-<!doctype linuxdoc system>
+<!doctype linuxdoc system> <!-- -*- text-mode -*- -->
<article>
<title>ld65 Users Guide
-<author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
-<date>02.12.2000, 02.10.2001
+<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">
<abstract>
The ld65 linker combines object files into an executable file. ld65 is highly
<itemize>
-<item> Accept any number of segments to form an executable module.
+<item> Accept any number of segments to form an executable module.
-<item> Resolve arbitrary expressions stored in the object files.
+<item> Resolve arbitrary expressions stored in the object files.
-<item> In case of errors, use the meta information stored in the object files
- to produce helpful error messages. In case of undefined symbols,
- expression range errors, or symbol type mismatches, ld65 is able to
- tell you the exact location in the original assembler source, where
- the symbol was referenced.
+<item> In case of errors, use the meta information stored in the object files
+ to produce helpful error messages. In case of undefined symbols,
+ expression range errors, or symbol type mismatches, ld65 is able to
+ tell you the exact location in the original assembler source, where
+ the symbol was referenced.
-<item> Flexible output. The output of ld65 is highly configurable by a config
- file. More common platforms are supported by builtin configurations
- that may be activated by naming the target system. The output
- generation was designed with different output formats in mind, so
- adding other formats shouldn't be a great problem.
+<item> Flexible output. The output of ld65 is highly configurable by a config
+ file. Some more-common platforms are supported by default configurations
+ that may be activated by naming the target system. The output
+ generation was designed with different output formats in mind, so
+ adding other formats shouldn't be a great problem.
</itemize>
<sect>Usage<p>
-<sect1>Command
line option overview<p>
+<sect1>Command
-line option overview<p>
The linker is called as follows:
-m name Create a map file
-o name Name the default output file
-t sys Set the target system
- -u sym Force an import of symbol `sym'
+ -u sym Force an import of symbol 'sym'
-v Verbose mode
-vm Verbose map file
Long options:
- --cfg-path path Specify a config file search path
- --config name Use linker config file
- --dbgfile name Generate debug information
- --define sym=val Define a symbol
- --dump-config name Dump a builtin configuration
- --end-group End a library group
- --force-import sym Force an import of symbol `sym'
- --help Help (this text)
- --lib file Link this library
- --lib-path path Specify a library search path
- --mapfile name Create a map file
- --module-id id Specify a module id
- --obj file Link this object file
- --obj-path path Specify an object file search path
- --start-addr addr Set the default start address
- --start-group Start a library group
- --target sys Set the target system
- --version Print the linker version
+ --allow-multiple-definition Allow multiple definitions
+ --cfg-path path Specify a config file search path
+ --config name Use linker config file
+ --dbgfile name Generate debug information
+ --define sym=val Define a symbol
+ --end-group End a library group
+ --force-import sym Force an import of symbol 'sym'
+ --help Help (this text)
+ --lib file Link this library
+ --lib-path path Specify a library search path
+ --mapfile name Create a map file
+ --module-id id Specify a module id
+ --obj file Link this object file
+ --obj-path path Specify an object file search path
+ --start-addr addr Set the default start address
+ --start-group Start a library group
+ --target sys Set the target system
+ --version Print the linker version
---------------------------------------------------------------------------
</verb></tscreen>
-<sect1>Command
line options in detail<p>
+<sect1>Command
-line options in detail<p>
-Here is a description of all the command line options:
+Here is a description of all of the command-line options:
<descrip>
+ <tag><tt>--allow-multiple-definition</tt></tag>
+
+ Normally when a global symbol is defined multiple times, ld65 will
+ issue an error and not create the output file. This option lets it
+ silently ignore this fact and continue. The first definition of a
+ symbol will be used.
+
+
<label id="option--start-group">
<tag><tt>-(, --start-group</tt></tag>
Start a library group. The libraries specified within a group are searched
multiple times to resolve crossreferences within the libraries. Normally,
- crossreferences are only resolved within a library, that is the library is
+ crossreferences are resolved only within a library, that is the library is
searched multiple times. Libraries specified later on the command line
cannot reference otherwise unreferenced symbols in libraries specified
earlier, because the linker has already handled them. Library groups are
<tag><tt>-o name</tt></tag>
The -o switch is used to give the name of the default output file.
- Depending on your output configuration, this name may NOT be used as
- name for the output file. However, for the builtin configurations, this
+ Depending on your output configuration, this name <em/might not/ be used as the
+ name for the output file. However, for the default configurations, this
name is used for the output file name.
