<article>
<title>cc65 Users Guide
-<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">
-<date>2015-04-21
+<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">,<newline>
+<url url="mailto:gregdk@users.sf.net" name="Greg King">
<abstract>
cc65 is a C compiler for 6502 targets. It supports several 6502 based home
<!-- Begin the document -->
-
<sect>Overview<p>
cc65 was originally a C compiler for the Atari 8-bit machines written by
-O Optimize code
-Oi Optimize code, inline more code
-Or Enable register variables
- -Os Inline some known functions
+ -Os Inline some standard functions
-T Include source as comment
-V Print the compiler version number
-W warning[,...] Suppress warnings
--debug-opt name Debug optimization steps
--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
symbols in a special section in the object file.
+ <label id="option-eagerly-inline-funcs">
+ <tag><tt>--eagerly-inline-funcs</tt></tag>
+
+ Have the compiler eagerly inline these functions from the C library:
+ <itemize>
+ <item><tt/memcpy()/
+ <item><tt/memset()/
+ <item><tt/strcmp()/
+ <item><tt/strcpy()/
+ <item><tt/strlen()/
+ <item>most of the functions declared in <tt/<ctype.h>/
+ </itemize>
+
+ Note: This has two consequences:
+ <itemize>
+ <item>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 <tt/--eagerly-inline-funcs/ actually will break things.
+ <p>
+ <item>The inlined string and memory functions will not handle strings or
+ memory areas larger than 255 bytes. Similarly, the inlined <tt/is..()/
+ functions will not work with values outside the char. range (such as
+ <tt/EOF/).
+ <p>
+ </itemize>
+
+ <tt/--eagerly-inline-funcs/ implies the <tt><ref id="option-inline-stdfuncs"
+ name="--inline-stdfuncs"></tt> command line option.
+
+ See also <tt><ref id="pragma-allow-eager-inline" name="#pragma allow-eager-inline"></tt>.
+
+
<tag><tt>-h, --help</tt></tag>
Print the short option summary shown above.
+ <label id="option-inline-stdfuncs">
+ <tag><tt>--inline-stdfuncs</tt></tag>
+
+ Allow the compiler to inline some standard functions from the C library like
+ strlen. This will not only remove the overhead for a function call, but will
+ make the code visible for the optimizer. See also the <tt><ref id="option-O"
+ name="-Os"></tt> command line option and <tt><ref id="pragma-inline-stdfuncs"
+ name="#pragma inline-stdfuncs"></tt>.
+
+
<label id="option-list-warnings">
<tag><tt>--list-warnings</tt></tag>
<item>lunix
<item>lynx
<item>nes
+ <item>osic1p
<item>pet (all CBM PET systems except the 2001)
<item>plus4
<item>sim6502
<item>sim65c02
<item>supervision
+ <item>telestrat
<item>vic20
</itemize>
using
<tscreen><verb>
- void f (void)
- {
- unsigned a = 1;
- ...
- }
+ void f (void)
+ {
+ unsigned a = 1;
+ ...
+ }
</verb></tscreen>
the variable <tt/a/ will always have the value <tt/1/ when entering the
function and using <tt/-Cl/, while in
<tscreen><verb>
- void f (void)
- {
- static unsigned a = 1;
- ....
- }
+ void f (void)
+ {
+ static unsigned a = 1;
+ ....
+ }
</verb></tscreen>
the variable <tt/a/ will have the value <tt/1/ only the first time that the
name="--register-vars">/ command line option, and the <ref
id="register-vars" name="discussion of register variables"> below.
- Using <tt/-Os/ will force the compiler to inline some known functions from
- the C library like strlen. Note: This has two consequences:
- <p>
- <itemize>
- <item>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
- <tt/-Os/ will actually break things.
- <p>
- <item>The inlined string and memory functions will not handle strings or
- memory areas larger than 255 bytes. Similarly, the inlined <tt/is..()/
- functions will not work with values outside the char. range (such as
- <tt/EOF/).
