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revise note on prototypes/K&R conventions

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Brad Smith 2016-02-26 17:33:46 -05:00
parent fd708d30ec
commit 222ab93026
1 changed files with 11 additions and 10 deletions
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21
doc/cc65-intern.sgml
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@ -40,7 +40,11 @@ If the <tt/--standard/ command line option is used,
the <tt/cdecl/ and <tt/fastcall/ keywords will not be available.
The standard compliant variations <tt/__cdecl__/ and <tt/__fastcall__/ are always available.
K &amp; R style function prototypes may be used, but they do not alter the calling conventions in any way.
If a function has a prototype, parameters are pushed to the C-stack as their respective types
(i.e. a <tt/char/ parameter will push 1 byte), but if a function has no prototype, default
promotions will apply. This means that with no prototype, <tt/char/ will be promoted
to <tt/int/ and be pushed as 2 bytes. K &amp; R style function prototypes may be used,
but they will function the same as if no prototype was used.
<sect1>Prologue, before the function call<p>
@ -57,8 +61,9 @@ All other parameters will be pushed to the C-stack from left to right.
The rightmost parameter will have the lowest address on the stack,
and multi-byte parameters will have their least significant byte at the lower address.
The <tt/Y/ register will contain the number of bytes pushed to the stack for this function,
and the <tt/sp/ pseudo-register is a zeropage pointer to the base of the C-stack.
The <tt/sp/ pseudo-register is a zeropage pointer to the base of the C-stack.
If the function has no prototype or is variadic
the <tt/Y/ register will contain the number of bytes pushed to the stack for this function.
Example:
<tscreen><verb>
@ -84,10 +89,6 @@ void foo(unsigned bar, unsigned char baz);
lda (sp),y ; Low byte now in A
</verb></tscreen>
Variadic functions push all parameters exactly as other <tt/cdecl/ convention functions,
but the value of <tt/Y/ should be used to determine how many bytes of parameters
were placed onto the stack.
<sect1>Epilogue, after the functiona call<p>
<sect2>Return requirements</p>
@ -106,10 +107,10 @@ of <tt>A/X/sreg</tt>, so these may be clobbered by the function.
The C-stack pointer <tt/sp/ must be restored by the function to its value before the
function call prologue. It may pop all of its parameters from the C-stack
(e.g. using the <tt/runtime/ function <tt/popa/.),
(e.g. using the <tt/runtime/ function <tt/popa/),
or it could adjust <tt/sp/ directly.
On entry to the function the <tt/Y/ register contains the number of bytes
pushed to the stack, which may be added to <tt/sp/ to restore its original state.
If the function has no prototype, or is variadic the <tt/Y/ register contains the
number of bytes pushed to the stack on entry, which may be added to <tt/sp/ to restore its original state.
The internal pseudo-register <tt/regbank/ must not be changed by the function.