<tag><tt>-t sys, --target sys</tt></tag>
The argument for the -t switch is the name of the target system. Since this
- switch will activate a builtin configuration, it may not be used together
+ switch will activate a default configuration, it may not be used together
with the <tt><ref id="option-C" name="-C"></tt> option. The following target
systems are currently supported:
<item>module
<item>apple2
<item>apple2enh
- <item>apple-geos
+ <item>atari2600
<item>atari
+ <item>atarixl
<item>atmos
<item>c16 (works also for the c116 with memory up to 32K)
<item>c64
<item>c128
- <item>cbm510 (CBM-II series with 40 column video)
- <item>cbm610 (all CBM series-II computers with 80 column video)
- <item>cbm-geos
+ <item>cbm510 (CBM-II series with 40-column video)
+ <item>cbm610 (all CBM series-II computers with 80-column video)
+ <item>geos-apple
+ <item>geos-cbm
<item>lunix
<item>lynx
<item>nes
<item>pet (all CBM PET systems except the 2001)
<item>plus4
+ <item>sim6502
+ <item>sim65c02
<item>supervision
+ <item>telestrat
<item>vic20
</itemize>
Force an import of a symbol. While object files are always linked to the
output file, regardless if there are any references, object modules from
libraries get only linked in if an import can be satisfied by this module.
- The <tt/--fore-import/ option may be used to add a reference to a symbol and
+ The <tt/--force-import/ option may be used to add a reference to a symbol and
as a result force linkage of the module that exports the identifier.
- The name of the symbol may optionally be followed by a colon and an address
- size specifier. If no address size is specified, the default address size
+ The name of the symbol may optionally be followed by a colon and an address-size
+ specifier. If no address size is specified, the default address size
for the target machine is used.
Please note that the symbol name needs to have the internal representation,
- meaning you have to prepend an underline for C identifiers.
+ meaning you have to prepend an underscore for C identifiers.
<label id="option-v">
Must be used in conjunction with <tt><ref id="option-m" name="-m"></tt>
(generate map file). Normally the map file will not include empty segments
and sections, or unreferenced symbols. Using this option, you can force the
- linker to include all this information into the map file.
+ linker to include all that information into the map file. Also, it will
+ include a second <tt/Exports/ list. The first list is sorted by name;
+ the second one is sorted by value.
<label id="option-C">
This option allows to define an external symbol on the command line. Value
may start with a '$' sign or with <tt/0x/ for hexadecimal values,
- otherwise a leading zero denotes octal values. See also the <ref
- id="SYMBOLS" name="SYMBOLS section"> in the configuration file.
+ otherwise a leading zero denotes octal values. See also <ref
+ id="SYMBOLS" name="the SYMBOLS section"> in the configuration file.
<label id="option--lib-path">
Specify a library search path. This option may be used more than once. It
adds a directory to the search path for library files. Libraries specified
- without a path are searched in current directory, in the directory given in
- the <tt/LD65_LIB/ environment variable, and in the list of directories
- specified using <tt/--lib-path/.
+ without a path are searched in the current directory, in the list of
+ directories specified using <tt/--lib-path/, in directories given by
+ environment variables, and in a built-in default directory.
<tag><tt>-Ln</tt></tag>
This option allows you to create a file that contains all global labels and
- may be loaded into VICE emulator using the <tt/ll/ (load label) command. You
+ may be loaded into the VICE emulator using the <tt/ll/ (load label) command
+ or into the Oricutron emulator using the <tt/sl/ (symbols load) command. You
may use this to debug your code with VICE. Note: Older versions had some
- bugs in the label code. If you have problems, please get the latest VICE
- version.
+ bugs in the label code. If you have problems, please get the latest <url
+ url="http://vice-emu.sourceforge.net" name="VICE"> version.
<label id="option-S">
<tag><tt>-S addr, --start-addr addr</tt></tag>
Using -S you may define the default starting address. If and how this
- address is used depends on the config file in use. For the builtin
+ address is used depends on the config file in use. For the default
configurations, only the "none", "apple2" and "apple2enh" systems honor an
- explicit start address, all other builtin config provide their own.
+ explicit start address, all other default configs provide their own.
<tag><tt>-V, --version</tt></tag>
- This option print the version number of the linker. If you send any
+ This option prints the version number of the linker. If you send any
suggestions or bugfixes, please include this number.
Specify a config file search path. This option may be used more than once.
It adds a directory to the search path for config files. A config file given
with the <tt><ref id="option-C" name="-C"></tt> option that has no path in
- its name is searched in the current directory, in the directory given in the
- <tt/LD65_CFG/ environment variable, and in the list of directories specified
- using <tt/--cfg-path/.
+ its name is searched in the current directory, in the list of directories
+ specified using <tt/--cfg-path/, in directories given by environment variables,
+ and in a built-in default directory.
<label id="option--dbgfile">
<tag><tt>--lib file</tt></tag>
- Links a library to the output. Use this command line option instead of just
+ Links a library to the output. Use this command-line option instead of just
naming the library file, if the linker is not able to determine the file
type because of an unusual extension.
