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[cc65] / doc / cc65.txt

                                   cc65

                       A C Compiler for 6502 Systems

                    (C) Copyright 1989 John R. Dunning
               (C) Copyright 1998-2000 Ullrich von Bassewitz
                            (uz@musoftware.de)



Contents
--------

  1. Overview

  2. Usage

  3. Input and output

  4. Differences to the ISO standard

  5. Extensions

  6. Predefined macros

  7. #pragmas

  8. Bugs/Feedback

  9. Copyright



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

cc65 was originally a C compiler for the Atari 8-bit machines written by
John R. Dunning. In prior releases I've described the compiler by listing
up the changes made by me. I have made many more changes in the meantime
(and rewritten major parts of the compiler), so I will no longer do that,
since the list would be too large and of no use to anyone. Instead I will
describe the compiler in respect to the ANSI/ISO C standard. In fact, I'm
planning a complete rewrite (that is, a complete new compiler) for the
next release, since there are too many limitations in the current code,
and removing these limitations would mean a rewrite of many more parts of
the compiler.

There is a separate document named "library.txt" that covers the library
available for the compiler. If you know C and are interested in doing
actual programming, the library documentation is probably of much more use
than this document.

If you need some hints for getting the best code out of the compiler, you
may have a look at "coding.txt" which covers some code generation issues.



2. Usage
--------

The compiler translates C files into files containing assembler code that
may be translated by the ca65 macroassembler (for more information about
the assembler, have a look at ca65.txt).

The compiler may be called as follows:

---------------------------------------------------------------------------
Usage: cc65 [options] file
Short options:
  -d                    Debug mode
  -g                    Add debug info to object file
  -h                    Help (this text)
  -j                    Default characters are signed
  -o name               Name the output file
  -t sys                Set the target system
  -v                    Increase verbosity
  -A                    Strict ANSI mode
  -Cl                   Make local variables static
  -Dsym[=defn]          Define a symbol
  -I dir                Set an include directory search path
  -O                    Optimize code
  -Oi                   Optimize code, inline more code
  -Or                   Enable register variables
  -Os                   Inline some known functions
  -T                    Include source as comment
  -V                    Print the compiler version number
  -W                    Suppress warnings

Long options:
  --ansi                Strict ANSI mode
  --cpu type            Set cpu type
  --debug               Debug mode
  --debug-info          Add debug info to object file
  --help                Help (this text)
  --include-dir dir     Set an include directory search path
  --signed-chars        Default characters are signed
  --static-locals       Make local variables static
  --target sys          Set the target system
  --verbose             Increase verbosity
  --version             Print the compiler version number
---------------------------------------------------------------------------


  -A
  --ansi

  This option disables any compiler exensions. Have a look at section 5
  for a discussion of compiler extensions. In addition, the macro

        __STRICT_ANSI__

  is defined, when using one of these options.


  --cpu CPU

  A new, still experimental option. You may specify "6502" or "65C02" as
  the CPU. 6502 is the default, so this will not change anything.
  Specifying 65C02 will use a few 65C02 instructions when generating code.
  Don't expect too much from this option: It is still new (and may have
  bugs), and the additional instructions for the 65C02 are not that
  overwhelming.


  -d
  --debug

  Enables debug mode, something that should not be needed for mere
  mortals:-)


  -D sym[=definition]

  Define a macro on the command line. If no definition is given, the macro
  is defined to the value "1".


  -g
  --debug-info

  This will cause the compiler to insert a .DEBUGINFO command into the
  generated assembler code. This will cause the assembler to include all
  symbols in a special section in the object file.


  -h
  --help

  Print the short option summary shown above.


  -j
  --signed-chars

  Using this option, you can make the default characters signed. Since the
  6502 has no provisions for sign extending characters (which is needed on
  almost any load operation), this will make the code larger and slower. A
  better way is to declare characters explicitly as "signed" if needed.
  You can also use "#pragma signedchars" for better control of this option
  (see section 7).


  -t target
  --target target

  This option is used to set the target system. The target system
  determines things like the character set that is used for strings and
  character constants. The following target systems are supported:

        none
        c64
        c128
        ace             (no library support)
        plus4
        cbm610
        pet             (all CBM PET systems except the 2001)
        nes             (Nintendo Entertainment System)
        apple2
        geos


  -v
  --verbose

  Using this option, the compiler will be somewhat more verbose if errors
  or warnings are encountered.
 

