cc65 Users Guide

Ullrich von Bassewitz,
Greg King

cc65 is a C compiler for 6502 targets. It supports several 6502-based home computers such as the Commodore and Atari machines, but it easily is retargetable.

4. Differences to the ISO standard

10. Implementation-defined behavior

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.

There are separate documents named library.html and funcref.html that cover the library that is 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.html which covers some code generation issues.

2. Usage

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

2.1 Command line option overview

The compiler may be called as follows:


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

Long options:
  --add-source                  Include source as comment
  --all-cdecl                   Make functions default to __cdecl__
  --bss-name seg                Set the name of the BSS segment
  --check-stack                 Generate stack overflow checks
  --code-name seg               Set the name of the CODE segment
  --codesize x                  Accept larger code by factor x
  --cpu type                    Set cpu type (6502, 65c02)
  --create-dep name             Create a make dependency file
  --create-full-dep name        Create a full make dependency file
  --data-name seg               Set the name of the DATA segment
  --debug                       Debug mode
  --debug-info                  Add debug info to object file
  --debug-opt name              Configure optimizations with a file
  --debug-opt-output            Debug output of each optimization step
  --dep-target target           Use this dependency target
  --disable-opt name            Disable an optimization step
  --eagerly-inline-funcs        Eagerly inline some known functions
  --enable-opt name             Enable an optimization step
  --help                        Help (this text)
  --include-dir dir             Set an include directory search path
  --inline-stdfuncs             Inline some standard functions
  --list-opt-steps              List all optimizer steps and exit
  --list-warnings               List available warning types for -W
  --local-strings               Emit string literals immediately
  --memory-model model          Set the memory model
  --register-space b            Set space available for register variables
  --register-vars               Enable register variables
  --rodata-name seg             Set the name of the RODATA segment
  --signed-chars                Default characters are signed
  --standard std                Language standard (c89, c99, cc65)
  --static-locals               Make local variables static
  --target sys                  Set the target system
  --verbose                     Increase verbosity
  --version                     Print the compiler version number
  --writable-strings            Make string literals writable
---------------------------------------------------------------------------

2.2 Command line options in detail

Here is a description of all the command line options:

--all-cdecl

Tells the compiler that functions which aren't declared explicitly with either the __cdecl__ or __fastcall__ calling conventions should have the cdecl convention. (Normally, functions that aren't variadic are fast-called.)

--bss-name seg

Set the name of the bss segment. See also #pragma bss-name.

--check-stack

Tells the compiler to generate code that checks for stack overflows. See #pragma check-stack for an explanation of this feature.

--code-name seg

Set the name of the code segment. See also #pragma code-name

--codesize x

This options allows finer control about speed vs. size decisions in the code generation and optimization phases. It gives the allowed size increase factor (in percent). The default is 100 when not using -Oi and 200 when using -Oi (-Oi is the same as -O --codesize 200).

--cpu CPU

Set the CPU, the compiler generates code for. You may specify "6502" or "65C02" as the CPU. The default depends on the selected target (see option -t). It is the 6502 CPU for most targets or if no target has been set. Specifying 65C02 will use a few 65C02 instructions when generating code. Don't expect too much from this option: In most cases the difference in size and speed is just 1-2%.

--create-dep name

Tells the compiler to generate a file containing the dependency list for the compiled module in makefile syntax. The output is written to a file with the given name. The output does not include system include files (in angle brackets).

--create-full-dep name

--data-name seg

Set the name of the data segment. See also #pragma data-name

-d, --debug

Enables debug mode, for debugging the behavior of cc65.

--debug-tables name

Writes symbol table information to a file, which includes details on structs, unions functions, and global variables. For example, given the following code:


  struct l {
      unsigned char m;
      unsigned char n;
  };

  struct hello {
      unsigned char j;
      unsigned char k;
      struct l l;
  };

  struct sub {
      unsigned char x;
      unsigned char y;
  };

  union xy {
      struct sub xy;
      unsigned int mem;
  };

  typedef struct hello thingy;

  unsigned char single;

  unsigned char test_local_vars_main(void) {
      static unsigned char wahoo;
      static unsigned char bonanza = 0x42;
      unsigned char i;
      unsigned int j;
      unsigned int *random;
      unsigned char *lol;
      signed char whoa;
      struct hello wow;
      thingy *cool;
      union xy xy;

      return 0;
  }

The following output would be produced:


  SC_FUNC: _test_local_vars_main: Symbol table
  ============================================
  __fixargs__:
      Flags: SC_CONST SC_DEF
      Type:  unsigned int
  __argsize__:
      Flags: SC_CONST SC_DEF
      Type:  unsigned char
  wahoo:
      AsmName: M0001
      Flags: SC_STATIC SC_DEF SC_REF
      Type:  unsigned char
  bonanza:
      AsmName: M0002
      Flags: SC_STATIC SC_DEF SC_REF
      Type:  unsigned char
  i:
      Flags: SC_AUTO SC_DEF SC_REF
      Type:  unsigned char
  j:
      Flags: SC_AUTO SC_DEF SC_REF
      Type:  unsigned int
  random:
      Flags: SC_AUTO SC_DEF SC_REF
      Type:  unsigned int *
  lol:
      Flags: SC_AUTO SC_DEF SC_REF
      Type:  unsigned char *
  whoa:
      Flags: SC_AUTO SC_DEF SC_REF
      Type:  signed char
  wow:
      Flags: SC_AUTO SC_DEF SC_REF
      Type:  struct hello
  cool:
      Flags: SC_AUTO SC_DEF SC_REF
      Type:  struct hello *
  xy:
      Flags: SC_AUTO SC_DEF SC_REF
      Type:  union xy




  Global symbol table
  ===================
  thingy:
      AsmName: _thingy
      Flags: SC_TYPEDEF 0x100000
      Type:  struct hello
  single:
      AsmName: _single
      Flags: SC_STATIC SC_EXTERN SC_STORAGE SC_DEF SC_REF 0x100000
      Type:  unsigned char
  test_local_vars_main:
      AsmName: _test_local_vars_main
      Flags: SC_FUNC SC_STATIC SC_EXTERN SC_DEF 0x100000
      Type:  unsigned char (void)




  Global tag table
  ================
  l:
      Flags: SC_STRUCT SC_DEF
      Type:  (none)
  hello:
      Flags: SC_STRUCT SC_DEF
      Type:  (none)
  sub:
      Flags: SC_STRUCT SC_DEF
      Type:  (none)
  xy:
      Flags: SC_UNION SC_DEF
      Type:  (none)




  Global struct and union definitions
  =========================

  SC_STRUCT: l
  ============
  m:
      Flags: SC_STRUCTFIELD
      Type:  unsigned char
  n:
      Flags: SC_STRUCTFIELD
      Type:  unsigned char




  SC_STRUCT: hello
  ================
  j:
      Flags: SC_STRUCTFIELD
      Type:  unsigned char
  k:
      Flags: SC_STRUCTFIELD
      Type:  unsigned char
  l:
      Flags: SC_STRUCTFIELD
      Type:  struct l




  SC_STRUCT: sub
  ==============
  x:
      Flags: SC_STRUCTFIELD
      Type:  unsigned char
  y:
      Flags: SC_STRUCTFIELD
      Type:  unsigned char




  SC_UNION: xy
  ============
  xy:
      Flags: SC_STRUCTFIELD
      Type:  struct sub
  mem:
      Flags: SC_STRUCTFIELD
      Type:  unsigned int

--debug-opt name

The named file contains a list of specific optimization steps to enable or disable. Each line contains the name of an optimization step with either a + (enable) or - (disable) prefix. The name all can be used to enable or disable all optimizations. Comment lines may begin with # or ;.

Use --list-opt-steps to generate a complete list of available optimization steps.

Use --debug to see a list of optimizations applied during compilation.

--debug-opt-output

For debugging the output of each optimization pass, step by step. Generates a name.opt output listing for each optimized function name.

--dep-target target

When generating a dependency file, don't use the actual output file as the target of the dependency, but the file specified with this option. The option has no effect if neither --create-dep nor --create-full-dep is specified.

-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.

--eagerly-inline-funcs

Have the compiler eagerly inline these functions from the C library:

memcpy()
memset()
strcmp()
strcpy()
strlen()

Note: This has two consequences:

You may not use names of standard C functions for your own functions. If you do that, your program is not standard-compliant anyway; but, using --eagerly-inline-funcs actually will break things.
The inlined string and memory functions will not handle strings or memory areas larger than 255 bytes.

--eagerly-inline-funcs implies the --inline-stdfuncs command line option.

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 use with the ca65 macro assembler.

Include files in quotes are searched in the following places:

The current file's directory.
Any directory added with the -I option on the command line.
The value of the environment variable CC65_INC if it is defined.

