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Changed the documentation to reflect the new fastcall/cdecl reality.

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This commit is contained in:
Greg King
2015-03-13 05:40:55 -04:00
parent a798b1d648
commit 604a5b4447
2 changed files with 60 additions and 34 deletions
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75
doc/cc65.sgml
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@@ -3,7 +3,7 @@
<article> <article>
<title>cc65 Users Guide <title>cc65 Users Guide
<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz"> <author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">
<date>2000-09-03, 2001-10-02, 2005-08-01 <date>2015-03-13
<abstract> <abstract>
cc65 is a C compiler for 6502 targets. It supports several 6502 based home cc65 is a C compiler for 6502 targets. It supports several 6502 based home
@@ -549,9 +549,9 @@ and the one defined by the ISO standard:
be passed as parameters by value. However, struct assignment *is* be passed as parameters by value. However, struct assignment *is*
possible. possible.
<p> <p>
<item> Part of the C library is available only with fastcall calling <item> Most of the C library is available only with the fastcall calling
conventions (see below). It means that you must not mix pointers to convention (see below). It means that you must not mix pointers to
those functions with pointers to user-written, not-fastcall functions. those functions with pointers to user-written, cdecl functions.
<p> <p>
<item> The <tt/volatile/ keyword doesn't have an effect. This is not as bad <item> The <tt/volatile/ keyword doesn't have an effect. This is not as bad
as it sounds, since the 6502 has so few registers that it isn't as it sounds, since the 6502 has so few registers that it isn't
@@ -589,29 +589,54 @@ This cc65 version has some extensions to the ISO C standard.
<ref id="inline-asm" name="see there">. <ref id="inline-asm" name="see there">.
<p> <p>
<item> There is a special calling convention named "fastcall". <item> The normal calling convention -- for non-variadic functions -- is
The syntax for a function declaration using fastcall is named "fastcall". The syntax for a function declaration that
<em/explicitly/ uses fastcall is
<tscreen><verb> <tscreen><verb>
&lt;return type&gt; fastcall &lt;function name&gt; (&lt;parameter list&gt;) &lt;return type&gt; fastcall &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen> </verb></tscreen>
or or
<tscreen><verb> <tscreen><verb>
&lt;return type&gt; __fastcall__ &lt;function name&gt; (&lt;parameter list&gt;) &lt;return type&gt; __fastcall__ &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen> </verb></tscreen>
An example would be An example would be
<tscreen><verb> <tscreen><verb>
void __fastcall__ f (unsigned char c) void __fastcall__ f (unsigned char c)
</verb></tscreen> </verb></tscreen>
The first form of the fastcall keyword is in the user namespace and can The first form of the fastcall keyword is in the user namespace and can
therefore be disabled with the <tt><ref id="option--standard" therefore be disabled with the <tt><ref id="option--standard"
name="--standard"></tt> command line option. name="--standard"></tt> command line option.
For functions declared as <tt/fastcall/, the rightmost parameter is not For functions that are <tt/fastcall/, the rightmost parameter is not
pushed on the stack but left in the primary register when the function pushed on the stack but left in the primary register when the function
is called. This will reduce the cost when calling assembler functions is called. That significantly reduces the cost of calling functions.
significantly, especially when the function itself is rather small. <p>
<p>
<item> There is another calling convention named "cdecl". Variadic functions
(their prototypes have an ellipsis [<tt/.../]) always use this
convention. The syntax for a function declaration using cdecl is
<tscreen><verb>
&lt;return type&gt; cdecl &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen>
or
<tscreen><verb>
&lt;return type&gt; __cdecl__ &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen>
An example would be
<tscreen><verb>
void __cdecl__ f (unsigned char c)
</verb></tscreen>
The first form of the cdecl keyword is in the user namespace and can
therefore be disabled with the <tt><ref id="option--standard"
name="--standard"></tt> 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.
<p>
<item> There are two pseudo variables named <tt/__AX__/ and <tt/__EAX__/. <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 Both refer to the primary register that is used by the compiler to
@@ -663,7 +688,7 @@ This cc65 version has some extensions to the ISO C standard.
</verb></tscreen> </verb></tscreen>
Since the variable is of type <tt/void/ you may not use it as is. 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*/ However, taking the address of the variable results in a <tt/void */
which may be passed to any function expecting a pointer. which may be passed to any function expecting a pointer.