<tag><tt>--obj file</tt></tag>
- Links an object file to the output. Use this command line option instead
+ Links an object file to the output. Use this command-line option instead
of just naming the object file, if the linker is not able to determine the
file type because of an unusual extension.
Specify an object file search path. This option may be used more than once.
It adds a directory to the search path for object files. An object file
- passed to the linker that has no path in its name is searched in current
- directory, in the directory given in the <tt/LD65_OBJ/ environment variable,
- and in the list of directories specified using <tt/--obj-path/.
+ passed to the linker that has no path in its name is searched in the current
+ directory, in the list of directories specified using <tt/--obj-path/, in
+ directories given by environment variables, and in a built-in default directory.
</descrip>
<sect>Search paths<p>
-Starting with version 2.10 there are now several search paths for files needed
-by the linker: One for libraries, one for object files and one for config
+Starting with version 2.10, there are now several search-path lists for files needed
+by the linker: one for libraries, one for object files, and one for config
files.
<sect1>Library search path<p>
-The library search path contains in this order:
+The library search-path list contains in this order:
<enum>
<item>The current directory.
-<item>A compiled in library path which is often <tt>/usr/lib/cc65/lib</tt> on
- Linux systems.
+<item>Any directory added with the <tt><ref id="option--lib-path"
+ name="--lib-path"></tt> option on the command line.
<item>The value of the environment variable <tt/LD65_LIB/ if it is defined.
<item>A subdirectory named <tt/lib/ of the directory defined in the environment
variable <tt/CC65_HOME/, if it is defined.
-<item>Any directory added with the <tt><ref id="option--lib-path"
- name="--lib-path"></tt> option on the command line.
+<item>An optionally compiled-in library path.
</enum>
<sect1>Object file search path<p>
-The object file search path contains in this order:
+The object file search-path list contains in this order:
<enum>
<item>The current directory.
-<item>A compiled in directory which is often <tt>/usr/lib/cc65/obj</tt> on
- Linux systems.
+<item>Any directory added with the <tt><ref id="option--obj-path"
+ name="--obj-path"></tt> option on the command line.
<item>The value of the environment variable <tt/LD65_OBJ/ if it is defined.
<item>A subdirectory named <tt/obj/ of the directory defined in the environment
variable <tt/CC65_HOME/, if it is defined.
-<item>Any directory added with the <tt><ref id="option--obj-path"
- name="--obj-path"></tt> option on the command line.
+<item>An optionally compiled-in directory.
</enum>
<sect1>Config file search path<p>
-The config file search path contains in this order:
+The config file search-path list contains in this order:
<enum>
<item>The current directory.
-<item>A compiled in directory which is often <tt>/usr/lib/cc65/cfg</tt> on
- Linux systems.
+<item>Any directory added with the <tt><ref id="option--cfg-path"
+ name="--cfg-path"></tt> option on the command line.
<item>The value of the environment variable <tt/LD65_CFG/ if it is defined.
<item>A subdirectory named <tt/cfg/ of the directory defined in the environment
variable <tt/CC65_HOME/, if it is defined.
-<item>Any directory added with the <tt><ref id="option--cfg-path"
- name="--cfg-path"></tt> option on the command line.
+<item>An optionally compiled-in directory.
</enum>
special naming conventions), all modules in the library are checked if an
export from this module would satisfy an import from other modules. All
modules where this is the case are marked. If duplicate identifiers are
-found, the linker issues a warning.
+found, the linker issues warnings.
-This procedure (parsing and reading from left to right) does mean, that a
+That procedure (parsing and reading from left to right) does mean that a
library may only satisfy references for object modules (given directly or from
a library) named <em/before/ that library. With the command line
<tscreen><verb>
- ld65 crt0.o clib.lib test.o
+ ld65 crt0.o clib.lib test.o
</verb></tscreen>
-the module test.o may not contain references to modules in the library
-clib.lib. If this is the case, you have to change the order of the modules
+the module <tt/test.o/ must not contain references to modules in the library
+<tt/clib.lib/. But, if it does, you have to change the order of the modules
on the command line:
<tscreen><verb>
- ld65 crt0.o test.o clib.lib
+ ld65 crt0.o test.o clib.lib
</verb></tscreen>
Step two is, to read the configuration file, and assign start addresses
After that, the linker is ready to produce an output file. Before doing that,
it checks its data for consistency. That is, it checks for unresolved
externals (if the output format is not relocatable) and for symbol type
-mismatches (for example a zero page symbol is imported by a module as absolute
+mismatches (for example a zero-page symbol is imported by a module as an absolute
symbol).