Include files in angle brackets are searched in the following places:

Any directory added with the -I option on the command line.
The value of the environment variable CC65_INC if it is defined.
A subdirectory named include of the directory defined in the environment variable CC65_HOME, if it is defined.
An optionally compiled-in directory.

4. Differences to the ISO standard

Apart from the things listed below, the compiler does support additional keywords, has several functions in the standard headers with names outside the reserved namespace and a few syntax extensions. All these can be disabled with the --standard command line option. Its use for maximum standards compatibility is advised.

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

The datatypes "float" and "double" are not available. Floating point constants may be used, though they will have to be converted and stored into integer values. Floating point arithmetic expressions are not supported.
C Functions may pass and return structs (or unions) by value, but only of 1, 2 or 4 byte sizes.
Most of the C library is available with only the fastcall calling convention ( see below). It means that you must not mix pointers to those functions with pointers to user-written, cdecl functions (the calling conventions are incompatible).
The volatile keyword has almost no effect. That is not as bad as it sounds, since the 6502 has so few registers that it isn't possible to keep values in registers anyway.

There may be some more minor differences I'm currently not aware of. 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 to insert inline assembler code in the form of the asm expression into the output file. The syntax is
asm [optional volatile] (<string literal>[, optional parameters])
or
__asm__ [optional volatile] (<string literal>[, optional parameters])
The first form is in the user namespace; and, is disabled if the -A switch is given. There is a whole section covering the inline assembler, see there.
The normal calling convention -- for non-variadic functions -- is named "fastcall". The syntax for a function declaration that explicitly uses fastcall is
<return type> fastcall <function name> (<parameter list>)
or
<return type> __fastcall__ <function name> (<parameter list>)
An example is
void __fastcall__ f (unsigned char c)
The first form of the fastcall keyword is in the user namespace and can therefore be disabled with the --standard command line option. For functions that are fastcall, the rightmost parameter is not pushed on the stack but left in the primary register when the function is called. That significantly reduces the cost of calling those functions.
There is another calling convention named "cdecl". Variadic functions (their prototypes have an ellipsis [...]) always use that convention. The syntax for a function declaration using cdecl is
<return type> cdecl <function name> (<parameter list>)
or
<return type> __cdecl__ <function name> (<parameter list>)
An example is
int* __cdecl__ f (unsigned char c)
The first form of the cdecl keyword is in the user namespace; and therefore, can be disabled with the --standard command-line option. For functions that are cdecl, the rightmost parameter is pushed onto the stack before the function is called. That increases the cost of calling those functions, especially when they are called from many places.
There are three pseudo variables named __A__, __AX__ and __EAX__. They all refer to the primary register that is used by the compiler to evaluate expressions or return function results. __A__ is of type unsigned char, __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 ("txa"), \ asm ("ldx #$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.
cc65 allows the initialization of void variables. This may be used to create arbitrary structures that are more compatible with interfaces written for assembler languages. Here is an example:
void GCmd = { (char)3, (unsigned)0x2000, (unsigned)0x3000 };
That will be translated as follows:
_GCmd: .byte 3 .word $2000 .word $3000
Since the variable is of type void, you may not use it as-is. However, taking the address of the variable results in a void* which may be passed to any function expecting a pointer. Also, the sizeof operator will give the length of the initializer:
GLen = sizeof GCmd;
will assign the value 5 to GLen. See the GEOS library document for examples on how to use that feature.
cc65 implements flexible array struct members as defined in the C99 ISO standard. As an extension, these fields may be initialized. There are several exceptions, however (which is probably the reason why the standard does not define this feature, because it is highly unorthogonal). Flexible array members cannot be initialized ...
- ... when defining an array of structs with flexible members.
- ... if such a struct is a member field of another struct which is not the last field.
- ... if the struct which contains a flexible array member is declared as register, and the size and compiler settings do allow the compiler actually to place the struct into the register bank in the zero page.
Please note that -- as defined in the ISO C standard -- the sizeof operator returns the struct size with the flexible array member having size zero, even if it is initialized.
cc65 supports _Static_assert from C11 and C2X. This is similar to #error but happens at a later stage of translation, so types can be used.
/* C11 version with message. */ _Static_assert (sizeof (int) == 2, "Expected 2-bytes ints."); /* C2X version without message. */ _Static_assert (sizeof (int) == 2);
_Static_assert is also available as the macro static_assert in assert.h. Note: The string literal as the message in the _Static_assert declaration is not subject to string literal translation (see #pragma charmap()) and will always be in the host encoding. On the other hand, any character or string literals present in the condition expression of the _Static_assert declaration will be translated as usual.
cc65 supports bit-fields of any integral type that is int-sized or smaller, and enumerated types with those types as their underlying type. (Only int, signed int, and unsigned int are required by the standard.)
Computed gotos, a GCC extension, has limited support. With it you can use fast jump tables from C. You can take the address of a label with a double ampersand, putting them in a static const array of type void *. Then you can jump to one of these labels as follows:
static const void * const jumptable[] = { &&add, &&sub }; goto *jumptable[somevar]; add: ...code...
In the jump table, no expressions are supported. The array index used in the goto must be a simple variable or a constant.
Binary literals, a C++14 feature and a GCC C extension, are accepted. They can be disabled with the --standard option.
unsigned char foo = 0b101; // sets it to 5

