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value) is now gone, attributes are used instead. The SYMBOLS section does now support imports, so the linker config can be used to force symbols (and therefore module) imports. Evaluation of start address and size for memory areas has been delayed even further, so it is now possible to use the values from one memory area in the definition of the next one. git-svn-id: svn://svn.cc65.org/cc65/trunk@4851 b7a2c559-68d2-44c3-8de9-860c34a00d81
1081 lines
40 KiB
Plaintext
1081 lines
40 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>ld65 Users Guide
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<author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
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<date>02.12.2000, 02.10.2001
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<abstract>
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The ld65 linker combines object files into an executable file. ld65 is highly
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configurable and uses configuration files for high flexibility.
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</abstract>
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<!-- Table of contents -->
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<toc>
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<!-- Begin the document -->
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<sect>Overview<p>
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The ld65 linker combines several object modules created by the ca65
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assembler, producing an executable file. The object modules may be read
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from a library created by the ar65 archiver (this is somewhat faster and
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more convenient). The linker was designed to be as flexible as possible.
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It complements the features that are built into the ca65 macroassembler:
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<itemize>
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<item> Accept any number of segments to form an executable module.
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<item> Resolve arbitrary expressions stored in the object files.
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<item> In case of errors, use the meta information stored in the object files
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to produce helpful error messages. In case of undefined symbols,
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expression range errors, or symbol type mismatches, ld65 is able to
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tell you the exact location in the original assembler source, where
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the symbol was referenced.
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<item> Flexible output. The output of ld65 is highly configurable by a config
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file. More common platforms are supported by builtin configurations
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that may be activated by naming the target system. The output
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generation was designed with different output formats in mind, so
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adding other formats shouldn't be a great problem.
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</itemize>
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<sect>Usage<p>
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<sect1>Command line option overview<p>
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The linker is called as follows:
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<tscreen><verb>
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---------------------------------------------------------------------------
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Usage: ld65 [options] module ...
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Short options:
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-( Start a library group
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-) End a library group
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-C name Use linker config file
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-D sym=val Define a symbol
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-L path Specify a library search path
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-Ln name Create a VICE label file
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-S addr Set the default start address
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-V Print the linker version
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-h Help (this text)
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-m name Create a map file
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-o name Name the default output file
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-t sys Set the target system
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-u sym Force an import of symbol `sym'
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-v Verbose mode
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-vm Verbose map file
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Long options:
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--cfg-path path Specify a config file search path
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--config name Use linker config file
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--dbgfile name Generate debug information
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--define sym=val Define a symbol
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--dump-config name Dump a builtin configuration
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--end-group End a library group
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--force-import sym Force an import of symbol `sym'
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--help Help (this text)
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--lib file Link this library
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--lib-path path Specify a library search path
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--mapfile name Create a map file
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--module-id id Specify a module id
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--obj file Link this object file
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--obj-path path Specify an object file search path
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--start-addr addr Set the default start address
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--start-group Start a library group
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--target sys Set the target system
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--version Print the linker version
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---------------------------------------------------------------------------
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</verb></tscreen>
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<sect1>Command line options in detail<p>
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Here is a description of all the command line options:
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<descrip>
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<label id="option--start-group">
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<tag><tt>-(, --start-group</tt></tag>
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Start a library group. The libraries specified within a group are searched
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multiple times to resolve crossreferences within the libraries. Normally,
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crossreferences are only resolved within a library, that is the library is
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searched multiple times. Libraries specified later on the command line
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cannot reference otherwise unreferenced symbols in libraries specified
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earlier, because the linker has already handled them. Library groups are
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a solution for this problem, because the linker will search repeatedly
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through all libraries specified in the group, until all possible open
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symbol references have been satisfied.
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<tag><tt>-), --end-group</tt></tag>
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End a library group. See the explanation of the <tt><ref
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id="option--start-group" name="--start-group"></tt> option.
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<tag><tt>-h, --help</tt></tag>
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Print the short option summary shown above.
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<label id="option-m">
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<tag><tt>-m name, --mapfile name</tt></tag>
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This option (which needs an argument that will used as a filename for
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the generated map file) will cause the linker to generate a map file.
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The map file does contain a detailed overview over the modules used, the
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sizes for the different segments, and a table containing exported
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symbols.
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<label id="option-o">
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<tag><tt>-o name</tt></tag>
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The -o switch is used to give the name of the default output file.
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Depending on your output configuration, this name may NOT be used as
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name for the output file. However, for the builtin configurations, this
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name is used for the output file name.
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<label id="option-t">
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<tag><tt>-t sys, --target sys</tt></tag>
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The argument for the -t switch is the name of the target system. Since this
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switch will activate a builtin configuration, it may not be used together
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with the <tt><ref id="option-C" name="-C"></tt> option. The following target
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systems are currently supported:
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<itemize>
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<item>none
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<item>apple2
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<item>apple2enh
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<item>atari
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<item>atmos
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<item>c16 (works also for the c116 with memory up to 32K)
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<item>c64
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<item>c128
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<item>plus4
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<item>cbm510 (CBM-II series with 40 column video)
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<item>cbm610 (all CBM series-II computers with 80 column video)
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<item>pet (all CBM PET systems except the 2001)
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<item>geos
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<item>lunix
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<item>atmos
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<item>nes
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<item>supervision
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</itemize>
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There are a few more targets defined but neither of them is actually
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supported.