  -Cl
  --static-locals

  Use static storage for local variables instead of storage on the stack.
  Since the stack is emulated in software, this gives shorter and usually
  faster code, but the code is no longer reentrant. The difference between
  -Cl and declaring local variables as static yourself is, that
  initializer code is executed each time, the function is entered. So when
  using

        void f (void)
        {
            unsigned a = 1;
            ...
        }

  the variable a will always have the value 1 when entering the function
  and using -Cl, while in

        void f (void)
        {
            static unsigned a = 1;
            ....
        }

  the variable a will have the value 1 only the first time, the function
  is entered, and will keep the old value from one call of the function to
  the next.

  You may also use #pragma staticlocals to change this setting in your
  sources (see section 7).


  -I dir
  --include-dir dir

  Set a directory where the compiler searches for include files. You may
  use this option multiple times to add more than one directory to the
  search list.   


  -o name
  
  Specify the name of the output file. If you don't specify a name, the
  name of the C input file is used, with the extension replaced by ".s".


  -O, -Oi, -Or, -Os

  Enable an optimizer run over the produced code.

  Using -Oi, the code generator will inline some code where otherwise a
  runtime functions would have been called, even if the generated code is
  larger. This will not only remove the overhead for a function call, but
  will make the code visible for the optimizer.

  -Or will make the compiler honor the "register" keyword. Local variables
  may be placed in registers (which are actually zero page locations).
  There is some overhead involved with register variables, since the old
  contents of the registers must be saved and restored. In addition, the
  current implementation does not make good use of register variables, so
  using -Or may make your program even slower and larger. Use with care!

  Using -Os will force the compiler to inline some known functions from
  the C library like strlen. Note: This has two consequences:

    * You may not use names of standard C functions in your own code. If
      you do that, your program is not standard compliant anyway, but
      using -Os will actually break things.

    * The inlined string and memory functions will not handle strings or
      memory areas larger than 255 bytes. Similar, the inlined is..()
      functions will not work with values outside char range.

  It is possible to concatenate the modifiers for -O. For example, to
  enable register variables and inlining of known functions, you may use
  -Ors.


  -T

  This include the source code as comments in the generated code. This is
  normally not needed.


  -V   
  --version

  Print the version number of the compiler. When submitting a bug report,
  please include the operating system you're using, and the compiler
  version.
    

  -W

  This option will suppress any warnings generated by the compiler. Since
  any source file may be written in a manner that it will not produce
  compiler warnings, using this option is usually not a good idea.



3. Input and output
-------------------

The compiler will accept one C file per invocation and create a file with
the same base name, but with the extension replaced by ".s". The output
file contains assembler code suitable for the use with the ca65 macro
assembler.

In addition to the paths named in the -I option on the command line, the
directory named in the environment variable CC65_INC is added to the
search path for include files on startup.



4. Differences to the ISO standard
----------------------------------

Here is a list of differences between the language, the compiler accepts,
and the one defined by the ISO standard:


  * The compiler allows single line comments that start with //. This
    feature is disabled in strict ANSI mode.

  * The compiler allows unnamed parameters in parameter lists. The
    compiler will not issue warnings about unused parameters that don't
    have a name. This feature is disabled in strict ANSI mode.

  * The compiler has some additional keywords:

        asm, __asm__, fastcall, __fastcall__, __AX__, __EAX__, __func__,
        __attribute__

    The keywords without the underlines are disabled in strict ANSI mode.

  * The "const" modifier is available, but has no effect.

  * The datatypes "float" and "double" are not available.

  * The compiler does not support bit fields.

  * Initialization of local variables is only possible for scalar data
    types (that is, not for arrays and structs).

  * Because of the "wrong" order of the parameters on the stack, there is
    an additional macro needed to access parameters in a variable
    parameter list in a C function.

  * Functions may not return structs. However, struct assignment *is*
    possible.

  * Part of the C library is available only with fastcall calling
    conventions (see below). This means, that you may not mix pointers to
    those functions with pointers to user written functions.

There may be some more minor differences, I'm currently not aware off. The
biggest problem is the missing float data type. With this limitation in
mind, you should be able to write fairly portable code.



5. Extensions
-------------

This cc65 version has some extensions to the ISO C standard.

  * The compiler allows // comments (like in C++ and in the proposed C9x
    standard). This feature is disabled by -A.