6. Predefined macros

The compiler defines several macros at startup:

__APPLE2__

This macro is defined if the target is the Apple ][ (-t apple2) or the enhanced Apple //e (-t apple2enh).

__APPLE2ENH__

This macro is defined if the target is the enhanced Apple //e (-t apple2enh).

__ATARI2600__

This macro is defined if the target is the Atari 2600 game console.

__ATARI5200__

This macro is defined if the target is the Atari 5200 game console.

__ATARI__

This macro is defined if the target is the Atari 400/800 (-t atari) or the Atari 800XL/130XE (-t atarixl).

__ATARIXL__

This macro is defined if the target is the Atari 800XL/130XE (-t atarixl).

__ATMOS__

This macro is defined if the target is the Oric Atmos (-t atmos).

__C128__

This macro is defined if the target is the Commodore 128 (-t c128).

__C16__

This macro is defined if the target is the Commodore 16/116 (-t c16) or the Commodore Plus/4 (-t plus4).

__C64__

This macro is defined if the target is the Commodore 64 (-t c64).

__CBM__

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

__CBM510__

This macro is defined if the target is the CBM 500 series of computers.

__CBM610__

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

__CC65__

This macro is always defined. Its value is the version number of the compiler in hex: (VER_MAJOR * 0x100) + VER_MINOR. The upper 8 bits are the major-, the lower 8 bits are the minor version. For example, version 47.11 of the compiler would have this macro defined as 0x2f0b.

Note: until 2.19 this macro was defined as (VER_MAJOR * 0x100) + VER_MINOR * 0x10 - which resulted in broken values starting at version 2.16 of the compiler. For this reason the value of this macro is considered purely informal - you should not use it to check for a specific compiler version and use different code according to the detected version - please update your code to work with the recent version of the compiler instead (There is very little reason to not use the most recent version - and even less to support older versions in your code).

Should you still insist on doing this for some reason - look at checkversion.c in the samples directory for some preprocessor kludges that might help.

__CC65_STD__

This macro is defined to one of the following depending on the --standard command line option:

__CC65_STD_C89__
__CC65_STD_C99__
__CC65_STD_CC65__

__CX16__

This macro is defined if the target is the Commander X16 (-t cx16).

__DATE__

This macro expands to the date of translation of the preprocessing translation unit in the form "Mmm dd yyyy".

__EAGERLY_INLINE_FUNCS__

Is defined if the compiler was called with the --eagerly-inline-funcs command line option.

__FILE__

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

__GEOS__

This macro is defined if you are compiling for one of the GEOS systems.

__GEOS_APPLE__

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

__GEOS_CBM__

This macro is defined if you are compiling for the GEOS 64/128 system (-t geos-cbm).

__LINE__

This macro expands to the current line number.

__LUNIX__

This macro is defined if you are compiling for the LUnix system (-t lunix).

__LYNX__

This macro is defined if the target is the Atari Lynx (-t lynx).

__NES__

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

__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.

__OSIC1P__

This macro is defined if the target is the Ohio Scientific Challenger 1P (-t osic1p).

__PET__

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

__PLUS4__

This macro is defined if the target is the Commodore Plus/4 (-t plus4).

__SIM6502__

This macro is defined if the target is sim65 in 6502 mode (-t sim6502).

__SIM65C02__

This macro is defined if the target is sim65 in 65C02 mode (-t sim65c02).

__STDC_HOSTED__

This macro expands to the integer constant 1.

__STDC_NO_ATOMICS__

This macro expands to the integer constant 1 if the language standard is cc65 (--standard cc65).

__STDC_NO_COMPLEX__

This macro expands to the integer constant 1 if the language standard is cc65 (--standard cc65).

