CS255 Syllabus

Example of calling a function

Recall that before you call a function in assembler, you must pass parameter first:

  Code in Java/C/C++:
  ============================================================

  main(...)              ---->  int printf(....)
  {			/	{
     ...	       /	   ...
     ...	      /		   ...
     printf("Hello")	   	   return;
     ^                          }     |
     |  			      |
     +--------------------------------+
     ...
  }


  Assembler code for calling a subroutine/function
  ============================================================

  main:  ...			     
	 ...			
 	 ... 		
	 Pass parameters in output registers
	 call printf
	 nop

	 ...
	 ...
  str1:  .ascii "Hello World!\n\0"

The string parameter in "printf" is actually the address of a string defined in memory:
```
   str1:  .ascii "Hello World!\n\0"
 
```
defines a string in memory. What it actually does is to reserve (enough) space in memory and store the ASCII codes of the characters 'H', 'o', etc. in that space.
To pass the address of this string (in output register o0) to "printf", you use (for the so many time...):
```
    sethi  str1, %o0
    add    %o0, %lo(str1), %o0
 
```
Here is the program: click here
Compile it using:
```
    cc sparc-example1.s
 
```
Run it using:
```
    a.out
 
```
There you have your first "real" program in assembler....