Re: how to set some value at a memory location in stack

[Vaibhav Shrimali <vaibhav dot shrimali at gmail dot com>]

Well,
now I have stored the memory location, where I need to insert my
value, in the EDX register. I am not using force_reg() now.
I have stored the value to be inserted in a rtx type register.
But how do I set the value of memory location in EDX with the value
stored in a rtx type register?
Is there any library function which will allow me to do so?

Here is my code:

  if (frame_pointer_needed)
    { rtx r, set1,m1,edx,insn,temp;
      //Here hard frame pointer is pushed onto the stack
      insn = emit_insn (gen_push (hard_frame_pointer_rtx));
      RTX_FRAME_RELATED_P (insn) = 1;
      //Here hard frame pointer is updated
      insn = emit_move_insn (hard_frame_pointer_rtx, stack_pointer_rtx);
      RTX_FRAME_RELATED_P (insn) = 1;

      //my code starts from here.
      r = cfun->machine->force_align_arg_pointer;
      r = gen_rtx_PLUS (Pmode, r, -8);
      r = gen_rtx_MEM (Pmode, r);
      edx = gen_rtx_REG (Pmode, DX_REG);
      emit_move_insn(edx,r);
      //EDX now contains the memory location

      //Here I have stored the return address pushed on the stack in ret_addr
      //So the following code generates a rtx variable
      //which has the value ret_addr XOR hard_frame_pointer

      m1 = simplify_binary_operation(XOR, Pmode, ret_addr,
hard_frame_pointer_rtx);
     //now how to set memory location in edx with value m1??? Is there
any function
     //to do so.If not, please suggest me some other way of doing so.

    }

On Wed, Apr 14, 2010 at 7:44 PM, Ian Lance Taylor <iant@google.com> wrote:
> Vaibhav Shrimali <vaibhav.shrimali@gmail.com> writes:
>
>> I can use a hard register for this task. But will it allow me to
>> modify the memory location, between original return address and saved
>> frame pointer, stored in it?
>
> My point about the hard register was that you can't call force_reg
> after register allocation.
>
>> I think it will be just saved in the "saved registers" area of stack.
>> The assembly conversion of the prologue I need is:
>>
>> POP EAX ? ? ? ? ? ? ? ? ? ? ? ; new prologue start
>> PUSH EAX ? ? ? ? ? ? ?; unencrypted return address
>> PUSH EAX ? ? ? ? ? ? ?; duplicate return address
>> PUSH EBP ? ? ? ? ? ? ?; standard prologue
>> MOVE EBP, ESP
>> XOR [EBP+4], EBP ? ? ?; [EBP+4] has EIP and XOR encryptes ret addr(EIP)
>>
>> I want to know the function which allows me to write a value at a
>> memory address specified by a variable (generated by gen_rtx_MEM).
>> I thought force_reg is the one. Now, can I use ebx/ecx/...etc register
>> for the purpose.
>> OR will copy_to_mode_reg() function do the job?
>> OR is there any other function to do the job?
>
> You need to copy your memory location into a register. ?force_reg
> copies it into a pseudo-register. ?You need to copy it into a chosen
> hard register. ?Use emit_move_insn.
>
> Ian
>



-- 
Vaibhav Shrimali
BTech(ICT), DA-IICT
Gandhinagar