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<tag><tt>-u sym[:addrsize], --force-import sym[:addrsize]</tt></tag>
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Force an import of a symbol. While object files are always linked to the
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output file, regardless if there are any references, object modules from
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libraries get only linked in if an import can be satisfied by this module.
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The <tt/--fore-import/ option may be used to add a reference to a symbol and
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as a result force linkage of the module that exports the identifier.
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The name of the symbol may optionally be followed by a colon and an address
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size specifier. If no address size is specified, the default address size
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for the target machine is used.
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Please note that the symbol name needs to have the internal representation,
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meaning you have to prepend an underline for C identifiers.
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<label id="option-v">
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<tag><tt>-v, --verbose</tt></tag>
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Using the -v option, you may enable more output that may help you to
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locate problems. If an undefined symbol is encountered, -v causes the
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linker to print a detailed list of the references (that is, source file
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and line) for this symbol.
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<tag><tt>-vm</tt></tag>
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Must be used in conjunction with <tt><ref id="option-m" name="-m"></tt>
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(generate map file). Normally the map file will not include empty segments
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and sections, or unreferenced symbols. Using this option, you can force the
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linker to include all this information into the map file.
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<label id="option-C">
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<tag><tt>-C</tt></tag>
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This gives the name of an output config file to use. See section 4 for more
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information about config files. -C may not be used together with <tt><ref
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id="option-t" name="-t"></tt>.
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<label id="option-D">
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<tag><tt>-D sym=value, --define sym=value</tt></tag>
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This option allows to define an external symbol on the command line. Value
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may start with a '$' sign or with <tt/0x/ for hexadecimal values,
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otherwise a leading zero denotes octal values. See also the <ref
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id="SYMBOLS" name="SYMBOLS section"> in the configuration file.
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<label id="option--lib-path">
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<tag><tt>-L path, --lib-path path</tt></tag>
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Specify a library search path. This option may be used more than once. It
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adds a directory to the search path for library files. Libraries specified
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without a path are searched in current directory, in the directory given in
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the <tt/LD65_LIB/ environment variable, and in the list of directories
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specified using <tt/--lib-path/.
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<tag><tt>-Ln</tt></tag>
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This option allows you to create a file that contains all global labels and
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may be loaded into VICE emulator using the <tt/ll/ (load label) command. You
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may use this to debug your code with VICE. Note: Older versions had some
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bugs in the label code. If you have problems, please get the latest VICE
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version.
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<label id="option-S">
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<tag><tt>-S addr, --start-addr addr</tt></tag>
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Using -S you may define the default starting address. If and how this
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address is used depends on the config file in use. For the builtin
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configurations, only the "none", "apple2" and "apple2enh" systems honor an
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explicit start address, all other builtin config provide their own.
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<tag><tt>-V, --version</tt></tag>
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This option print the version number of the linker. If you send any
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suggestions or bugfixes, please include this number.
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<label id="option--cfg-path">
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<tag><tt>--cfg-path path</tt></tag>
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Specify a config file search path. This option may be used more than once.
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It adds a directory to the search path for config files. A config file given
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with the <tt><ref id="option-C" name="-C"></tt> option that has no path in
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its name is searched in the current directory, in the directory given in the
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<tt/LD65_CFG/ environment variable, and in the list of directories specified
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using <tt/--cfg-path/.
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<label id="option--dbgfile">
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<tag><tt>--dbgfile name</tt></tag>
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Specify an output file for debug information. Available information will be
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written to this file. Using the <tt/-g/ option for the compiler and assembler
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will increase the amount of information available. Please note that debug
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information generation is currently being developed, so the format of the
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file and it's contents are subject to change without further notice.
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<tag><tt>--lib file</tt></tag>
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Links a library to the output. Use this command line option instead of just
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naming the library file, if the linker is not able to determine the file
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type because of an unusual extension.
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<tag><tt>--obj file</tt></tag>
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Links an object file to the output. Use this command line option instead
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of just naming the object file, if the linker is not able to determine the
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file type because of an unusual extension.
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<label id="option--obj-path">
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<tag><tt>--obj-path path</tt></tag>
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Specify an object file search path. This option may be used more than once.
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It adds a directory to the search path for object files. An object file
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passed to the linker that has no path in its name is searched in current
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directory, in the directory given in the <tt/LD65_OBJ/ environment variable,
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and in the list of directories specified using <tt/--obj-path/.
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</descrip>
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<sect>Search paths<p>
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Starting with version 2.10 there are now several search paths for files needed
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by the linker: One for libraries, one for object files and one for config
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files.
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<sect1>Library search path<p>
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The library search path contains in this order:
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<enum>
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<item>The current directory.
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<item>A compiled in library path which is often <tt>/usr/lib/cc65/lib</tt> on
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Linux systems.
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<item>The value of the environment variable <tt/LD65_LIB/ if it is defined.
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<item>A subdirectory named <tt/lib/ of the directory defined in the environment
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variable <tt/CC65_HOME/, if it is defined.
