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Combining programs written in high level and assembler languages

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• What is the difference between programs in high level and assembler languages ?

  Answer:

  • Nothing, nada....

  • In fact, programs written in a high level language are often translated into assembler code before it is translated to machine code.

• Then how can you combine programs written in high level and assembler languages ?

  There are many ways to combine programs written in high level and assembler languages:

  • Embed inline assembler code within a fuction

  • Combining functions written in different languages

• Embedding inline assembler code within a fuction

  In most system programming languages (like C or C++), programmer can insert assembler code within a high level language program using spcial compiler directives

  Example in C:

     int x;
  
     main()
     {
        x = 5;
        printf("x = %d\n", x);     /* Print x */
  
        /* x = 0 */
        asm("sethi %hi(x), %l0");
        asm("st    %g0, [%l0 + %lo(x)]");
  
        printf("x = %d\n", x);     /* Print x again... */
     }
  

  Here is a DEMO: click here

• Combining functions written in different languages

  The easiest way to combine programs written in high level and assembler languages is to write functions and combine the functions together.

  The functions are stored in separate files and compiled separately

  The only thing that you need to find out in order to combine functions written in a high level language and in assembler language is HOW the parameters are passed in the high level language.

  How parameters are passed will depends on the system architecture and the compiler

  It takes a bit of detective work to find this out.... what I did was to write some simple functions with different number of parameters, compile them and look at the assembler listing generated by the compiler to see how the compiler pass the parameters.

  Anyway, I will spare you the detective work and just tell you that in the SPARC C compiler, the parameters are passed as follows:

  • First parameter: in register o0
  • Second parameter: in register o1
  • And so on... (in fact, I wrote all SPARC function using this "convention :-))

  Here is a little demo to show you how that is done:

  • Here is a SPARC assembler main function that calls a function "sum" to sum an array: sparc-example3a.s
  • Here is a SPARC assembler sum function that sums an array of integers: sparc-example3b.s
  • Here is a C language main function that calls a function "sum" to sum an array: sparc-example3a-main.c
  • Here is a C language sum function that sums an array of integers: sparc-example3b-sum.c

  Here are the commands you need to use to compile and combine different main and sum functions together:

  • To combine the SPARC assembler main function with the C language sum function, do:

        cc sparc-example3a.s sparc-example3b-sum.c /home/cs255000/lib/sparclib.o
      

    Note: you need to compile in the /home/cs255000/lib/sparclib.o file because the SPARC assmbler main function calls Write, WriteInt and WriteLn function from my SPARC programming library (that I wrote to simplify SPARC input/output operations)

  • To combine the C language main function with the SPARC assembler language sum function, do:

        cc sparc-example3a-main.c sparc-example3b.c
      

    Here, you don't need my SPARC programming library because the main function uses C library's "printf" function.

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• Passing more than 6 parameters to the caller function
  • Just do what you have learned in: click here

  • Summary:
    1. Pre-allocate space on stack
    2. Pass 7th parameter and beyond using the pre-allocated stack space

  • Parameter location must be as follows (to comply with C-compiler):
    • 7th parameter is passed in [%sp + 92]
    • 8th parameter is passed in [%sp + 96]
    • 9th parameter is passed in [%sp + 100]
    • 10th parameter is passed in [%sp + 106]
    • and so on

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  • Illustration:                                                                                                
    • C main prog that passes 10 parameter to function "Add10": click here
    • SPARC assembler main prog that passes 10 parameter to function "Add10": click here

    • C "Add10" function: click here
    • SPARC assembler "Add10" function: click here

    You can mix and match by combining:

    • C main function calling SPARC assembler function Add10:         cc   C-sparc-10-Params.c   sparc-Add10.s
    • SPARC assembler main function calling C function Add10:         cc   sparc-10-Params.s   C-sparc-Add10.c

    The resulting executable is: a.out