- <p>
- </itemize>
- <p>
+ Using <tt/-Os/ will allow the compiler to inline some standard functions
+ from the C library like strlen. This will not only remove the overhead
+ for a function call, but will make the code visible for the optimizer.
+ See also the <tt/<ref id="option-inline-stdfuncs" name="--inline-stdfuncs">/
+ command line option.
+
It is possible to concatenate the modifiers for <tt/-O/. For example, to
- enable register variables and inlining of known functions, you may use
+ enable register variables and inlining of standard functions, you may use
<tt/-Ors/.
<label id="option-W">
- <tag><tt>-W name[,name]</tt></tag>
+ <tag><tt>-W name[,name,...]</tt></tag>
This option allows to control warnings generated by the compiler. It is
- followed by a comma separated list of warnings that should be enabled or
+ followed by a comma-separated list of warnings that should be enabled or
disabled. To disable a warning, its name is prefixed by a minus sign. If
no such prefix exists, or the name is prefixed by a plus sign, the warning
is enabled.
- The following warning names are currently recognized:
+ The following warning names currently are recognized:
<descrip>
<tag><tt/const-comparison/</tag>
Warn if the result of a comparison is constant.
Treat all warnings as errors.
<tag><tt/no-effect/</tag>
Warn about statements that don't have an effect.
+ <tag><tt/remap-zero/</tag>
+ Warn about a <tt/<ref id="pragma-charmap" name="#pragma charmap()">/
+ that changes a character's code number from/to 0x00.
<tag><tt/struct-param/</tag>
Warn when passing structs by value.
<tag><tt/unknown-pragma/</tag>
- Warn about known #pragmas.
+ Warn about #pragmas that aren't recognized by cc65.
<tag><tt/unused-label/</tag>
Warn about unused labels.
<tag><tt/unused-param/</tag>
Warn about unused variables.
</descrip>
- The full list of available warning names may be retrieved by using the
+ The full list of available warning names can be retrieved by using the
option <tt><ref id="option-list-warnings" name="--list-warnings"></tt>.
- You may also use <tt><ref id="pragma-warn" name="#pragma warn"></tt> to
- control this setting for smaller pieces of code from within your code.
+ You may use also <tt><ref id="pragma-warn" name="#pragma warn"></tt> to
+ control this setting, for smaller pieces of code, from within your sources.
</descrip><p>
+
<sect>Input and output<p>
The compiler will accept one C file per invocation and create a file with
<itemize>
-<item> The datatypes "float" and "double" are not available.
- <p>
-<item> C Functions may not return structs (or unions), and structs may not
+<item> The datatypes "float" and "double" are not available.
+<item> C Functions may not return structs (or unions), and structs may not
be passed as parameters by value. However, struct assignment *is*
- possible.
- <p>
-<item> Most of the C library is available only with the fastcall calling
+ possible.
+<item> Most of the C library is available with only the fastcall calling
convention (<ref id="extension-fastcall" name="see below">). It means
that you must not mix pointers to those functions with pointers to
- user-written, cdecl functions.
- <p>
-<item> The <tt/volatile/ keyword doesn't have an effect. This is not as bad
+ user-written, cdecl functions (the calling conventions are incompatible).
+<item> The <tt/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.
- <p>
</itemize>
There may be some more minor differences I'm currently not aware of. The
<itemize>
-<item> The compiler allows to insert assembler statements into the output
- file. The syntax is
+<item> The compiler allows to insert assembler statements into the output
+ file. The syntax is
- <tscreen><verb>
- asm (<string literal>[, optional parameters]) ;
- </verb></tscreen>
- or
- <tscreen><verb>
- __asm__ (<string literal>[, optional parameters]) ;
- </verb></tscreen>
+ <tscreen><verb>
+ asm [optional volatile] (<string literal>[, optional parameters]) ;
+ </verb></tscreen>
+ or
+ <tscreen><verb>
+ __asm__ [optional volatile] (<string literal>[, optional parameters]) ;
+ </verb></tscreen>
- The first form is in the user namespace and is disabled if the <tt/-A/
- switch is given.