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<item>Any directory added with the <tt><ref id="option--lib-path"
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name="--lib-path"></tt> option on the command line.
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</enum>
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<sect1>Object file search path<p>
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The object file search path contains in this order:
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<enum>
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<item>The current directory.
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<item>A compiled in directory which is often <tt>/usr/lib/cc65/obj</tt> on
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Linux systems.
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<item>The value of the environment variable <tt/LD65_OBJ/ if it is defined.
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<item>A subdirectory named <tt/obj/ of the directory defined in the environment
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variable <tt/CC65_HOME/, if it is defined.
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<item>Any directory added with the <tt><ref id="option--obj-path"
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name="--obj-path"></tt> option on the command line.
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</enum>
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<sect1>Config file search path<p>
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The config file search path contains in this order:
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<enum>
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<item>The current directory.
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<item>A compiled in directory which is often <tt>/usr/lib/cc65/cfg</tt> on
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Linux systems.
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<item>The value of the environment variable <tt/LD65_CFG/ if it is defined.
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<item>A subdirectory named <tt/cfg/ of the directory defined in the environment
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variable <tt/CC65_HOME/, if it is defined.
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<item>Any directory added with the <tt><ref id="option--cfg-path"
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name="--cfg-path"></tt> option on the command line.
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</enum>
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<sect>Detailed workings<p>
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The linker does several things when combining object modules:
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First, the command line is parsed from left to right. For each object file
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encountered (object files are recognized by a magic word in the header, so
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the linker does not care about the name), imported and exported
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identifiers are read from the file and inserted in a table. If a library
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name is given (libraries are also recognized by a magic word, there are no
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special naming conventions), all modules in the library are checked if an
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export from this module would satisfy an import from other modules. All
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modules where this is the case are marked. If duplicate identifiers are
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found, the linker issues a warning.
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This procedure (parsing and reading from left to right) does mean, that a
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library may only satisfy references for object modules (given directly or from
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a library) named <em/before/ that library. With the command line
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<tscreen><verb>
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ld65 crt0.o clib.lib test.o
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</verb></tscreen>
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the module test.o may not contain references to modules in the library
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clib.lib. If this is the case, you have to change the order of the modules
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on the command line:
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<tscreen><verb>
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ld65 crt0.o test.o clib.lib
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</verb></tscreen>
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Step two is, to read the configuration file, and assign start addresses
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for the segments and define any linker symbols (see <ref id="config-files"
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name="Configuration files">).
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After that, the linker is ready to produce an output file. Before doing that,
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it checks it's data for consistency. That is, it checks for unresolved
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externals (if the output format is not relocatable) and for symbol type
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mismatches (for example a zero page symbol is imported by a module as absolute
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symbol).
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Step four is, to write the actual target files. In this step, the linker will
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resolve any expressions contained in the segment data. Circular references are
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also detected in this step (a symbol may have a circular reference that goes
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unnoticed if the symbol is not used).
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Step five is to output a map file with a detailed list of all modules,
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segments and symbols encountered.
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And, last step, if you give the <tt><ref id="option-v" name="-v"></tt> switch
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twice, you get a dump of the segment data. However, this may be quite
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unreadable if you're not a developer:-)
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<sect>Configuration files<label id="config-files"><p>
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Configuration files are used to describe the layout of the output file(s). Two
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major topics are covered in a config file: The memory layout of the target
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architecture, and the assignment of segments to memory areas. In addition,
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several other attributes may be specified.
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Case is ignored for keywords, that is, section or attribute names, but it is
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<em/not/ ignored for names and strings.
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<sect1>Memory areas<p>
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Memory areas are specified in a <tt/MEMORY/ section. Lets have a look at an
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example (this one describes the usable memory layout of the C64):
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<tscreen><verb>
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MEMORY {
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RAM1: start = $0800, size = $9800;
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ROM1: start = $A000, size = $2000;
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RAM2: start = $C000, size = $1000;
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ROM2: start = $E000, size = $2000;
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}
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</verb></tscreen>
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As you can see, there are two ram areas and two rom areas. The names
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(before the colon) are arbitrary names that must start with a letter, with
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the remaining characters being letters or digits. The names of the memory
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areas are used when assigning segments. As mentioned above, case is
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significant for these names.
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The syntax above is used in all sections of the config file. The name
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(<tt/ROM1/ etc.) is said to be an identifier, the remaining tokens up to the
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semicolon specify attributes for this identifier. You may use the equal sign
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to assign values to attributes, and you may use a comma to separate
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attributes, you may also leave both out. But you <em/must/ use a semicolon to
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mark the end of the attributes for one identifier. The section above may also
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have looked like this:
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<tscreen><verb>
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# Start of memory section
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MEMORY
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{
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RAM1:
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start $0800
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size $9800;
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ROM1:
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start $A000
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size $2000;
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RAM2:
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start $C000
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size $1000;
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ROM2:
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start $E000
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size $2000;
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}
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</verb></tscreen>
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There are of course more attributes for a memory section than just start and
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size. Start and size are mandatory attributes, that means, each memory area
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defined <em/must/ have these attributes given (the linker will check that). I
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will cover other attributes later. As you may have noticed, I've used a
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comment in the example above. Comments start with a hash mark (`#'), the
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remainder of the line is ignored if this character is found.
