Processor Register - Application Variable association

I have a very simple problem. I wanna write some assembler code (for SPARC) that directly operates on a single register, called %o1. All I wanna do is to initialise this register with zero, and then increment it with some immediate values. The problem is, how can I output the result in %o1 from a C-application. The skeleton I have looks like that:

  void main()
  {
    int a; 开发者_StackOverflow中文版 

    asm volatile (
        ".text\n\t"
          "mov 0, %o1                   \n\t"
        "add %o1, 1,  %o1             \n\t"
        "add %o1, 2,  %o1             \n\t"
        "add %o1, 3,  %o1             \n\t"
    );    

    // assign content of register %o1 somehow to variable a (a = %o1);

    printf("%i\n", a);
  }

So the question is how do I assign the value of %o1 (which should be 6 by the end of the calculation) to variable a so that it can be printed on the console.

It's compiler dependent. For gcc: http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html

void main()
{
  int a;  

  asm(
    "mov 0, %0                   \n\t"
    "add %0, 1,  %0             \n\t"
    "add %0, 2,  %0             \n\t"
    "add %0, 3,  %0             \n\t"
    : "=r"(a)
  );    

  printf("%i\n", a);
}

Update: looks like gcc do not allow selecting specific registers on SPARC. There is another extension for this: http://gcc.gnu.org/onlinedocs/gcc/Local-Reg-Vars.html

register int a asm ("o1");

This is much depending on your compiler (which you didn't tell us), look up its documentation. For gcc the syntax would be something like

int a __asm("%o1")__ = 78;