+ The first form is in the user namespace; and, is disabled if the <tt/-A/
+ switch is given.
- There is a whole section covering inline assembler statements,
- <ref id="inline-asm" name="see there">.
- <p>
+ There is a whole section covering inline assembler statements,
+ <ref id="inline-asm" name="see there">.
<label id="extension-fastcall">
<item> The normal calling convention -- for non-variadic functions -- is
<tscreen><verb>
<return type> __fastcall__ <function name> (<parameter list>)
</verb></tscreen>
- An example would be
+ An example is
<tscreen><verb>
void __fastcall__ f (unsigned char c)
</verb></tscreen>
For functions that are <tt/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 functions.
- <newline><newline>
+ is called. That significantly reduces the cost of calling those functions.
<p>
<item> There is another calling convention named "cdecl". Variadic functions
<tscreen><verb>
<return type> __cdecl__ <function name> (<parameter list>)
</verb></tscreen>
- An example would be
+ An example is
<tscreen><verb>
- int * __cdecl__ f (unsigned char c)
+ int* __cdecl__ f (unsigned char c)
</verb></tscreen>
The first form of the cdecl keyword is in the user namespace;
- and therefore, can be disabled with the <tt><ref id="option--standard"
- name="--standard"></tt> command-line option.
+ and therefore, can be disabled with the <tt/<ref id="option--standard"
+ name="--standard">/ command-line option.
For functions that are <tt/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.<newline><newline>
+ places.
<p>
-<item> There are two pseudo variables named <tt/__AX__/ and <tt/__EAX__/.
- Both refer to the primary register that is used by the compiler to
- evaluate expressions or return function results. <tt/__AX__/ is of
- type <tt/unsigned int/ and <tt/__EAX__/ of type <tt/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
+<item> There are two pseudo variables named <tt/__AX__/ and <tt/__EAX__/.
+ Both refer to the primary register that is used by the compiler to
+ evaluate expressions or return function results. <tt/__AX__/ is of
+ type <tt/unsigned int/ and <tt/__EAX__/ of type <tt/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
- <tscreen><verb>
- #define hi(x) \
+ <tscreen><verb>
+ #define hi(x) \
(__AX__ = (x), \
asm ("txa"), \
asm ("ldx #$00"), \
__AX__)
- </verb></tscreen>
+ </verb></tscreen>
+
+ will give the high byte of any unsigned value.
+ <p>
- will give the high byte of any unsigned value.
- <p>
+<item> Inside a function, the identifier <tt/__func__/ gives the name of the
+ current function as a string. Outside of functions, <tt/__func__/ is
+ undefined.
+ Example:
+
+ <tscreen><verb>
+ #define PRINT_DEBUG(s) printf ("%s: %s\n", __func__, s);
+ </verb></tscreen>
-<item> Inside a function, the identifier <tt/__func__/ gives the name of the
- current function as a string. Outside of functions, <tt/__func__/ is
- undefined.
- Example:
+ The macro will print the name of the current function plus a given
+ string.
+ <p>
- <tscreen><verb>
- #define PRINT_DEBUG(s) printf ("%s: %s\n", __func__, s);
- </verb></tscreen>
+<item> cc65 allows the initialization of <tt/void/ variables. This may be
+ used to create arbitrary structures that are more compatible with
+ interfaces written for assembler languages. Here is an example:
- The macro will print the name of the current function plus a given
- string.
- <p>
+ <tscreen><verb>
+ void GCmd = { (char)3, (unsigned)0x2000, (unsigned)0x3000 };
+ </verb></tscreen>
-<item> cc65 allows the initialization of <tt/void/ variables. This may be
- used to create variable structures that are more compatible with
- interfaces written for assembler languages. Here is an example:
+ That will be translated as follows:
- <tscreen><verb>
- void GCmd = { (char)3, (unsigned)0x2000, (unsigned)0x3000 };
- </verb></tscreen>
+ <tscreen><verb>
+ _GCmd:
+ .byte 3
+ .word $2000
+ .word $3000
+ </verb></tscreen>
- This will be translated as follows:
+ Since the variable is of type <tt/void/, you may not use it as-is.