__STDC_NO_THREADS__

This macro expands to the integer constant 1 if the language standard is cc65 (--standard cc65).

__STDC_NO_VLA__

This macro expands to the integer constant 1 if the language standard is cc65 (--standard cc65).

__SUPERVISION__

This macro is defined if the target is the Supervision (-t supervision).

__SYM1__

This macro is defined if the target is the Sym-1 (-t sym1).

__TELESTRAT__

This macro is defined if the target is the Telestrat (-t telestrat).

__TIME__

This macro expands to the time of translation of the preprocessing translation unit in the form "hh:mm:ss".

__VIC20__

This macro is defined if the target is the Commodore VIC20 (-t vic20).

7. #pragmas

The compiler understands some pragmas that may be used to change code generation and other stuff. Some of these pragmas understand a special form: If the first parameter is push, the old value is saved onto a stack before changing it. The value may later be restored by using the pop parameter with the #pragma.

7.1 `#pragma allow-eager-inline ([push,] on|off)`

Allow eager inlining of known functions. If the argument is "off", eager inlining is disabled, otherwise it is enabled. Please note that (in contrast to the --eagerly-inline-funcs command line option) this pragma does not imply the --inline-stdfuncs command line option. Rather it marks code to be safe for eager inlining of known functions if inlining of standard functions is enabled.

The #pragma understands the push and pop parameters as explained above.

7.2 `#pragma bss-name ([push, ]<name>[ ,<addrsize>])`

This pragma changes the name used for the BSS segment (the BSS segment is used to store variables with static storage duration and no explicit initializers). The name argument is a string enclosed in quotation marks.

addrsize is an optional string that gives a hint about where the name segment will be put in the CPU's address space. It describes the width of address numbers that point into that segment. Only words that are known to ca65 are allowed:

"zp", "zeropage", "direct"
"abs", "absolute", "near", "default"
"far"
"long", "dword"

Note: The default linker configuration file maps only the standard segments. If you use other segments, you must create a new linker configuration file.

Beware: The start-up code will zero only the default BSS segment. If you use another BSS segment, then you must do that yourself; otherwise, variables with static storage duration and no explicit initializer will not have the value zero.

The #pragma understands the push and pop parameters, as explained above.

Examples:


  #pragma bss-name ("MyBSS")
  #pragma bss-name (push, "MyBSS")
  #pragma bss-name ("MyBSS", "zp")

7.3 `#pragma charmap (<index>, <code>)`

Each literal string and each literal character in the preprocessed source, except when used in an asm expression as the inline assembler code or in a _Static_assert declaration as the failure message, is translated by use of a translation table. That translation table is preset when the compiler is started, depending on the target system; for example, to map ISO-8859-1 characters into PETSCII if the target is a Commodore machine.

This pragma allows to change entries in the translation table, so the translation for individual characters, or even the complete table may be adjusted. Both arguments are assumed to be unsigned characters with a valid range of 0-255.

Beware of some pitfalls:

The character index is actually the code of the character in the C source; so, character mappings do always depend on the source character set. That means that #pragma charmap() is not portable -- it depends on the build environment.
While it is possible to use character literals as indices, the result may be somewhat unexpected, since character literals are themselves translated. For that reason, I would suggest to avoid character literals, and use numeric character codes instead.
It is risky to change index 0x00, because string functions depend on it. If it is changed, then the '\0' at the end of string literals will become non-zero. Functions that are used on those literals won't stop at the end of them. cc65 will warn you if you do change that code number. You can turn off that remap-zero warning if you are certain that you know what you are doing (see #pragma warn()).

Example:


  /* Use a space wherever an 'a' occurs in ISO-8859-1 source */
  #pragma charmap (0x61, 0x20);

7.4 `#pragma check-stack ([push,] on|off)`

Tells the compiler to insert calls to a stack checking subroutine to detect stack overflows. The stack checking code will lead to somewhat larger and slower programs, so you may want to use this pragma when debugging your program and switch it off for the release version. If a stack overflow is detected, the program is aborted.

If the argument is "off", stack checks are disabled (the default), otherwise they're enabled.

The #pragma understands the push and pop parameters as explained above.

7.5 `#pragma code-name ([push, ]<name>[ ,<addrsize>])`

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

"zp", "zeropage", "direct"
"abs", "absolute", "near", "default"
"far"
"long", "dword"

Note: The default linker configuration file maps only the standard segments. If you use other segments, you must create a new linker configuration file.