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<sect1>Segments<p>
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Let's assume you have written a program for your trusty old C64, and you would
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like to run it. For testing purposes, it should run in the <tt/RAM/ area. So
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we will start to assign segments to memory sections in the <tt/SEGMENTS/
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section:
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<tscreen><verb>
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SEGMENTS {
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CODE: load = RAM1, type = ro;
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RODATA: load = RAM1, type = ro;
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DATA: load = RAM1, type = rw;
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BSS: load = RAM1, type = bss, define = yes;
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}
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</verb></tscreen>
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|
|
What we are doing here is telling the linker, that all segments go into the
|
|
<tt/RAM1/ memory area in the order specified in the <tt/SEGMENTS/ section. So
|
|
the linker will first write the <tt/CODE/ segment, then the <tt/RODATA/
|
|
segment, then the <tt/DATA/ segment - but it will not write the <tt/BSS/
|
|
segment. Why? Enter the segment type: For each segment specified, you may also
|
|
specify a segment attribute. There are four possible segment attributes:
|
|
|
|
<tscreen><verb>
|
|
ro means readonly
|
|
rw means read/write
|
|
bss means that this is an uninitialized segment
|
|
zp a zeropage segment
|
|
</verb></tscreen>
|
|
|
|
So, because we specified that the segment with the name BSS is of type bss,
|
|
the linker knows that this is uninitialized data, and will not write it to an
|
|
output file. This is an important point: For the assembler, the <tt/BSS/
|
|
segment has no special meaning. You specify, which segments have the bss
|
|
attribute when linking. This approach is much more flexible than having one
|
|
fixed bss segment, and is a result of the design decision to supporting an
|
|
arbitrary segment count.
|
|
|
|
If you specify "<tt/type = bss/" for a segment, the linker will make sure that
|
|
this segment does only contain uninitialized data (that is, zeroes), and issue
|
|
a warning if this is not the case.
|
|
|
|
For a <tt/bss/ type segment to be useful, it must be cleared somehow by your
|
|
program (this happens usually in the startup code - for example the startup
|
|
code for cc65 generated programs takes care about that). But how does your
|
|
code know, where the segment starts, and how big it is? The linker is able to
|
|
give that information, but you must request it. This is, what we're doing with
|
|
the "<tt/define = yes/" attribute in the <tt/BSS/ definitions. For each
|
|
segment, where this attribute is true, the linker will export three symbols.
|
|
|
|
<tscreen><verb>
|
|
__NAME_LOAD__ This is set to the address where the
|
|
segment is loaded.
|
|
__NAME_RUN__ This is set to the run address of the
|
|
segment. We will cover run addresses
|
|
later.
|
|
__NAME_SIZE__ This is set to the segment size.
|
|
</verb></tscreen>
|
|
|
|
Replace <tt/NAME/ by the name of the segment, in the example above, this would
|
|
be <tt/BSS/. These symbols may be accessed by your code.
|
|
|
|
Now, as we've configured the linker to write the first three segments and
|
|
create symbols for the last one, there's only one question left: Where does
|
|
the linker put the data? It would be very convenient to have the data in a
|
|
file, wouldn't it?
|
|
|
|
<sect1>Output files<p>
|
|
|
|
We don't have any files specified above, and indeed, this is not needed in a
|
|
simple configuration like the one above. There is an additional attribute
|
|
"file" that may be specified for a memory area, that gives a file name to
|
|
write the area data into. If there is no file name given, the linker will
|
|
assign the default file name. This is "a.out" or the one given with the
|
|
<tt><ref id="option-o" name="-o"></tt> option on the command line. Since the
|
|
default behaviour is ok for our purposes, I did not use the attribute in the
|
|
example above. Let's have a look at it now.
|
|
|
|
The "file" attribute (the keyword may also be written as "FILE" if you like
|
|
that better) takes a string enclosed in double quotes (`"') that specifies the
|
|
file, where the data is written. You may specify the same file several times,
|
|
in that case the data for all memory areas having this file name is written
|
|
into this file, in the order of the memory areas defined in the <tt/MEMORY/
|
|
section. Let's specify some file names in the <tt/MEMORY/ section used above:
|
|
|
|
<tscreen><verb>
|
|
MEMORY {
|
|
RAM1: start = $0800, size = $9800, file = %O;
|
|
ROM1: start = $A000, size = $2000, file = "rom1.bin";
|
|
RAM2: start = $C000, size = $1000, file = %O;
|
|
ROM2: start = $E000, size = $2000, file = "rom2.bin";
|
|
}
|
|
</verb></tscreen>
|
|
|
|
The <tt/%O/ used here is a way to specify the default behaviour explicitly:
|
|
<tt/%O/ is replaced by a string (including the quotes) that contains the
|
|
default output name, that is, "a.out" or the name specified with the <tt><ref
|
|
id="option-o" name="-o"></tt> option on the command line. Into this file, the
|
|
linker will first write any segments that go into <tt/RAM1/, and will append
|
|
then the segments for <tt/RAM2/, because the memory areas are given in this
|
|
order. So, for the RAM areas, nothing has really changed.
