[LLVMdev] Question About inserting Instruction?

[Qiuyu Zhang]

Hi, 

I am working on a project with LLVM. What I need to do is to generate/insert some dummy/dead basic blocls which never have chance to be executed and put some instructions in those dummy/dead basic blocks.

So far, the dummy/dead BB insertion is done. I am trying insert instructions in those dummy/dead BB. Actually, I can insert the legal instructions to dummy/dead BB, however, I really want to insert some illegal instructions/any thing into those BB since those instructions have no chance to be executed. I am not sure if it could be done or not. 

For example,
 Correct way:
    Instruction *NewInst = new LoadInst(...);
    NewBB->getInstList().push_back(NewInst);

 what I need just put some junk data in the BB, not instructions. From assemble code level, it looks like the following,

 a piece of code from correct instructions by disassemble object code.
   
:00000009 0533709283              add eax, 83927033
:0000000E 05A2B78135              add eax, 3581B7A2
:00000013 C1C819                  ror eax, 19
:00000016 05E5167711              add eax, 117716E5
:0000001B 0542F7A8DC              add eax, DCA8F742


:00000009 0533709283              add eax, 83927033
:0000000E 7878787878          ???                                    <<<<<<  here is the illegal instruction.
:00000013 23232                    ???                                    <<<<<<
:00000016 05E5167711              add eax, 117716E5
:0000001B 0542F7A8DC              add eax, DCA8F742

    what I tried is to make *NewInst point to random memory(cast to Instuction pointer) and push_back to instList. But I failed to do it. 
    
            Instruction *NewInst  =  ;   
            NewBB->getInstList().push_back(NewInst);

So I was wondering if it is allowed in LLVM or not, if so, how to do that?

Let me know if my question is not clear.

Thanks
Qiuyu



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