Add new registers on Dalvik bytecode

Question

everyone. I met a problem on instrumentation on Dalvik bytecode.

The origin bytecode is:

virtual methods

.method public onClick(Landroid/view/View;)V

    .locals 12

    .param p1, "v"    # Landroid/view/View;

...

    return-void

.end method

To print something, I need to add 4 new registers. However, 12(local)+2(arguments)+4(new)>16 which will lead to problem for some instruction.

So, I think of a idea in blew way:

The number of whole registers are 20. v0-v11 are local, v18-v19 are arguments.

Move the v18-v19 to v12-v13 at first and arguments registers are within v15. In addition,

we need to modify p0 to v12, p1 to v13.

If we want to use 4 new registers, move v0-v3 to v14-17. After handling 4 new registers, move v14-v17 to v0-v3 back.

The new bytecode becomes:

virtual methods

.method public onClick(Landroid/view/View;)V

    .locals 18

    .param p1, "v"    # Landroid/view/View;

move v12, v18

move v13, v19

...

//want to use 4 new registers

move v14, v0

move v15, v1

move v16, v2

move v17, v3

//use 4 new registers

move v0, v14

move v1, v15

move v2, v16

move v3, v17

    return-void

.end method

Unfortunately, I met Java.lang.VerifyError. Could anyone help me? Thank you.

Answer 1

Registers are not interchangable. Some instructions accept only registers 0-15, others 0-255, so this approach wouldn't work.