  * The compiler allows to insert assembler statements into the output
    file. The syntax is

        asm (<string literal>) ;

    or

        __asm__ (<string literal>) ;

    The first form is in the user namespace and is disabled if the -A
    switch is given.

    The given string is inserted literally into the output file, and a
    newline is appended. The statements in this string are not checked by
    the compiler, so be careful!

    The asm statement may be used inside a function and on global file
    level.

  * There is a special calling convention named "fastcall". This calling
    convention is currently only usable for functions written in
    assembler. The syntax for a function declaration using fastcall is

        <return type> fastcall <function name> (<parameter list>)

    or

        <return type> __fastcall__ <function name> (<parameter list>)

    An example would be

        void __fastcall__ f (unsigned char c)

    The first form of the fastcall keyword is in the user namespace and is
    therefore disabled in strict ANSI mode.

    For functions declared as fastcall, the rightmost parameter is not
    pushed on the stack but left in the primary register when the function
    is called. This will reduce the cost when calling assembler functions
    significantly, especially when the function itself is rather small.

  * There are two pseudo variables named __AX__ and __EAX__. Both refer to
    the primary register that is used by the compiler to evaluate
    expressions or return function results. __AX__ is of type unsigned int
    and __EAX__ of type long unsigned int respectively. The pseudo
    variables may be used as lvalue and rvalue as every other variable.
    They are most useful together with short sequences of assembler code.
    For example, the macro

        #define hi(x) (__AX__=(x),asm("\ttxa\n\tldx\t#$00",__AX__)

    will give the high byte of any unsigned value.

  * Inside a function, the identifier __func__ gives the name of the
    current function as a string. Outside of functions, __func__ is
    undefined.
    Example:

        #define PRINT_DEBUG(s)  printf ("%s: %s\n", __func__, s);

    The macro will print the name of the current function plus a given
    string.



6. Predefined macros
--------------------

The compiler defines several macros at startup:


  __CC65__        This macro is always defined. Its value is the version
                  number of the compiler in hex. Version 2.0.1 of the
                  compiler will have this macro defined as 0x0201.

  __CBM__         This macro is defined if the target system is one of the
                  CBM targets.

  __C64__         This macro is defined if the target is the c64 (-t c64).

  __C128__        This macro is defined if the target is the c128 (-t c128).

  __PLUS4__       This macro is defined if the target is the plus/4
                  (-t plus4).

  __CBM610__      This macro is defined if the target is one of the CBM
                  600/700 family of computers (called B series in the US).

  __PET__         This macro is defined if the target is the PET family of
                  computers (-t pet).

  __NES__         This macro is defined if the target is the Nintendo
                  Entertainment System (-t nes).

  __ATARI__       This macro is defined if the target is one of the Atari
                  computers (400/800/130XL/800XL). Note that there is no
                  runtime and C library support for atari systems.

  __ACE__         This macro is defined if the target is Bruce Craigs ACE
                  operating system. Note that there is no longer runtime
                  and library support for ACE.

  __APPLE2__      This macro is defined if the target is the Apple ][
                  (-t apple2).

  __GEOS__        This macro is defined if you are compiling for the GEOS
                  system (-t geos).

  __FILE__        This macro expands to a string containing the name of
                  the C source file.

  __LINE__        This macro expands to the current line number.

  __STRICT_ANSI__ This macro is defined to 1 if the -A compiler option was
                  given, and undefined otherwise.

  __OPT__         Is defined if the compiler was called with the -O command
                  line option.

  __OPT_i__       Is defined if the compiler was called with the -Oi command
                  line option.

  __OPT_r__       Is defined if the compiler was called with the -Or command
                  line option.

  __OPT_s__       Is defined if the compiler was called with the -Os command
                  line option.



7. #pragmas
-----------

The compiler understands some pragmas that may be used to change code
generation and other stuff.


#pragma bssseg (<name>)

  This pragma changes the name used for the BSS segment (the BSS segment
  is used to store uninitialized data). The argument is a string enclosed
  in double quotes.

  Note: The default linker configuration file does only map the standard
  segments. If you use other segments, you have to create a new linker
  configuration file.

  Beware: The startup code will zero only the default BSS segment. If you
  use another BSS segment, you have to do that yourself, otherwise
  uninitialized variables do not have the value zero.

