cc65/doc/intro.txt

	     	      How to use the cc65 C compiler

		     Ullrich von Bassewitz, 1998/1999



Contents
--------

  1. Overview

  2. The compiler

  3. The assembler

  4. The linker

  5. The easy way (using the cl65 utility)



1. Overview
-----------

This is a short intro, how to use the compiler and the binutils. It
contains a step-by-step example, how to build a complete application from
one C and one assembler module. This file does *NOT* contain a complete
reference for the tools used in the process. There are separate files
describing these tools in detail.

Note: There is a much simpler way to compile this example using the cl65
compiler and link utility. However, it makes sense to understand how the
separate steps work. How to do the example with the cl65 utility is
described in section 5.

To explain the development flow, I will use the following example modules:


hello.c:

	#include <stdio.h>
	#include <stdlib.h>

       	extern const char text[];	/* In text.s */

	int main (void)
	{
	    printf ("%s\n", text);
	    return EXIT_SUCCESS;
	}


text.s:

	.export	_text
	_text:	.asciiz	"Hello world!"


(The example is rather stupid, since the text in text.s does not use the
correct character set for the target machine - conversion is usually done
by the compiler. However, we will ignore that here.)

We assume that the target file should be named "hello", and the target
system is the C64.


    +---------+
    | hello.c |
    +---------+
       	 |
        cc65
       	 \/
    +---------+	      +---------+
    | hello.s |       | text.s  |
    +---------+	      +---------+
       	 |     	           |
        ca65              ca65
         \/                \/
    +---------+       +---------+      	+----------+   	   +---------+
    | hello.o |       | text.o  |       |  c64.o   |       | c64.lib |
    +---------+       +---------+      	+----------+       +---------+
	 |   		       \         /   	       	       	|
	 |   		       	\       /   			|
	 |   		  	 \     / 			|
	 +----------------------->ld65<-------------------------+
	     		  	   \/
	     		  	  hello


c64.o (the startup code) and c64.lib (the c64 version of the runtime and C
library) are provided in binary form in the cc65 package.



2. The compiler
---------------

The compiler translates one C source into one assembler source for each
invocation. It does *NOT* create object files directly, and it is *NOT*
able to translate more than one file per run.

In the example above, we would use the following command line, to
translate hello.c into hello.s:

	cc65 -O -I ../include -t c64 hello.c

The -O switch tells the compiler to do an additional optimizer run, which
is usually a good idea, since it makes the code smaller. If you don't care
about the size, but want to have slightly faster code, use -Oi to inline
some runtime functions.

The -I switch gives a search path for the include files. You may also set
the environment variable CC65_INC to the search path.

The -t switch is followed by the target system.

If the compiler does not complain about errors in our hello world, we will
have a file named "hello.s" in our directory that contains the assembler
source for the hello module.

For more information about the compiler see cc65.txt.



3. The assembler
----------------

The assembler translates one assembler source into an object file for each
invocation. The assembler is *NOT* able to translate more than one source
file per run.

Let's translate the hello.s and text.s files from our example:

	ca65 hello.s
	ca65 text.s

If the assembler does not complain, we should now have two object files
(named hello.o and text.o) in the current directory.

For more information about the assembler see ca65.txt.



4. The linker
-------------

The linker combines several object and library file into one output file.
ld65 is very configurable, but fortunately has a builtin configuration for
the C64, so we don't need to mess with configuration files here.

The compiler uses small functions to do things that cannot be done inline
without big impact on code size. These runtime functions, together with
the C library are in an object file archive named after the system, in
this case "c64.lib". We have to specify this file on the command line so
that the linker can resolve these functions.

A second file (this time an object file) needed, is the startup code that
prepares the grounds for the C program to run. The startup file must be
executed first, so it must be the first file on the linker command line.

Let's link our files to get the final executable:

       	ld65 -t c64 -o hello c64.o hello.o text.o c64.lib

The argument after -o specifies the name of the output file, the argument
after -t gives the target system. As discussed, the startup file must be the
first file on the command line (you may have to add a path here, if c64.o is
not in your current directory). Since the library resolves imports in hello.o
and text.o, it must be specified *after* these files.

After a successful linker run, we have a file named "hello", ready for our
C64!

For more information about the linker see ld65.txt.



5. The easy way (using the cl65 utility)
----------------------------------------

The cl65 utility is able to do all of the steps described above in just
one call, and it has defaults for some options that are very well suited
for our example.

To compile both files into one executable enter

	cl65 -O -I ../include hello.c test.s

(The -I switch is not needed if you are working under Linux with the
include files in the default path, or the CC65_INC environment variable is
set correctly).

The cl65 utility knows, how to translate C files into object files (it
will call the compiler and then the assembler). It does also know how to
create object files from assembler files (it will call the assember for
that). It knows how to build an executable (it will pass all object files
to the linker). And, finally, it has the C64 as a default target and will
supply the correct startup file and runtime library names to the linker,
so you don't have to care about that.

The one-liner above should give you a C64 executable named "hello" in the
current directory.

For more information about the compile & link utility see cl65.txt.