+ However, taking the address of the variable results in a <tt/void*/
+ which may be passed to any function expecting a pointer. Also, the
+ <tt/sizeof/ operator will give the length of the initializer:
- <tscreen><verb>
- _GCmd:
- .byte 3
- .word $2000
- .word $3000
- </verb></tscreen>
+ <tscreen><verb>
+ GLen = sizeof GCmd;
+ </verb></tscreen>
- Since the variable is of type <tt/void/ you may not use it as is.
- However, taking the address of the variable results in a <tt/void */
- which may be passed to any function expecting a pointer.
+ will assign the value 5 to <tt/GLen/.
- See the <url url="geos.html" name="GEOS library document"> for examples
- on how to use this feature.
- <p>
+ See the <url url="geos.html" name="GEOS library document"> for examples
+ on how to use that feature.
<item> cc65 implements flexible array struct members as defined in the C99 ISO
standard. As an extension, these fields may be initialized. There are
size zero, even if it is initialized.
<p>
+<item> 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:
+
+ <tscreen><verb>
+ static const void * const jumptable[] = {
+ &&add,
+ &&sub
+ };
+ goto *jumptable[somevar];
+
+ add:
+ ...code...
+ </verb></tscreen>
+
+ In the jump table, no expressions are supported. The array index
+ used in the goto must be a simple variable or a constant.
+
</itemize>
<p>
+
<sect>Predefined macros<p>
The compiler defines several macros at startup:
This macro is defined if the target is the enhanced Apple //e (-t apple2enh).
+ <tag><tt>__ATARI2600__</tt></tag>
+
+ This macro is defined if the target is the Atari 2600 game console.
+
<tag><tt>__ATARI5200__</tt></tag>
This macro is defined if the target is the Atari 5200 game console.
This macro expands to the date of translation of the preprocessing
translation unit in the form "Mmm dd yyyy".
+ <tag><tt>__EAGERLY_INLINE_FUNCS__</tt></tag>
+
+ Is defined if the compiler was called with the <tt><ref id="option-eagerly-inline-funcs"
+ name="--eagerly-inline-funcs"></tt> command line option.
+
<tag><tt>__FILE__</tt></tag>
This macro expands to a string containing the name of the C source file.
Is defined if the compiler was called with the <tt/-Os/ command line option.
+ <tag><tt>__OSIC1P__</tt></tag>
+
+ This macro is defined if the target is the Ohio Scientific Challenger 1P
+ (-t osic1p).
+
<tag><tt>__PET__</tt></tag>
This macro is defined if the target is the PET family of computers (-t pet).
This macro is defined if the target is the Supervision (-t supervision).
+ <tag><tt>__TELESTRAT__</tt></tag>
+
+ This macro is defined if the target is the Telestrat (-t telestrat).
+
<tag><tt>__TIME__</tt></tag>
This macro expands to the time of translation of the preprocessing
</descrip>
+
<sect>#pragmas<label id="pragmas"><p>
The compiler understands some pragmas that may be used to change code
before changing it. The value may later be restored by using the <tt/pop/
parameter with the <tt/#pragma/.
+
+<sect1><tt>#pragma allow-eager-inline ([push,] on|off)</tt><label id="pragma-allow-eager-inline"><p>
+
+ 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 <tt><ref id="option-eagerly-inline-funcs" name="--eagerly-inline-funcs"></tt>
+ command line option) this pragma does not imply the <tt><ref id="option-inline-stdfuncs"
+ name="--inline-stdfuncs"></tt> command line option. Rather it marks code to be safe for
+ eager inlining of known functions if inlining of standard functions is enabled.
+
+ The <tt/#pragma/ understands the push and pop parameters as explained above.
