), \
H(OP_SGET_VOLATILE), \
H(OP_SPUT_VOLATILE), \
H(OP_IGET_OBJECT_VOLATILE), \
H(OP_IGET_WIDE_VOLATILE), \
H(OP_IPUT_WIDE_VOLATILE), \
H(OP_SGET_WIDE_VOLATILE), \
H(OP_SPUT_WIDE_VOLATILE), \
H(OP_BREAKPOINT), \
H(OP_THROW_VERIFICATION_ERROR), \
H(OP_EXECUTE_INLINE), \
H(OP_EXECUTE_INLINE_RANGE), \
H(OP_INVOKE_OBJECT_INIT_RANGE), \
H(OP_RETURN_VOID_BARRIER), \
H(OP_IGET_QUICK), \
H(OP_IGET_WIDE_QUICK), \
H(OP_IGET_OBJECT_QUICK), \
H(OP_IPUT_QUICK), \
H(OP_IPUT_WIDE_QUICK), \
H(OP_IPUT_OBJECT_QUICK), \
H(OP_INVOKE_VIRTUAL_QUICK), \
H(OP_INVOKE_VIRTUAL_QUICK_RANGE), \
H(OP_INVOKE_SUPER_QUICK), \
H(OP_INVOKE_SUPER_QUICK_RANGE), \
H(OP_IPUT_OBJECT_VOLATILE), \
H(OP_SGET_OBJECT_VOLATILE), \
H(OP_SPUT_OBJECT_VOLATILE), \
H(OP_UNUSED_FF), \
/* END(libdex-goto-table) */ \
};这个宏展开了就是定义了一个指针数组handlerTable，共256项，每一项对应dalvik的一个操作码。
这个指针数组是在dvmInterpretPortable被展开的，也就是说是局部变量，指令的跳转，就是在这张表中跳转，与传统的方法调用相比，省去了方法调用的栈构造，执行效率得到提升。但是这对编码的要求就很高，其中用到大量的宏就可以看出他们的深厚功底。
继续分析宏H:
# define H(_op) &&op_##_op其中&&表示间接引用，##表示字符串拼接。比如说H(OP_NOP)展开就是：&&op_OP_NOP，也就是对op_OP_NOP的间接引用（指针）。
而op_OP_NOP又是通过另外一个宏HANDLE_OPCODE来定义的：
# define HANDLE_OPCODE(_op) op_##_op:. HANDLE_OPCODE(OP_NOP)展开就是：op_OP_NOP:。
注意最后的冒号，这表示它其实是一个位置标签。
所以handlerTable就是若干地址标签的引用数组。
回到dvmInterpretPortable，继续分析宏FINISH：
# define FINISH(_offset) { \
ADJUST_PC(_offset); \
inst = FETCH(0); \
if (self->interpBreak.ctl.subMode) { \
dvmCheckBefore(pc, fp, self); \
} \
goto *handlerTable[INST_INST(inst)]; \
}
# define FINISH_BKPT(_opcode) { \
goto *handlerTable[_opcode]; \
}
#define OP_END其中的宏ADJUST_PC:
#ifdef CHECK_BRANCH_OFFSETS
# define ADJUST_PC(_offset) do { \
int myoff = _offset; /* deref only once */ \
if (pc + myoff < curMethod->insns || \
pc + myoff >= curMethod->insns + dvmGetMethodInsnsSize(curMethod)) \
{ \
char* desc; \
desc = dexProtoCopyMethodDescriptor(&curMethod->prototype); \
ALOGE("Invalid branch %d at 0x%04x in %s.%s %s", \
myoff, (int) (pc - curMethod->insns), \
curMethod->clazz->descriptor, curMethod->name, desc); \
free(desc); \
dvmAbort(); \
} \
pc += myoff; \
EXPORT_EXTRA_PC(); \
} while (false)
#else
# define ADJUST_PC(_offset) do { \
pc += _offset; \
EXPORT_EXTRA_PC(); \
} while (false)
#endif其实就是将pc调整_offset个偏移量。
接下来就是宏FETCH:
#define FETCH(_offset) (pc[(_offset)])inst = FETCH(0);就是从pc的0偏移处开始取指令（两个字节，前面的申明： u2 inst）存放到inst中。
然后通过宏INST_INST，得到该指令在handlerTable中的索引：
#define INST_INST(_inst) ((_inst) & 0xff)也就是说是低字节是操作码的索引号。当获取到索引号之后，就通过handlerTable跳转到对应的代码处开始执行。
前面我们知道，通过宏HANDLE_OPCODE对标签进行定义，在dalvik/vm/mterp/c目录下，对每一个操作码都有个文件，里面对应就是其HANDLE_OPCODE标签的定义，也就是其实现细节：
我们以OP_NOP为例分析一下：
HANDLE_OPCODE(OP_NOP)
FINISH(1);
OP_END其逻辑就是啥也没干，继续读取下一条指令FINISH(1)执行。
ok，先到这里，下一篇以一个实际的例子来说明具体的解析过程。
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原始发表：2016.10.23 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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