卷二 Dalvik与Android源码分析 第五章 Interpreter与JIT 5.6 dalvik运行时帧结构 图书版试读--请勿转发

作者 crosskernel@gmail.com

在dalvik运行时每个函数也是有自己的Frame的，首先分析在dalvik源码里描述了对Frame结构的描述：

Low addresses (0x00000000)

+- - - - - - - - -+

- out0 -

+-----------------+ <-- stack ptr (top of stack)

+ VM-specific +

+ internal goop +

+-----------------+ <-- curFrame: FP for cur function

+ v0 == local0 +

+-----------------+ +-----------------+

+ out0 + + v1 == in0 +

+-----------------+ +-----------------+

+ out1 + + v2 == in1 +

+-----------------+ +-----------------+

+ VM-specific +

+ internal goop +

+-----------------+ <-- frame ptr (FP) for previous function

+ v0 == local0 +

+-----------------+

+ v1 == local1 +

+-----------------+

+ v2 == in0 +

+-----------------+

+ v3 == in1 +

+-----------------+

+ v4 == in2 +

+-----------------+

- -

- -

- -

+-----------------+ <-- interpStackStart

High addresses (0xffffffff)

其中寄存器分配规则是由dalvik编译器决定的。而VM-specific internal goop就是“struct StackSaveArea”，该结构定义如下：

struct StackSaveArea {

…

/* saved frame pointer for previous frame, or NULL if this is at bottom */

u4* prevFrame;

/* saved program counter (from method in caller's frame) */

//该PC指针为并不是二进制的r15，而是当前字节码地址

const u2* savedPc;

/* pointer to method we're *currently* executing; handy for exceptions */

const Method* method;

union {

/* for JNI native methods: bottom of local reference segment */

u4 localRefCookie;

/* for interpreted methods: saved current PC, for exception stack

* traces and debugger traces */

const u2* currentPc;

} xtra;

/* Native return pointer for JIT, or 0 if interpreted */

const u2* returnAddr;

…

};

“struct StackSaveArea”作用如下：

 保存当前字节码的地址到其成员变量“xtra. currentPc”

#define EXPORT_PC() \

str rPC, [rFP, #(-sizeofStackSaveArea + offStackSaveArea_currentPc)]

其中offStackSaveArea_currentPc被定义为12，sizeofStackSaveArea即为“struct StackSaveArea”结构的size。rFP为当前帧基地址，参考上一节的Frame结构，“[rFP, #(-sizeofStackSaveArea + offStackSaveArea_currentPc)]”为“xtra. currentPc”所在地址。