+
+
<sect1><tt>#pragma bss-name ([push,] <name>)</tt><label id="pragma-bss-name"><p>
This pragma changes the name used for the BSS segment (the BSS segment
Example:
<tscreen><verb>
- #pragma bss-name ("MyBSS")
+ #pragma bss-name ("MyBSS")
</verb></tscreen>
<sect1><tt>#pragma charmap (<index>, <code>)</tt><label id="pragma-charmap"><p>
Each literal string and each literal character in the source is translated
- by use of a translation table. This 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.
+ 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
- 1-255.
+ adjusted. Both arguments are assumed to be unsigned characters with a valid
+ range of 0-255.
- Beware of two pitfalls:
-
- <itemize>
- <item>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. This means that <tt/#pragma charmap/ is not
- portable -- it depends on the build environment.
- <item>While it is possible to use character literals as indices, the
- result may be somewhat unexpected, since character literals are
- itself translated. For this reason I would suggest to avoid
- character literals and use numeric character codes instead.
- </itemize>
+ Beware of some pitfalls:
+ <itemize>
+ <item>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 <tt/#pragma charmap()/ is not
+ portable -- it depends on the build environment.
+ <item>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.
+ <item>It is risky to change index <tt/0x00/, because string functions depend
+ on it. If it is changed, then the <tt/'\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 <tt/remap-zero/ warning
+ if you are certain that you know what you are doing (see <tt/<ref
+ id="pragma-warn" name="#pragma warn()">/).
+ </itemize>
Example:
<tscreen><verb>
- /* Use a space wherever an 'a' occurs in ISO-8859-1 source */
- #pragma charmap (0x61, 0x20);
+ /* Use a space wherever an 'a' occurs in ISO-8859-1 source */
+ #pragma charmap (0x61, 0x20);
</verb></tscreen>
The <tt/#pragma/ understands the push and pop parameters as explained above.
+
<sect1><tt>#pragma code-name ([push,] <name>)</tt><label id="pragma-code-name"><p>
This pragma changes the name used for the CODE segment (the CODE segment
Example:
<tscreen><verb>
- #pragma code-name ("MyCODE")
+ #pragma code-name ("MyCODE")
</verb></tscreen>
Example:
<tscreen><verb>
- #pragma data-name ("MyDATA")
+ #pragma data-name ("MyDATA")
</verb></tscreen>
+<sect1><tt>#pragma inline-stdfuncs ([push,] on|off)</tt><label id="pragma-inline-stdfuncs"><p>
+
+ 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 <tt/<ref id="option-inline-stdfuncs" name="--inline-stdfuncs">/
+ command line option.
+
+ The <tt/#pragma/ understands the push and pop parameters as explained above.
+
+
<sect1><tt>#pragma local-strings ([push,] on|off)</tt><label id="pragma-local-strings"><p>
When "on", emit string literals to the data segment when they're encountered
remembered and output as a whole when translation is finished.
+<sect1><tt>#pragma message (<message>)</tt><label id="pragma-message"><p>
+
+ This pragma is used to display informational messages at compile-time.
+
+ The message intented to be displayed must be a string literal.
+
+ Example:
+ <tscreen><verb>
+ #pragma message ("in a bottle")
+ </verb></tscreen>
+
+ Results in the compiler outputting the following to stderr:
+ <tscreen><verb>
+ example.c(42): Note: in a bottle
+ </verb></tscreen>
+
+
<sect1><tt>#pragma optimize ([push,] on|off)</tt><label id="pragma-optimize"><p>
Switch optimization on or off. If the argument is "off", optimization is
Example:
<tscreen><verb>
- #pragma rodata-name ("MyRODATA")
+ #pragma rodata-name ("MyRODATA")
</verb></tscreen>
Example:
<tscreen><verb>
- #pragma regvaraddr(on) /* Allow taking the address
- * of register variables
- */
+ #pragma regvaraddr(on) /* Allow taking the address
+ * of register variables
+ */
</verb></tscreen>
Switch compiler warnings on or off. "name" is the name of a warning (see the
<tt/<ref name="-W" id="option-W">/ compiler option for a list). The name is
- either followed by "pop", which restores the last pushed state, or by "on" or
+ followed either by "pop", which restores the last pushed state, or by "on" or
"off", optionally preceeded by "push" to push the current state before
changing it.
