Re: Locating where first param of an invoke gets put on the stack

Roberto,

Thank you!

I wrote a very huge solution to my problem. Hopped in the shower, and
thought of a 4 line solution. I'm just stuffing the params into locals,
inserting my log code, then dumping params back on the stack. Not pretty,
but works for my testing needs. It gets my code before the params.

I will check out defuse tomorrow, and reimplement if I ever need to take
this testing further.

Jon

On Fri, Dec 1, 2017 at 4:11 PM, Roberto Andrioli <[email protected]
> wrote:

> Hi Jon,
>
> You will need to implement a  simple symbolic interpreter to know this
> data flow information. I.e, that the definition of  `i` reaches the invoke
> of the method.
>
> I have implemented a simple tool that may help you with that. The tool is
> available here https://github.com/saeg/asm-defuse. I have no
> documentation (shame on me). I implemented it for data flow testing
> coverage, but I think that it may be useful for you needs.
>
> Best regards
>
> Roberto
>
> On Fri, Dec 1, 2017, 2:02 PM Jon Sawyer <[email protected]> wrote:
>
>> I want to thank everyone who worked on asm, such a wonderful framework. I
>> wish I had found it earlier, it would have saved me so much time. I have a
>> bad habit of reinventing the wheel when I need something, trying to avoid
>> that here if possible. Really hoping ASM contains some feature that could
>> make this easier.
>>
>> I'd like to inject some code prior to the first param of an invoke* is
>> put on the stack. My problem here is locating when the first param (or "sub
>> param" enters the stack);
>>
>> If it is something like
>>
>> Log.print("hello","world");
>> ---
>>  ldc           #29                 // String TAG
>>  ldc           #31                 // String MSG
>> 15: invokestatic  #37                 // Method
>> logg/loggl/Log.print:(Ljava/lang/String;Ljava/lang/String;)I
>>
>> it is fairly simple, I can just move back two positions and be in front
>> of the ldc "TAG", and then inject my code.
>>
>>
>> But when something like this happens it gets complicated , dosomething
>> takes 7 ints. I need to jump to right before the bipush 100, so I can't
>> simply move back 7 positions.
>>
>>  int i = 100;
>>  dosomething(x(32,i/2),1,20 * 2,1,1,81,1);
>> ---
>> bipush        100
>> istore_2
>> bipush        32
>> iload_2
>> iconst_2
>> idiv
>> invokestatic  #6                  // Method x:(II)I
>> iconst_1
>> bipush        40
>> iconst_1
>> iconst_1
>> bipush        81
>> iconst_1
>> invokestatic  #7                  // Method dosomething:(IIIIIII)Ljava/
>> lang/String;
>>
>> So, does ASM hold any magic for me here? Something easier than just
>> keeping track of the effects of each instruction on the stack, and walking
>> backwards?
>>
>> Thank You,
>> Jon
>>
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