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Explain the new inline assembler syntax

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git-svn-id: svn://svn.cc65.org/cc65/trunk@995 b7a2c559-68d2-44c3-8de9-860c34a00d81
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cuz 2001-10-02 16:41:31 +00:00
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doc/cc65.sgml
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@ -399,22 +399,18 @@ This cc65 version has some extensions to the ISO C standard.
file. The syntax is file. The syntax is
<tscreen><verb> <tscreen><verb>
asm (&lt;string literal&gt;) ; asm (&lt;string literal&gt;[, optional parameters]) ;
</verb></tscreen> </verb></tscreen>
or or
<tscreen><verb> <tscreen><verb>
__asm__ (&lt;string literal&gt;) ; __asm__ (&lt;string literal&gt;[, optional parameters]) ;
</verb></tscreen> </verb></tscreen>
The first form is in the user namespace and is disabled if the <tt/-A/ The first form is in the user namespace and is disabled if the <tt/-A/
switch is given. switch is given.
The given string is inserted literally into the output file, and a There is a whole section covering inline assembler statements,
newline is appended. The statements in this string are not checked by <ref id="inline-asm" name="see there">.
the compiler, so be careful!
The asm statement may be used inside a function and on global file
level.
<p> <p>
<item> There is a special calling convention named "fastcall". This calling <item> There is a special calling convention named "fastcall". This calling
@ -727,6 +723,80 @@ id="pragma-staticlocals"<p>
<sect>Inline assembler<label id="inline-asm"><p>
The compiler allows to insert assembler statements into the output file. The
syntax is
<tscreen><verb>
asm (&lt;string literal&gt;[, optional parameters]) ;
</verb></tscreen>
or
<tscreen><verb>
__asm__ (&lt;string literal&gt;[, optional parameters]) ;
</verb></tscreen>
<p>
The first form is in the user namespace and is disabled by <tt><ref
id="option-A" name="-A"></tt>.
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 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,
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.
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.
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.
<itemize>
<item><tt/%b/ - Numerical 8 bit value
<item><tt/%w/ - Numerical 16 bit value
<item><tt/%l/ - Numerical 32 bit value
<item><tt/%v/ - Assembler name of a (global) variable
<item><tt/%o/ - Stack offset of a (local) variable
<item><tt/%%/ - The % sign itself
</itemize><p>
Using these 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
<tscreen><verb>
#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, color));
__asm__ ("lda %v,y", pixel);
</verb></tscreen>
<p>
<sect>Bugs/Feedback<p> <sect>Bugs/Feedback<p>
If you have problems using the compiler, if you find any bugs, or if you're If you have problems using the compiler, if you find any bugs, or if you're