The #pragma understands the push and pop parameters, as explained above.

Examples:


  #pragma code-name ("MyCODE")
  #pragma code-name (push, "MyCODE")
  #pragma code-name (push, "MyCODE", "far")

7.6 `#pragma codesize ([push,] <int>)`

This pragma allows finer control about speed vs. size decisions in the code generation and optimization phase. It gives the allowed size increase factor (in percent). The default is can be changed by use of the --codesize compiler option.

The #pragma understands the push and pop parameters as explained above.

7.7 `#pragma data-name ([push, ]<name>[ ,<addrsize>])`

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

"zp", "zeropage", "direct"
"abs", "absolute", "near", "default"
"far"
"long", "dword"

Note: The default linker configuration file maps only the standard segments. If you use other segments, you must create a new linker configuration file.

The #pragma understands the push and pop parameters, as explained above.

Examples:


  #pragma data-name ("MyDATA")
  #pragma data-name (push, "MyDATA")
  #pragma data-name ("MyDATA", "zeropage")

7.8 `#pragma inline-stdfuncs ([push,] on|off)`

Allow the compiler to inline some standard functions from the C library like strlen. If the argument is "off", inlining is disabled, otherwise it is enabled.

See also the --inline-stdfuncs command line option.

The #pragma understands the push and pop parameters as explained above.

7.9 `#pragma local-strings ([push,] on|off)`

When "on", emit string literals to the data segment when they're encountered in the source. The default ("off") is to keep string literals until end of assembly, merge read only literals if possible, and then output the literals into the data or rodata segment that is active at that point.

Using this #pragma it is possible to control the behaviour from within the source. When #pragma local-strings is active, string literals are output immediately, which means that they go into the currently active data or rodata segment, but cannot be merged. When inactive, string literals are remembered and output as a whole when translation is finished.

7.10 `#pragma message (<message>)`

This pragma is used to display informational messages at compile-time.

The message intended to be displayed must be a string literal.

Example:


        #pragma message ("in a bottle")

Results in the compiler outputting the following to stderr:


        example.c(42): Note: in a bottle

7.11 `#pragma optimize ([push,] on|off)`

Switch optimization on or off. If the argument is "off", optimization is disabled, otherwise it is enabled. Please note that this pragma only effects whole functions. The setting in effect when the function is encountered will determine if the generated code is optimized or not.

Optimization and code generation is also controlled by the codesize pragma.

The default is "off", but may be changed with the -O compiler option.

The #pragma understands the push and pop parameters as explained above.

7.12 `#pragma rodata-name ([push, ]<name>[ ,<addrsize>])`

This pragma changes the name used for the RODATA segment (the RODATA segment is used to store read-only data). The name argument is a string enclosed in quotation marks.

"zp", "zeropage", "direct"
"abs", "absolute", "near", "default"
"far"
"long", "dword"

Note: The default linker configuration file maps only the standard segments. If you use other segments, you must create a new linker configuration file.

The #pragma understands the push and pop parameters, as explained above.

Examples:


  #pragma rodata-name ("MyRODATA")
  #pragma rodata-name (push, "MyRODATA")

7.13 `#pragma regvaraddr ([push,] on|off)`

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 with "on" as argument. Using "off" as an argument switches 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 register variables. So be careful with this #pragma.

The #pragma understands the push and pop parameters as explained above.

Example:


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

7.14 `#pragma register-vars ([push,] on|off)`

Enables or disables use of register variables. If register variables are disabled (the default), the register keyword is ignored. Register variables are explained in more detail in a separate chapter.

The #pragma understands the push and pop parameters as explained above.

7.15 `#pragma signed-chars ([push,] on|off)`

Changes the signedness of the default character type. If the argument is "on", default characters are signed, otherwise characters are unsigned. The compiler default is to make characters unsigned since this creates a lot better code. This default may be overridden by the --signed-chars command line option.

The #pragma understands the push and pop parameters as explained above.

7.16 `#pragma static-locals ([push,] on|off)`

Use variables in the bss segment instead of variables on the stack. This pragma changes the default set by the compiler option --static-locals. If the argument is "on", local variables are allocated in the BSS segment, leading to shorter and in most cases faster, but non-reentrant code.

The #pragma understands the push and pop parameters as explained above.

7.17 `#pragma warn (name, [push,] on|off)`

Switch compiler warnings on or off. "name" is the name of a warning (see the -W compiler option for a list). The name is followed either by "pop", which restores the last pushed state, or by "on" or "off", optionally preceded by "push" to push the current state before changing it.