|
|
|
|
We've not used the ROM areas, but we will do that below, so we give the file
|
|
names here. Segments that go into <tt/ROM1/ will be written to a file named
|
|
"rom1.bin", and segments that go into <tt/ROM2/ will be written to a file
|
|
named "rom2.bin". The name given on the command line is ignored in both cases.
|
|
|
|
Assigning an empty file name for a memory area will discard the data written
|
|
to it. This is useful, if the a memory area has segments assigned that are
|
|
empty (for example because they are of type bss). In that case, the linker
|
|
will create an empty output file. This may be suppressed by assigning an empty
|
|
file name to that memory area.
|
|
|
|
The <tt/%O/ sequence is also allowed inside a string. So using
|
|
|
|
<tscreen><verb>
|
|
MEMORY {
|
|
ROM1: start = $A000, size = $2000, file = "%O-1.bin";
|
|
ROM2: start = $E000, size = $2000, file = "%O-2.bin";
|
|
}
|
|
</verb></tscreen>
|
|
|
|
would write two files that start with the name of the output file specified on
|
|
the command line, with "-1.bin" and "-2.bin" appended respectively. Because
|
|
'%' is used as an escape char, the sequence "%%" has to be used if a single
|
|
percent sign is required.
|
|
|
|
<sect1>LOAD and RUN addresses (ROMable code)<p>
|
|
|
|
Let us look now at a more complex example. Say, you've successfully tested
|
|
your new "Super Operating System" (SOS for short) for the C64, and you
|
|
will now go and replace the ROMs by your own code. When doing that, you
|
|
face a new problem: If the code runs in RAM, we need not to care about
|
|
read/write data. But now, if the code is in ROM, we must care about it.
|
|
Remember the default segments (you may of course specify your own):
|
|
|
|
<tscreen><verb>
|
|
CODE read only code
|
|
RODATA read only data
|
|
DATA read/write data
|
|
BSS uninitialized data, read/write
|
|
</verb></tscreen>
|
|
|
|
Since <tt/BSS/ is not initialized, we must not care about it now, but what
|
|
about <tt/DATA/? <tt/DATA/ contains initialized data, that is, data that was
|
|
explicitly assigned a value. And your program will rely on these values on
|
|
startup. Since there's no other way to remember the contents of the data
|
|
segment, than storing it into one of the ROMs, we have to put it there. But
|
|
unfortunately, ROM is not writable, so we have to copy it into RAM before
|
|
running the actual code.
|
|
|
|
The linker cannot help you copying the data from ROM into RAM (this must be
|
|
done by the startup code of your program), but it has some features that will
|
|
help you in this process.
|
|
|
|
First, you may not only specify a "<tt/load/" attribute for a segment, but
|
|
also a "<tt/run/" attribute. The "<tt/load/" attribute is mandatory, and, if
|
|
you don't specify a "<tt/run/" attribute, the linker assumes that load area
|
|
and run area are the same. We will use this feature for our data area:
|
|
|
|
<tscreen><verb>
|
|
SEGMENTS {
|
|
CODE: load = ROM1, type = ro;
|
|
RODATA: load = ROM2, type = ro;
|
|
DATA: load = ROM2, run = RAM2, type = rw, define = yes;
|
|
BSS: load = RAM2, type = bss, define = yes;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
Let's have a closer look at this <tt/SEGMENTS/ section. We specify that the
|
|
<tt/CODE/ segment goes into <tt/ROM1/ (the one at $A000). The readonly data
|
|
goes into <tt/ROM2/. Read/write data will be loaded into <tt/ROM2/ but is run
|
|
in <tt/RAM2/. That means that all references to labels in the <tt/DATA/
|
|
segment are relocated to be in <tt/RAM2/, but the segment is written to
|
|
<tt/ROM2/. All your startup code has to do is, to copy the data from it's
|
|
location in <tt/ROM2/ to the final location in <tt/RAM2/.
|
|
|
|
So, how do you know, where the data is located? This is the second point,
|
|
where you get help from the linker. Remember the "<tt/define/" attribute?
|
|
Since we have set this attribute to true, the linker will define three
|
|
external symbols for the data segment that may be accessed from your code:
|
|
|
|
<tscreen><verb>
|
|
__DATA_LOAD__ This is set to the address where the segment
|
|
is loaded, in this case, it is an address in
|
|
ROM2.
|
|
__DATA_RUN__ This is set to the run address of the segment,
|
|
in this case, it is an address in RAM2.
|
|
__DATA_SIZE__ This is set to the segment size.
|
|
</verb></tscreen>
|
|
|
|
So, what your startup code must do, is to copy <tt/__DATA_SIZE__/ bytes from
|
|
<tt/__DATA_LOAD__/ to <tt/__DATA_RUN__/ before any other routines are called.
|
|
All references to labels in the <tt/DATA/ segment are relocated to <tt/RAM2/
|
|
by the linker, so things will work properly.
|
|
|
|
|
|
<sect1>Other MEMORY area attributes<p>
|
|
|
|
There are some other attributes not covered above. Before starting the
|
|
reference section, I will discuss the remaining things here.
|
|
|
|
You may request symbols definitions also for memory areas. This may be
|
|
useful for things like a software stack, or an i/o area.
