243 lines
4.3 KiB
HTML
243 lines
4.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>External filters</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Linux Assembly HOWTO"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Metaprogramming"
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HREF="metaprogramming.html"><LINK
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TITLE="Metaprogramming"
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TITLE="Metaprogramming"
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>Linux Assembly HOWTO</TH
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VALIGN="bottom"
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>Chapter 4. Metaprogramming</TD
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WIDTH="100%"></DIV
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><DIV
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CLASS="section"
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><H1
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CLASS="section"
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><A
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NAME="AEN576"
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></A
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>4.1. External filters</H1
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><P
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> Whatever is the macro support from your assembler, or whatever language you
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use (even C!), if the language is not expressive enough to you, you can have
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files passed through an external filter with a Makefile rule like that:
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</P
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><P
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> <TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="programlisting"
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> %.s: %.S other_dependencies
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$(FILTER) $(FILTER_OPTIONS) < $< > $@
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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</P
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><DIV
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CLASS="section"
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><H2
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CLASS="section"
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><A
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NAME="AEN581"
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></A
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>4.1.1. CPP</H2
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><P
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> CPP is truly not very expressive, but it's enough for easy things, it's
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standard, and called transparently by GCC.
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</P
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><P
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> As an example of its limitations, you can't declare objects so that destructors
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are automatically called at the end of the declaring block; you don't have
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diversions or scoping, etc.
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</P
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><P
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> CPP comes with any C compiler. However, considering how mediocre it is, stay
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away from it if by chance you can make it without C.
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</P
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></DIV
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><DIV
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CLASS="section"
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><H2
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CLASS="section"
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><A
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NAME="AEN586"
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></A
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>4.1.2. M4</H2
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><P
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> M4 gives you the full power of macroprocessing, with a Turing equivalent
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language, recursion, regular expressions, etc. You can do with it everything
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that CPP cannot.
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</P
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><P
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> See
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macro4th (this4th) as an example of advanced macroprogramming using m4.
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</P
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><P
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> However, its disfunctional quoting and unquoting semantics force you to use
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explicit continuation-passing tail-recursive macro style if you want to do
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<EM
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>advanced</EM
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> macro programming (which is remindful of TeX
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-- BTW, has anyone tried to use TeX as a macroprocessor for anything else than
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typesetting ?). This is NOT worse than CPP that does not allow quoting and
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recursion anyway.
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</P
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><P
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> The right version of M4 to get is <TT
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CLASS="literal"
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>GNU m4</TT
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> which has the most
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features and the least bugs or limitations of all. m4 is designed to be slow
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for anything but the simplest uses, which might still be ok for most assembly
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programming (you are not writing million-lines assembly programs, are you?).
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</P
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></DIV
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><DIV
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CLASS="section"
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><H2
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CLASS="section"
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><A
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NAME="AEN595"
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></A
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>4.1.3. Macroprocessing with your own filter</H2
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><P
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> You can write your own simple macro-expansion filter with the usual tools:
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perl, awk, sed, etc. It can be made rather quickly, and you control everything.
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But, of course, power in macroprocessing implies "the hard way".
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</P
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>Metaprogramming</TD
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