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><A
NAME="AEN525"
>3.9. Assembler Modes and Pragmas</A
></H1
><P
>There are a number of options that affect the way assembly is performed.
Some of these options can only be specified on the command line because
they determine something absolute about the assembly process. These include
such things as the output target. Other things may be switchable during
the assembly process. These are known as pragmas and are, by definition,
not portable between assemblers.</P
><P
>LWASM supports a number of pragmas that affect code generation or
otherwise affect the behaviour of the assembler. These may be specified by
way of a command line option or by assembler directives. The directives
are as follows.</P
><P
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><DT
>PRAGMA <CODE
CLASS="PARAMETER"
>pragma[,...]</CODE
></DT
><DD
><P
>Specifies that the assembler should bring into force all <CODE
CLASS="PARAMETER"
>pragma</CODE
>s
specified. Any unrecognized pragma will cause an assembly error. The new
pragmas will take effect immediately. This directive should be used when
the program will assemble incorrectly if the pragma is ignored or not supported.</P
></DD
><DT
>*PRAGMA <CODE
CLASS="PARAMETER"
>pragma[,...]</CODE
></DT
><DD
><P
>This is identical to the PRAGMA directive except no error will occur with
unrecognized or unsupported pragmas. This directive, by virtue of starting
with a comment character, will also be ignored by assemblers that do not
support this directive. Use this variation if the pragma is not required
for correct functioning of the code.</P
></DD
></DL
></DIV
><P
>Each pragma supported has a positive version and a negative version.
The positive version enables the pragma while the negative version disables
it. The negatitve version is simply the positive version with "no" prefixed
to it. For instance, "pragma" vs. "nopragma". Only the positive version is
listed below.</P
><P
>Pragmas are not case sensitive.</P
><P
></P
><DIV
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><DL
><DT
>index0tonone</DT
><DD
><P
>When in force, this pragma enables an optimization affecting indexed addressing
modes. When the offset expression in an indexed mode evaluates to zero but is
not explicity written as 0, this will replace the operand with the equivalent
no offset mode, thus creating slightly faster code. Because of the advantages
of this optimization, it is enabled by default.</P
></DD
><DT
>cescapes</DT
><DD
><P
>This pragma will cause strings in the FCC, FCS, and FCN pseudo operations to
have C-style escape sequences interpreted. The one departure from the official
spec is that unrecognized escape sequences will return either the character
immediately following the backslash or some undefined value. Do not rely
on the behaviour of undefined escape sequences.</P
></DD
><DT
>importundefexport</DT
><DD
><P
>This pragma is only valid for targets that support external references. When
in force, it will cause the EXPORT directive to act as IMPORT if the symbol
to be exported is not defined.  This is provided for compatibility with the
output of gcc6809 and should not be used in hand written code.  Because of
the confusion this pragma can cause, it is disabled by default.</P
></DD
><DT
>undefextern</DT
><DD
><P
>This pragma is only valid for targets that support external references. When in
force, if the assembler sees an undefined symbol on the second pass, it will
automatically define it as an external symbol. This automatic definition will
apply for the remainder of the assembly process, even if the pragma is
subsequently turned off. Because this behaviour would be potentially surprising,
this pragma defaults to off.</P
><P
>The primary use for this pragma is for projects that share a large number of
symbols between source files. In such cases, it is impractical to enumerate
all the external references in every source file. This allows the assembler
and linker to do the heavy lifting while not preventing a particular source
module from defining a local symbol of the same name as an external symbol
if it does not need the external symbol. (This pragma will not cause an
automatic external definition if there is already a locally defined symbol.)</P
><P
>This pragma will often be specified on the command line for large projects.
However, depending on the specific dynamics of the project, it may be sufficient
for one or two files to use this pragma internally.</P
></DD
><DT
>dollarlocal</DT
><DD
><P
>When set, a "$" in a symbol makes it local. When not set, "$" does not
cause a symbol to be local.  It is set by default except when using the OS9
target.</P
></DD
><DT
>dollarnotlocal</DT
><DD
><P
> This is the same as the "dollarlocal" pragma except its sense is
reversed.  That is, "dollarlocal" and "nodollarnotlocal" are equivalent and
"nodollarlocal" and "dollarnotlocal" are equivalent.  </P
></DD
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author	lost
date	Mon, 31 Aug 2009 08:30:13 +0000
parents	d5392bb5da3c
children