|
|
|
|
<tscreen><verb>
|
|
MEMORY {
|
|
STACK: start = $C000, size = $1000, define = yes;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
This will define three external symbols that may be used in your code:
|
|
|
|
<tscreen><verb>
|
|
__STACK_START__ This is set to the start of the memory
|
|
area, $C000 in this example.
|
|
__STACK_SIZE__ The size of the area, here $1000.
|
|
__STACK_LAST__ This is NOT the same as START+SIZE.
|
|
Instead, it it defined as the first
|
|
address that is not used by data. If we
|
|
don't define any segments for this area,
|
|
the value will be the same as START.
|
|
</verb></tscreen>
|
|
|
|
A memory section may also have a type. Valid types are
|
|
|
|
<tscreen><verb>
|
|
ro for readonly memory
|
|
rw for read/write memory.
|
|
</verb></tscreen>
|
|
|
|
The linker will assure, that no segment marked as read/write or bss is put
|
|
into a memory area that is marked as readonly.
|
|
|
|
Unused memory in a memory area may be filled. Use the "<tt/fill = yes/"
|
|
attribute to request this. The default value to fill unused space is zero. If
|
|
you don't like this, you may specify a byte value that is used to fill these
|
|
areas with the "<tt/fillval/" attribute. This value is also used to fill unfilled
|
|
areas generated by the assemblers <tt/.ALIGN/ and <tt/.RES/ directives.
|
|
|
|
The symbol <tt/%S/ may be used to access the default start address (that is,
|
|
the one defined in the <ref id="FEATURES" name="FEATURES"> section, or the
|
|
value given on the command line with the <tt><ref id="option-S" name="-S"></tt>
|
|
option).
|
|
|
|
|
|
<sect1>Other SEGMENT attributes<p>
|
|
|
|
Segments may be aligned to some memory boundary. Specify "<tt/align = num/" to
|
|
request this feature. Num must be a power of two. To align all segments on a
|
|
page boundary, use
|
|
|
|
<tscreen><verb>
|
|
SEGMENTS {
|
|
CODE: load = ROM1, type = ro, align = $100;
|
|
RODATA: load = ROM2, type = ro, align = $100;
|
|
DATA: load = ROM2, run = RAM2, type = rw, define = yes,
|
|
align = $100;
|
|
BSS: load = RAM2, type = bss, define = yes, align = $100;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
If an alignment is requested, the linker will add enough space to the output
|
|
file, so that the new segment starts at an address that is dividable by the
|
|
given number without a remainder. All addresses are adjusted accordingly. To
|
|
fill the unused space, bytes of zero are used, or, if the memory area has a
|
|
"<tt/fillval/" attribute, that value. Alignment is always needed, if you have
|
|
used the <tt/.ALIGN/ command in the assembler. The alignment of a segment
|
|
must be equal or greater than the alignment used in the <tt/.ALIGN/ command.
|
|
The linker will check that, and issue a warning, if the alignment of a segment
|
|
is lower than the alignment requested in an <tt/.ALIGN/ command of one of the
|
|
modules making up this segment.
|
|
|
|
For a given segment you may also specify a fixed offset into a memory area or
|
|
a fixed start address. Use this if you want the code to run at a specific
|
|
address (a prominent case is the interrupt vector table which must go at
|
|
address $FFFA). Only one of <tt/ALIGN/ or <tt/OFFSET/ or <tt/START/ may be
|
|
specified. If the directive creates empty space, it will be filled with zero,
|
|
of with the value specified with the "<tt/fillval/" attribute if one is given.
|
|
The linker will warn you if it is not possible to put the code at the
|
|
specified offset (this may happen if other segments in this area are too
|
|
large). Here's an example:
|
|
|
|
<tscreen><verb>
|
|
SEGMENTS {
|
|
VECTORS: load = ROM2, type = ro, start = $FFFA;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
or (for the segment definitions from above)
|
|
|
|
<tscreen><verb>
|
|
SEGMENTS {
|
|
VECTORS: load = ROM2, type = ro, offset = $1FFA;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
The "<tt/align/", "<tt/start/" and "<tt/offset/" attributes change placement
|
|
of the segment in the run memory area, because this is what is usually
|
|
desired. If load and run memory areas are equal (which is the case if only the
|
|
load memory area has been specified), the attributes will also work. There is
|
|
also an "<tt/align_load/" attribute that may be used to align the start of the
|
|
segment in the load memory area, in case different load and run areas have
|
|
been specified. There are no special attributes to set start or offset for
|
|
just the load memory area.
|
|
|
|
To suppress the warning, the linker issues if it encounters a segment that is
|
|
not found in any of the input files, use "<tt/optional=yes/" as additional
|
|
segment attribute. Be careful when using this attribute, because a missing
|
|
segment may be a sign of a problem, and if you're suppressing the warning,
|
|
there is no one left to tell you about it.
|
|
|
|
<sect1>The FILES section<p>
|
|
|
|
The <tt/FILES/ section is used to support other formats than straight binary
|
|
(which is the default, so binary output files do not need an explicit entry
|
|
in the <tt/FILES/ section).
