Some problem in ARM (armemu.c)

Some problem in ARM (armemu.c)

[libra]

Hello,all

          I am trying to modify the arm file (gdb/sim/arm/armemu.c) to fit my
          research  purpose. In this file(armemu.c), the
          function "ARMul_Emulate32 (ARMul_State * state)" simulate the ARM
          instruction set.

          My question is that when i modify the instrction operation (see
          below 1), and rebuild the gdb, i also write a test program(see
          below 2). Once exexuting the test program(see below 3), the whole
          program halt. I do not know what happen, because i think the
          modifying is simple.


                                                        Thanks a lot!!
                                                        Best Regards!!

          1. the origin code :
             case 0x08:      /* ADD reg */
               ....
               .....
              rhs = DPRegRHS;
              dest = LHS + rhs;
              WRITEDEST (dest);
              break;

              after modifying :
               case 0x08:      /* ADD reg */
               ....
               .....
              rhs = DPRegRHS;
              dest = LHS + rhs + 1; /*add one*/
              WRITEDEST (dest);
              break;

            2. test program :
               #include <stdio.h>
               void main()
               {
                  int a=0,b=1,c=2;
                  a=b+c;
                  printf("the result is %d\n",a);
               }

             3. execution process :

                arm-elf-run a.out
                /*The program halt*/



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Computer Science Department, National Tsing Hua University

Re: Some problem in ARM (armemu.c)

[Daniel Jacobowitz]

On Thu, Dec 09, 2004 at 07:20:51PM +0800, libra wrote:
> Hello,all
> 
>           I am trying to modify the arm file (gdb/sim/arm/armemu.c) to fit my
>           research  purpose. In this file(armemu.c), the
>           function "ARMul_Emulate32 (ARMul_State * state)" simulate the ARM
>           instruction set.
> 
>           My question is that when i modify the instrction operation (see
>           below 1), and rebuild the gdb, i also write a test program(see
>           below 2). Once exexuting the test program(see below 3), the whole
>           program halt. I do not know what happen, because i think the
>           modifying is simple.

Probably something in the startup code from newlib uses addition, and
goes into an infinite loop with your broken addition.

The simulator is part of GDB; you can load a.out into GDB and run it to
see what happens.

-- 
Daniel Jacobowitz