Example:
<tscreen><verb>
/* Don't warn about the unused parameter in function func */
- #pragma warn (unused-param, push, off)
+ #pragma warn (unused-param, push, off)
static int func (int unused)
{
return 0;
#pragma warn (unused-param, pop)
</verb></tscreen>
+
+<sect1><tt>#pragma wrapped-call (push, <name>, <identifier>)</tt><label id="pragma-wrapped-call"><p>
+
+ This pragma sets a wrapper for functions, often used for trampolines.
+
+ The name is a function returning <tt/void/, and taking no parameters.
+ It must preserve the CPU's <tt/A/ and <tt/X/ registers if it wraps any
+ <tt/__fastcall__/ functions that have parameters. It must preserve
+ the <tt/Y/ register if it wraps any variadic functions (they have "<tt/.../"
+ in their prototypes).
+
+ The identifier is an 8-bit number that's set into <tt/tmp4/.
+
+ The address of a wrapped function is passed in <tt/ptr4/. The wrapper can
+ call that function by using "<tt/jsr callptr4/".
+
+ 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 <tt/#pragma/ requires the push or pop argument as explained above.
+
+ Example:
+ <tscreen><verb>
+/* 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)
+ </verb></tscreen>
+
+
<sect1><tt>#pragma writable-strings ([push,] on|off)</tt><label id="pragma-writable-strings"><p>
Changes the storage location of string literals. For historical reasons,
Example:
<tscreen><verb>
- extern int foo;
- #pragma zpsym ("foo"); /* foo is in the zeropage */
+ extern int foo;
+ #pragma zpsym ("foo"); /* foo is in the zeropage */
</verb></tscreen>
-
<sect>Register variables<label id="register-vars"><p>
The runtime for all supported platforms has 6 bytes of zero page space
syntax is
<tscreen><verb>
- asm (<string literal>[, optional parameters]) ;
+ asm [optional volatile] (<string literal>[, optional parameters]) ;
</verb></tscreen>
or
<tscreen><verb>
- __asm__ (<string literal>[, optional parameters]) ;
+ __asm__ [optional volatile] (<string literal>[, optional parameters]) ;
</verb></tscreen>
<p>
-The first form is in the user namespace and is disabled by <tt><ref
+The first form is in the user namespace; and, is disabled by <tt><ref
id="option--standard" name="--standard"></tt> if the argument is not <tt/cc65/.
-The asm statement may be used inside a function and on global file level. An
-inline assembler statement is a primary expression, so it may also be used as
-part of an expression. Please note however that the result of an expression
-containing just an inline assembler statement is always of type <tt/void/.
+The <tt/asm/ statement can be used only inside a function. Please note that
+the result of an inline assembler expression is always of type <tt/void/.
-The contents of the string literal are preparsed by the compiler and inserted
-into the generated assembly output, so that the can be further processed by
-the backend and especially the optimizer. For this reason, the compiler does
-only allow regular 6502 opcodes to be used with the inline assembler. Pseudo
-instructions (like <tt/.import/, <tt/.byte/ and so on) are <em/not/ allowed,
+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 <tt/.import/, <tt/.byte/, and so on) are <em/not/ allowed,
even if the ca65 assembler (which is used to translate the generated assembler
-code) would accept them. The builtin inline assembler is not a replacement for
-the full blown macro assembler which comes with the compiler.
+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 statements are subject to all optimizations done by the
-compiler. There is currently no way to protect an inline assembler statement
-from being moved or removed completely by the optimizer. If in doubt, check
-the generated assembler output, or disable optimizations.
+compiler. There currently is no way to protect an inline assembler statement
+-- 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 <tt/volatile/ qualifier in your <tt/asm/
+statements. It will disable optimization for the functions in which those
+<tt/asm volatile/ statements sit. The effect is the same as though you put
+<tt/#pragma optimize(push, off)/ above those functions, and <tt/#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.