|
|
|
|
The <tt/FILES/ section lists output files and as only attribute the format of
|
|
each output file. Assigning binary format to the default output file would
|
|
look like this:
|
|
|
|
<tscreen><verb>
|
|
FILES {
|
|
%O: format = bin;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
The only other available output format is the o65 format specified by Andre
|
|
Fachat (see the <htmlurl url="http://www.6502.org/users/andre/o65/fileformat.html"
|
|
name="6502 binary relocation format specification">). It is defined like this:
|
|
|
|
<tscreen><verb>
|
|
FILES {
|
|
%O: format = o65;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
The necessary o65 attributes are defined in a special section labeled
|
|
<tt/FORMAT/.
|
|
|
|
|
|
|
|
<sect1>The FORMAT section<p>
|
|
|
|
The <tt/FORMAT/ section is used to describe file formats. The default (binary)
|
|
format has currently no attributes, so, while it may be listed in this
|
|
section, the attribute list is empty. The second supported format,
|
|
<htmlurl url="http://www.6502.org/users/andre/o65/fileformat.html" name="o65">,
|
|
has several attributes that may be defined here.
|
|
|
|
<tscreen><verb>
|
|
FORMATS {
|
|
o65: os = lunix, version = 0, type = small,
|
|
import = LUNIXKERNEL,
|
|
export = _main;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
|
|
|
|
<sect1>The FEATURES section<label id="FEATURES"><p>
|
|
|
|
In addition to the <tt/MEMORY/ and <tt/SEGMENTS/ sections described above, the
|
|
linker has features that may be enabled by an additional section labeled
|
|
<tt/FEATURES/.
|
|
|
|
|
|
<sect2>The CONDES feature<p>
|
|
|
|
<tt/CONDES/ is used to tell the linker to emit module constructor/destructor
|
|
tables.
|
|
|
|
<tscreen><verb>
|
|
FEATURES {
|
|
CONDES: segment = RODATA,
|
|
type = constructor,
|
|
label = __CONSTRUCTOR_TABLE__,
|
|
count = __CONSTRUCTOR_COUNT__;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
The <tt/CONDES/ feature has several attributes:
|
|
|
|
<descrip>
|
|
|
|
<tag><tt>segment</tt></tag>
|
|
|
|
This attribute tells the linker into which segment the table should be
|
|
placed. If the segment does not exist, it is created.
|
|
|
|
|
|
<tag><tt>type</tt></tag>
|
|
|
|
Describes the type of the routines to place in the table. Type may be one of
|
|
the predefined types <tt/constructor/, <tt/destructor/, <tt/interruptor/, or
|
|
a numeric value between 0 and 6.
|
|
|
|
|
|
<tag><tt>label</tt></tag>
|
|
|
|
This specifies the label to use for the table. The label points to the start
|
|
of the table in memory and may be used from within user written code.
|
|
|
|
|
|
<tag><tt>count</tt></tag>
|
|
|
|
This is an optional attribute. If specified, an additional symbol is defined
|
|
by the linker using the given name. The value of this symbol is the number
|
|
of entries (<em/not/ bytes) in the table. While this attribute is optional,
|
|
it is often useful to define it.
|
|
|
|
|
|
<tag><tt>order</tt></tag>
|
|
|
|
Optional attribute that takes one of the keywords <tt/increasing/ or
|
|
<tt/decreasing/ as an argument. Specifies the sorting order of the entries
|
|
within the table. The default is <tt/increasing/, which means that the
|
|
entries are sorted with increasing priority (the first entry has the lowest
|
|
priority). "Priority" is the priority specified when declaring a symbol as
|
|
<tt/.CONDES/ with the assembler, higher values mean higher priority. You may
|
|
change this behaviour by specifying <tt/decreasing/ as the argument, the
|
|
order of entries is reversed in this case.
|
|
|
|
Please note that the order of entries with equal priority is undefined.
|
|
|
|
</descrip>
|
|
|
|
Without specifying the <tt/CONDES/ feature, the linker will not create any
|
|
tables, even if there are <tt/condes/ entries in the object files.
|
|
|
|
For more information see the <tt/.CONDES/ command in the <htmlurl
|
|
url="ca65.html" name="ca65 manual">.
|
|
|
|
|
|
<sect2>The STARTADDRESS feature<p>
|
|
|
|
<tt/STARTADDRESS/ is used to set the default value for the start address,
|
|
which can be referenced by the <tt/%S/ symbol. The builtin default for the
|
|
linker is $200.
|
|
|
|
<tscreen><verb>
|
|
FEATURES {
|
|
# Default start address is $1000
|
|
STARTADDRESS: default = $1000;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
Please note that order is important: The default start address must be defined
|
|
<em/before/ the <tt/%S/ symbol is used in the config file. This does usually
|
|
mean, that the <tt/FEATURES/ section has to go to the top of the config file.
|
|
|
|
|
|
|
|
<sect1>The SYMBOLS section<label id="SYMBOLS"><p>
|
|
|
|
The configuration file may also be used to define symbols used in the link
|
|
stage or to force symbols imports. This is done in the SYMBOLS section. The
|
|
symbol name is followed by a colon and symbol attributes.
