Re: Dalvik Interpreter mterp

[rachelqually]

Phehchcghhvtg
Fggrhh

[Rahul ramesh]

Hi,

Just looking in the code in /dalvik/vm/mterp/x86/entry.S for x86

I found that there are two macros at the end of function dvmMterpStdRun

FETCH_INST
GOTO_NEXT

All is see that FETCH_INST fetches the instruction to the register.

But its unclear as to who interprets the instruction from here onwards.

Can somebody point me to the files where code is interpreted.

I'm trying to understand the interpreter so it will be great if some one from the dalvik team can respond .

Regards,

Rahul R

[rasputin]

.macro GOTO_NEXT
215 movzx rINSTbl,%eax
216 movzbl rINSTbh,rINST
217 jmp *(rIBASE,%eax,4)
218.endm
at xref: /dalvik/vm/mterp/x86/header.S

On May 21, 5:02 pm, Rahul ramesh <rahulkalpsts...@gmail.com> wrote:
> Hi,
>

> Just looking in the code in /dalvik<http://androidxref.com/4.1.2/xref/dalvik/>
> /vm <http://androidxref.com/4.1.2/xref/dalvik/vm/>/mterp<http://androidxref.com/4.1.2/xref/dalvik/vm/mterp/>
> /x86 <http://androidxref.com/4.1.2/xref/dalvik/vm/mterp/x86/>/entry.S<http://androidxref.com/4.1.2/xref/dalvik/vm/mterp/x86/entry.S> for
> x86
> I found that there are two macros at the end of function dvmMterpStdRun<http://androidxref.com/4.1.2/s?refs=dvmMterpStdRun&project=dalvik>
>
> FETCH_INST <http://androidxref.com/4.1.2/s?defs=FETCH_INST&project=dalvik>GOTO_NEXT <http://androidxref.com/4.1.2/s?defs=GOTO_NEXT&project=dalvik>

[Kristopher Micinski]

The interpreter is written in such a way that it jumps from stub to
stub, so there's not really an interpretation "loop" per se. The next
instruction is interpreted by the code which handles the next
instruction:

http://androidxref.com/4.1.2/xref/dalvik/vm/mterp/x86/

See all of those OP_* files. Those handle the next instruction :-)

Kris

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[Kristopher Micinski]

Yes, that's a good point, the computation of which stub to go to is
computed: which can be done because all of the stubs fit within a set
space (you can jump if necessary).

Kris

[Rahul ramesh]

So rlBASE points to ?

Regards,

Rahul R

[Rahul ramesh]

Thank you for your reply.

So the dex files are optimized and put into shared memory .

And then who starts the parsing this memory and invoking the execution engine (The assembly code )

And and at what point are the offsets of instructions calculated ?

Regards,

Rahul R

[Kristopher Micinski]

Line 217 that you just posted jumps in a way such that the correct
instruction's stub is the target :-)

The instructions are organized into a jump table:

http://en.wikipedia.org/wiki/Branch_table

Again, the video I pointed to on Dalvik internals gives a pretty good
coverage of this from Dan Bornstein.

Kris

[Rahul ramesh]

Thanks Kristopher 

Regards,

Rahul R