  Example:

        #pragma bssseg ("MyBSS")


#pragma codeseg (<name>)

  This pragma changes the name used for the CODE segment (the CODE segment
  is used to store executable code). The argument is a string enclosed in
  double quotes.

  Note: The default linker configuration file does only map the standard
  segments. If you use other segments, you have to create a new linker
  configuration file.

  Example:

        #pragma bssseg ("MyCODE")


#pragma dataseg (<name>)

  This pragma changes the name used for the DATA segment (the DATA segment
  is used to store initialized data). The argument is a string enclosed in
  double quotes.

  Note: The default linker configuration file does only map the standard
  segments. If you use other segments, you have to create a new linker
  configuration file.

  Example:

        #pragma bssseg ("MyDATA")


#pragma rodataseg (<name>)

  This pragma changes the name used for the RODATA segment (the RODATA
  segment is used to store readonly data). The argument is a string
  enclosed in double quotes.

  Note: The default linker configuration file does only map the standard
  segments. If you use other segments, you have to create a new linker
  configuration file.

  Example:

        #pragma bssseg ("MyRODATA")


#pragma regvaraddr (<const int>)

  The compiler does not allow to take the address of register variables.
  The regvaraddr pragma changes this. Taking the address of a register
  variable is allowed after using this pragma, if the argument is not
  zero. Using an argument of zero changes back to the default behaviour.

  Beware: The C standard does not allow taking the address of a variable
  declared as register. So your programs become non-portable if you use
  this pragma. In addition, your program may not work. This is usually the
  case if a subroutine is called with the address of a register variable,
  and this subroutine (or a subroutine called from there) uses itself
  register variables. So be careful with this #pragma.

  Example:

        #pragma regvaraddr(1)   /* Allow taking the address
                                 * of register variables
                                 */


#pragma signedchars (<const int>)

  Changed the signedness of the default character type. If the argument
  is not zero, default characters are signed, otherwise characters are
  unsigned. The compiler default is to make characters unsigned since this
  creates a lot better code.


#pragma staticlocals (<const int>)

  Use variables in the bss segment instead of variables on the stack. This
  pragma changes the default set by the compiler option -Cl. If the argument
  is not zero, local variables are allocated in the BSS segment, leading to
  shorter and in most cases faster, but non-reentrant code.


#pragma zpsym (<name>)

  Tell the compiler that the - previously as external declared - symbol with
  the given name is a zero page symbol (usually from an assembler file).
  The compiler will create a matching import declaration for the assembler.

  Example:

        extern int foo;
        #pragma zpsym ("foo");  /* foo is in the zeropage */



8. Bugs/Feedback
----------------

If you have problems using the compiler, if you find any bugs, or if
you're doing something interesting with the compiler, I would be glad to
hear from you. Feel free to contact me by email (uz@musoftware.de).



9. Copyright
------------

This is the original compiler copyright:

--------------------------------------------------------------------------
  -*- Mode: Text -*-

     This is the copyright notice for RA65, LINK65, LIBR65, and other
  Atari 8-bit programs.  Said programs are Copyright 1989, by John R.
  Dunning.  All rights reserved, with the following exceptions:

      Anyone may copy or redistribute these programs, provided that:

  1:  You don't charge anything for the copy.  It is permissable to
      charge a nominal fee for media, etc.

  2:  All source code and documentation for the programs is made
      available as part of the distribution.

  3:  This copyright notice is preserved verbatim, and included in
      the distribution.

      You are allowed to modify these programs, and redistribute the
  modified versions, provided that the modifications are clearly noted.

      There is NO WARRANTY with this software, it comes as is, and is
  distributed in the hope that it may be useful.

      This copyright notice applies to any program which contains
  this text, or the refers to this file.

      This copyright notice is based on the one published by the Free
  Software Foundation, sometimes known as the GNU project.  The idea
  is the same as theirs, ie the software is free, and is intended to
  stay that way.  Everybody has the right to copy, modify, and re-
  distribute this software.  Nobody has the right to prevent anyone
  else from copying, modifying or redistributing it.

--------------------------------------------------------------------------

In acknowledgment of this copyright, I will place my own changes to the
compiler under the same copyright. Please note however, that the library
and all binutils are covered by another copyright, and that I'm planning
to do a complete rewrite of the compiler, after which the compiler
copyright will also change.

For the list of changes requested by this copyright see newvers.txt.