Example:


        /* Don't warn about the unused parameter in function func */
        #pragma warn (unused-param, push, off)
        static int func (int unused)
        {
            return 0;
        }
        #pragma warn (unused-param, pop)

7.18 `#pragma wrapped-call (push, <name>, <identifier>)`

This pragma sets a wrapper for functions, often used for trampolines.

The name is a wrapper function returning void, and taking no parameters. It must preserve the CPU's A and X registers if it wraps any __fastcall__ functions that have parameters. It must preserve the Y register if it wraps any variadic functions (they have "..." in their prototypes).

The identifier is an 8-bit number that's set into tmp4. If the identifier is "bank", then ca65's .bank function will be used to determine the number from the bank attribute defined in the linker config, see Other MEMORY area attributes. Note that this currently implies that only the least significant 8 bits of the bank attribute can be used.

The address of a wrapped function is passed in ptr4. The wrapper can call that function by using "jsr callptr4".

All functions ever declared or defined when this pragma is in effect will be wrapped when they are called explicitly by their names later in the same translation unit. Invocation of these functions in any other ways, for example, that via a function pointer or in inline assembly code, will not be wrapped.

This feature is useful, for example, with banked memory, to switch banks automatically to where a wrapped function resides, and then to restore the previous bank when it returns.

The #pragma requires the push or pop argument as explained above.

Example:


/* Note that this code can be in a header. */
void mytrampoline(void); /* Doesn't corrupt __AX__ */

#pragma wrapped-call (push, mytrampoline, 5)
void somefunc1(void);
void somefunc2(int, char *);
#pragma wrapped-call (pop)

7.19 `#pragma writable-strings ([push,] on|off)`

Changes the storage location of string literals. For historical reasons, the C standard defines that string literals are of type "char[]", but writing to such a literal causes undefined behaviour. Most compilers (including cc65) place string literals in the read-only data segment, which may cause problems with old C code that writes to string literals.

Using this pragma (or the corresponding command line option --writable-strings) causes the literals to be placed in the data segment so they can be written to without worry.

The #pragma understands the push and pop parameters as explained above.

7.20 `#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. Register variables

The runtime for all supported platforms has 6 bytes of zero page space available for register variables (this could be increased, but I think it's a good value). So you can declare register variables up to a total size of 6 per function. The compiler will allocate register space on a "first come, first served" base and convert any register declarations that exceed the available register space silently to auto. Parameters can also be declared as register, this will in fact give slightly shorter code than using a register variable.

Since a function must save the current values of the registers on entry and restore them on exit, there is an overhead associated with register variables, and this overhead is quite high (about 20 bytes per variable). This means that just declaring anything as register is not a good idea.

The best use for register variables are pointers, especially those that point to structures. The magic number here is about 3 uses of a struct field: If the function contains this number or even more, the generated code will be usually shorter and faster when using a register variable for the struct pointer. The reason for this is that the register variable can in many cases be used as a pointer directly. Having a pointer in an auto variable means that this pointer must first be copied into a zero page location, before it can be dereferenced.

Second best use for register variables are counters. However, there is not much difference in the code generated for counters, so you will need at least 100 operations on this variable (for example in a loop) to make it worth the trouble. The only savings you get here are by the use of a zero page variable instead of one on the stack or in the data segment.

Register variables must be explicitly enabled, either by using -Or or --register-vars on the command line or by use of #pragma register-vars. Register variables are only accepted on function top level, register variables declared in interior blocks are silently converted to auto. With register variables disabled, all variables declared as register are actually auto variables.

Please take care when using register variables: While they are helpful and can lead to a tremendous speedup when used correctly, improper usage will cause bloated code and a slowdown.

9. Inline assembler

The compiler allows to insert inline assembler code in the form of the asm expression into the output file. The syntax is


        asm [optional volatile] (<string literal>[, optional parameters])


        __asm__ [optional volatile] (<string literal>[, optional parameters])

The first form is in the user namespace; and, is disabled by --standard if the argument is not cc65.

The asm expression can be used only inside a function. The result of an asm expression is always of type void.

The contents of the string literal are preparsed by the compiler; and, inserted into the generated assembly output, so that it can be processed further by the backend -- and, especially the optimizer. For that reason, the compiler does allow only regular 6502 opcodes to be used with the inline assembler. Pseudo instructions (like .import, .byte, and so on) are not allowed, even if the ca65 assembler (which is used to translate the generated assembler code) would accept them. The built-in inline assembler is not a replacement for the full-blown macro assembler which comes with the compiler.