See the <url url="geos.html" name="GEOS library document"> for examples See the <url url="geos.html" name="GEOS library document"> for examples

19
doc/customizing.sgml
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@@ -3,7 +3,7 @@
<article> <article>
<title>Defining a Custom cc65 Target <title>Defining a Custom cc65 Target
<author>Bruce Reidenbach <author>Bruce Reidenbach
<date>2010-02-22 <date>2015-03-13
<abstract> <abstract>
This section provides step-by-step instructions on how to use the cc65 This section provides step-by-step instructions on how to use the cc65
@@ -525,15 +525,16 @@ The first step in creating the assembly language code for the driver is
to determine how to pass the C arguments to the assembly language to determine how to pass the C arguments to the assembly language
routine. The cc65 toolset allows the user to specify whether the data routine. The cc65 toolset allows the user to specify whether the data
is passed to a subroutine via the stack or by the processor registers by is passed to a subroutine via the stack or by the processor registers by
using the <tt>__fastcall__</tt> function declaration (note that there using the <tt/__fastcall__/ and <tt/__cdecl__/ function qualifiers (note that
are two underscore characters in front of and two behind the there are two underscore characters in front of and two behind each
<tt>fastcall</tt> declaration). When <tt>__fastcall__</tt> is qualifier). <tt/__fastcall__/ is the default. When <tt/__cdecl__/ <em/isn't/
specified, the rightmost argument in the function call is passed to the specified, and the function isn't variadic (i.e., its prototype doesn't have
an ellipsis), the rightmost argument in the function call is passed to the
subroutine using the 6502 registers instead of the stack. Note that if subroutine using the 6502 registers instead of the stack. Note that if
there is only one argument in the function call, the execution overhead there is only one argument in the function call, the execution overhead
required by the stack interface routines is completely avoided. required by the stack interface routines is completely avoided.
Without <tt>__fastcall__</tt>, the argument is loaded in the A and X With <tt/__cdecl__</tt>, the last argument is loaded into the A and X
registers and then pushed onto the stack via a call to <tt>pushax</tt>. registers and then pushed onto the stack via a call to <tt>pushax</tt>.
The first thing the subroutine does is retrieve the argument from the The first thing the subroutine does is retrieve the argument from the
stack via a call to <tt>ldax0sp</tt>, which copies the values into the A stack via a call to <tt>ldax0sp</tt>, which copies the values into the A
@@ -561,7 +562,7 @@ _foo: jsr ldax0sp ; Retrieve A and X from the stack
jmp incsp2 ; Pop A and X from the stack (includes return) jmp incsp2 ; Pop A and X from the stack (includes return)
</verb></tscreen> </verb></tscreen>
If <tt>__fastcall__</tt> is specified, the argument is loaded into the A If <tt/__cdecl__/ isn't specified, then the argument is loaded into the A
and X registers as before, but the subroutine is then called and X registers as before, but the subroutine is then called
immediately. The subroutine does not need to retrieve the argument immediately. The subroutine does not need to retrieve the argument
since the value is already available in the A and X registers. since the value is already available in the A and X registers.
@@ -596,7 +597,7 @@ variable which is stored in the zero page memory space in order to allow
for retrieval of each character in the string via the indirect indexed for retrieval of each character in the string via the indirect indexed
addressing mode. addressing mode.
The assembly language routine is stored in a file names The assembly language routine is stored in a file named
&quot;rs232_tx.s&quot; and is shown below: &quot;rs232_tx.s&quot; and is shown below:
<tscreen><code> <tscreen><code>
@@ -680,7 +681,7 @@ all of the behind-the-scene work is transparent to the user.
#define TX_FIFO_FULL (FIFO_STATUS &amp; 0x01) #define TX_FIFO_FULL (FIFO_STATUS &amp; 0x01)
#define RX_FIFO_EMPTY (FIFO_STATUS &amp; 0x02) #define RX_FIFO_EMPTY (FIFO_STATUS &amp; 0x02)
extern void wait (); extern void wait (void);
extern void __fastcall__ rs232_tx (char *str); extern void __fastcall__ rs232_tx (char *str);
int main () { int main () {