+the format specifier, before passing the assembly code line to the backend.
<itemize>
<item><tt/%b/ - Numerical 8-bit value
<item><tt/%%/ - The % sign itself
</itemize><p>
-Using these format specifiers, you can access C <tt/#defines/, variables or
+Using those format specifiers, you can access C <tt/#defines/, variables, or
similar stuff from the inline assembler. For example, to load the value of
-a C <tt/#define/ into the Y register, one would use
+a C <tt/#define/ into the Y index register, one would use
<tscreen><verb>
- #define OFFS 23
- __asm__ ("ldy #%b", OFFS);
+ #define OFFS 23
+ __asm__ ("ldy #%b", OFFS);
</verb></tscreen>
Or, to access a struct member of a static variable:
<tscreen><verb>
- typedef struct {
- unsigned char x;
- unsigned char y;
- unsigned char color;
- } pixel_t;
- static pixel_t pixel;
- __asm__ ("ldy #%b", offsetof(pixel_t, color));
- __asm__ ("lda %v,y", pixel);
+ typedef struct {
+ unsigned char x;
+ unsigned char y;
+ unsigned char color;
+ } pixel_t;
+ static pixel_t pixel;
+ __asm__ ("ldy #%b", offsetof(pixel_t, color));
+ __asm__ ("lda %v,y", pixel);
</verb></tscreen>
<p>
The next example shows how to use global variables to exchange data between C
-an assembler and how to handle assembler jumps:
+and assembler; and, how to handle assembler jumps:
<tscreen><verb>
- unsigned char globalSubA, globalSubB, globalSubResult;
+ static unsigned char globalSubA, globalSubB, globalSubResult;
/* return a-b, return 255 if b>a */
unsigned char sub (unsigned char a, unsigned char b)
</verb></tscreen>
<p>
-Arrays can also be accessed:
+Arrays also can be accessed:
<tscreen><verb>
- unsigned char globalSquareTable[] = {
+ static const unsigned char globalSquareTable[] = {
0, 1, 4, 9, 16, 25, 36, 49, 64, 81,
100, 121, 144, 169, 196, 225
};
- unsigned char globalSquareA, globalSquareResult;
+ static unsigned char globalSquareA, globalSquareResult;
/* return a*a for a<16, else 255 */
unsigned char square (unsigned char a)
{
- if (a>15){
+ if (a > 15) {
return 255;
}
globalSquareA = a;
<p>
Note: Do not embed the assembler labels that are used as names of global
-variables or functions into your asm statements. Code like this
+variables or functions into your <tt/asm/ statements. Code such as this:
<tscreen><verb>
int foo;
- int bar () { return 1; }
- __asm__ ("lda _foo"); /* DON'T DO THAT! */
+ int bar (void) { return 1; }
+ ...
+ __asm__ ("lda _foo"); /* DON'T DO THAT! */
...
__asm__ ("jsr _bar"); /* DON'T DO THAT EITHER! */
</verb></tscreen>
<p>
-may stop working if the way, the compiler generates these names is changed in
-a future version. Instead use the format specifiers from the table above:
+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:
<tscreen><verb>
- __asm__ ("lda %v", foo); /* OK */
+ __asm__ ("lda %v", foo); /* OK */
...
__asm__ ("jsr %v", bar); /* OK */
</verb></tscreen>
<p>
+
<sect>Implementation-defined behavior<p>
This section describes the behavior of cc65 when the standard describes the
freely, subject to the following restrictions:
<enum>
-<item> 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.
-<item> Altered source versions must be plainly marked as such, and must not
- be misrepresented as being the original software.
-<item> This notice may not be removed or altered from any source
- distribution.
+<item> 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.
+<item> Altered source versions must be plainly marked as such, and must not
+ be misrepresented as being the original software.
+<item> This notice may not be removed or altered from any source
+ distribution.
</enum>
</article>
-
projects / cc65 / blobdiff