Note: Inline assembler expressions are subject to all optimizations done by the compiler. There currently is no way to protect an inline assembler expression -- alone -- from being moved or removed completely by the optimizer. If in doubt, check the generated assembler output; or, disable optimizations (for that function).

As a shortcut, you can put the volatile qualifier in your asm expressions. It will disable optimization for the functions in which those asm volatile expressions sit. The effect is the same as though you put #pragma optimize(push, off) above those functions, and #pragma optimize(pop) below those functions.

The string literal may contain format specifiers from the following list. For each format specifier, an argument is expected which is inserted instead of the format specifier, before passing the assembly code line to the backend.

Note: The string literal as the inline assembler code itself in the asm expression is not subject to string literal translation (see #pragma charmap()) and will always be in the host encoding. On the other hand, all character and string literals as the arguments for replacing the format specifiers will be translated as usual.

%b - Numerical 8-bit value
%w - Numerical 16-bit value
%l - Numerical 32-bit value
%v - Assembler name of a global variable or function
%o - Stack offset of a local variable
%g - Assembler name of a C label
%s - The argument is converted to a string
%% - The % sign itself

Using those format specifiers, you can access C #defines, variables, or similar stuff from the inline assembler. For example, to load the value of a C #define into the Y index register, one would use


        #define OFFS  23
        __asm__ ("ldy #%b", OFFS);

Or, to access a struct member of a static variable:


        typedef struct {
            unsigned char x;
            unsigned char y;
            unsigned char color;
            unsigned char data[32];
        } pixel_t;
        static pixel_t pixel;
        __asm__ ("ldy #%b", offsetof(pixel_t, color));
        __asm__ ("lda %v,y", pixel);

        /* or to access an array member */
        static unsigned char i;
        __asm__ ("ldy %v", i);
        __asm__ ("lda %v+%b,y", pixel, offsetof(pixel_t, data));

The next example shows how to use global variables to exchange data between C and assembler; and, how to handle assembler jumps:


        static unsigned char globalSubA, globalSubB, globalSubResult;

        /* return a-b, return 255 if b>a */
        unsigned char sub (unsigned char a, unsigned char b)
        {
            globalSubA = a;
            globalSubB = b;
            __asm__ ("sec");
            __asm__ ("lda %v", globalSubA);
            __asm__ ("sbc %v", globalSubB);
            __asm__ ("bcs %g", jumpSubNoError);
            __asm__ ("lda #$FF");
        jumpSubNoError:
            __asm__ ("sta %v", globalSubResult);
            return globalSubResult;
        }

Arrays also can be accessed:


        static const unsigned char globalSquareTable[] = {
            0, 1, 4, 9, 16, 25, 36, 49, 64, 81,
            100, 121, 144, 169, 196, 225
        };
        static unsigned char globalSquareA, globalSquareResult;

        /* return a*a for a<16, else 255 */
        unsigned char square (unsigned char a)
        {
            if (a > 15) {
                return 255;
            }
            globalSquareA = a;
            __asm__ ("ldx %v", globalSquareA);
            __asm__ ("lda %v,x", globalSquareTable);
            __asm__ ("sta %v", globalSquareResult);
            return globalSquareResult;
        }

Note: Do not embed the assembler labels that are used as names of global variables or functions into your asm expressions. Code such as this:


        int foo;
        int bar (void) { return 1; }
        ...
        __asm__ ("lda _foo");           /* DON'T DO THAT! */
        ...
        __asm__ ("jsr _bar");           /* DON'T DO THAT EITHER! */

might stop working if the way that the compiler generates those names is changed in a future version. Instead, use the format specifiers from the table above:


        __asm__ ("lda %v", foo);        /* OK */
        ...
        __asm__ ("jsr %v", bar);        /* OK */

10. Implementation-defined behavior

This section describes the behavior of cc65 when the standard describes the behavior as implementation-defined.

(to be done)

11. 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 permissible 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.

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

Small parts of the compiler (parts of the preprocessor and main parser) are still covered by this copyright. The main portion is covered by the usual cc65 license, which reads:

This software is provided 'as-is', without any expressed or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.

Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:

The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
This notice may not be removed or altered from any source distribution.

cc65 Users Guide

Ullrich von Bassewitz, Greg King

Ullrich von Bassewitz,
Greg King