|
|
|
|
The following symbol attributes are supported:
|
|
|
|
<descrip>
|
|
|
|
<tag><tt>addrsize</tt></tag>
|
|
|
|
The <tt/addrsize/ attribute specifies the address size of the symbol and
|
|
may be one of
|
|
<itemize>
|
|
<item><tt/zp/, <tt/zeropage/ or <tt/direct/
|
|
<item><tt/abs/, <tt/absolute/ or <tt/near/
|
|
<item><tt/far/
|
|
<item><tt/long/ or <tt/dword/.
|
|
</itemize>
|
|
|
|
Without this attribute, the default address size is <tt/abs/.
|
|
|
|
<tag><tt>type</tt></tag>
|
|
|
|
This attribute is mandatory. Its value is one of <tt/export/, <tt/import/ or
|
|
<tt/weak/. <tt/export/ means that the symbol is defined and exported from
|
|
the linker config. <tt/import/ means that an import is generated for this
|
|
symbol, eventually forcing a module that exports this symbol to be included
|
|
in the output. <tt/weak/ is similar as <tt/export/. However, the symbol is
|
|
only defined if it is not defined elsewhere.
|
|
|
|
<tag><tt>value</tt></tag>
|
|
|
|
This must only be given for symbols of type <tt/export/ or <tt/weak/. It
|
|
defines the value of the symbol and may be an expression.
|
|
|
|
</descrip>
|
|
|
|
The following example defines the stack size for an application, but allows
|
|
the programmer to override the value by specifying <tt/--define
|
|
__STACKSIZE__=xxx/ on the command line.
|
|
|
|
<tscreen><verb>
|
|
SYMBOLS {
|
|
# Define the stack size for the application
|
|
__STACKSIZE__: type = weak, value = $800;
|
|
}
|
|
</verb></tscreen>
|
|
|
|
|
|
|
|
<sect1>Builtin configurations<p>
|
|
|
|
The builtin configurations are part of the linker source. They can be retrieved
|
|
with <tt/--dump-config/ and don't have a special format. So if you need a
|
|
special configuration, it's a good idea to start with the builtin configuration
|
|
for your system. In a first step, just replace <tt/-t target/ by <tt/-C
|
|
configfile/. Then go on and modify the config file to suit your needs.
|
|
|
|
|
|
|
|
<sect1>Secondary configurations<p>
|
|
|
|
Several machine specific binary packages are distributed together with secondary
|
|
configurations (in the cfg directory). These configurations can be used with
|
|
<tt/-C configfile/ too.
|
|
|
|
|
|
|
|
<sect>Special segments<p>
|
|
|
|
The builtin config files do contain segments that have a special meaning for
|
|
the compiler and the libraries that come with it. If you replace the builtin
|
|
config files, you will need the following information.
|
|
|
|
<sect1>INIT<p>
|
|
|
|
The INIT segment is used for initialization code that may be reused once
|
|
execution reaches main() - provided that the program runs in RAM. You
|
|
may for example add the INIT segment to the heap in really memory
|
|
constrained systems.
|
|
|
|
<sect1>LOWCODE<p>
|
|
|
|
For the LOWCODE segment, it is guaranteed that it won't be banked out, so it
|
|
is reachable at any time by interrupt handlers or similar.
|
|
|
|
<sect1>STARTUP<p>
|
|
|
|
This segment contains the startup code which initializes the C software stack
|
|
and the libraries. It is placed in its own segment because it needs to be
|
|
loaded at the lowest possible program address on several platforms.
|
|
|
|
<sect1>ZPSAVE<p>
|
|
|
|
The ZPSAVE segment contains the original values of the zeropage locations used
|
|
by the ZEROPAGE segment. It is placed in its own segment because it must not be
|
|
initialized.
|
|
|
|
|
|
|
|
<sect>Bugs/Feedback<p>
|
|
|
|
If you have problems using the linker, if you find any bugs, or if you're
|
|
doing something interesting with it, I would be glad to hear from you. Feel
|
|
free to contact me by email (<htmlurl url="mailto:uz@cc65.org"
|
|
name="uz@cc65.org">).
|
|
|
|
|
|
|
|
<sect>Copyright<p>
|
|
|
|
ld65 (and all cc65 binutils) are (C) Copyright 1998-2005 Ullrich von
|
|
Bassewitz. For usage of the binaries and/or sources the following
|
|
conditions do apply:
|
|
|
|
This software is provided 'as-is', without any expressed or implied
|
|
warranty. In no event will the authors be held liable for any damages
|
|
arising from the use of this software.
|
|
|
|
Permission is granted to anyone to use this software for any purpose,
|
|
including commercial applications, and to alter it and redistribute it
|
|
freely, subject to the following restrictions:
|
|
|
|
<enum>
|
|
<item> The origin of this software must not be misrepresented; you must not
|
|
claim that you wrote the original software. If you use this software
|
|
in a product, an acknowledgment in the product documentation would be
|
|
appreciated but is not required.
|
|
<item> Altered source versions must be plainly marked as such, and must not
|
|
be misrepresented as being the original software.
|
|
<item> This notice may not be removed or altered from any source
|
|
distribution.
|
|
</enum>
|
|
|
|
|
|
|
|
</article>
|