Step four is, to write the actual target files. In this step, the linker will
And, last step, if you give the <tt><ref id="option-v" name="-v"></tt> switch
twice, you get a dump of the segment data. However, this may be quite
-unreadable if you're not a developer:-)
+unreadable if you're not a developer. :-)
<sect1>Memory areas<p>
-Memory areas are specified in a <tt/MEMORY/ section. Lets have a look at an
+Memory areas are specified in a <tt/MEMORY/ section. Let's have a look at an
example (this one describes the usable memory layout of the C64):
<tscreen><verb>
- MEMORY {
- RAM1: start = $0800, size = $9800;
- ROM1: start = $A000, size = $2000;
- RAM2: start = $C000, size = $1000;
- ROM2: start = $E000, size = $2000;
- }
+ MEMORY {
+ RAM1: start = $0800, size = $9800;
+ ROM1: start = $A000, size = $2000;
+ RAM2: start = $C000, size = $1000;
+ ROM2: start = $E000, size = $2000;
+ }
</verb></tscreen>
-As you can see, there are two ram areas and two rom areas. The names
+As you can see, there are two RAM areas and two ROM areas. The names
(before the colon) are arbitrary names that must start with a letter, with
the remaining characters being letters or digits. The names of the memory
areas are used when assigning segments. As mentioned above, case is
-significant for these names.
+significant for those names.
The syntax above is used in all sections of the config file. The name
(<tt/ROM1/ etc.) is said to be an identifier, the remaining tokens up to the
have looked like this:
<tscreen><verb>
- # Start of memory section
- MEMORY
- {
- RAM1:
- start $0800
- size $9800;
- ROM1:
- start $A000
- size $2000;
- RAM2:
- start $C000
- size $1000;
- ROM2:
- start $E000
- size $2000;
- }
+ # Start of memory section
+ MEMORY
+ {
+ RAM1:
+ start $0800
+ size $9800;
+ ROM1:
+ start $A000
+ size $2000;
+ RAM2:
+ start $C000
+ size $1000;
+ ROM2:
+ start $E000
+ size $2000;
+ }
</verb></tscreen>
There are of course more attributes for a memory section than just start and
size. Start and size are mandatory attributes, that means, each memory area
defined <em/must/ have these attributes given (the linker will check that). I
will cover other attributes later. As you may have noticed, I've used a
-comment in the example above. Comments start with a hash mark (`#'), the
+comment in the example above. Comments start with a hash mark ('#'), the
remainder of the line is ignored if this character is found.
section:
<tscreen><verb>
- SEGMENTS {
- CODE: load = RAM1, type = ro;
- RODATA: load = RAM1, type = ro;
- DATA: load = RAM1, type = rw;
- BSS: load = RAM1, type = bss, define = yes;
- }
+ SEGMENTS {
+ CODE: load = RAM1, type = ro;
+ RODATA: load = RAM1, type = ro;
+ DATA: load = RAM1, type = rw;
+ BSS: load = RAM1, type = bss, define = yes;
+ }
</verb></tscreen>
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:
+segment. Why? Here enters the segment type: For each segment specified, you may also
+specify a segment attribute. There are five possible segment attributes:
<tscreen><verb>
- ro means readonly
- rw means read/write
- bss means that this is an uninitialized segment
- zp a zeropage segment
+ ro means readonly
+ rw means read/write
+ bss means that this is an uninitialized segment
+ zp a zeropage segment
+ overwrite a segment that overwrites (parts of) another one
+
</verb></tscreen>
So, because we specified that the segment with the name BSS is of type bss,
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 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.
+ __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
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
+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
+that better) takes a string enclosed in double quotes ('&dquot;') 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";
- }
+ 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:
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.
+to it. This is useful, if the 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";
- }
+ 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
'%' is used as an escape char, the sequence "%%" has to be used if a single
percent sign is required.
+<sect1>OVERWRITE segments<p>
+
+There are situations when you may wish to overwrite some part (or parts) of a
+segment with another one. Perhaps you are modifying an OS ROM that has its
+public subroutines at fixed, well-known addresses, and you want to prevent them
+from shifting to other locations in memory if your changed code takes less
+space. Or you are updating a block of code available in binary-only form with
+fixes that are scattered in various places. Generally, whenever you want to
+minimize disturbance to an existing code brought on by your updates, OVERWRITE
+segments are worth considering.
+
+Here is an example:
+
+<tscreen><verb>
+MEMORY {
+ RAM: file = "", start = $6000, size = $2000, type=rw;
+ ROM: file = %O, start = $8000, size = $8000, type=ro;
+}
+</verb></tscreen>
+
+Nothing unusual so far, just two memory blocks - one RAM, one ROM. Now let's
+look at the segment configuration:
+
+<tscreen><verb>
+SEGMENTS {
+ RAM: load = RAM, type = bss;
+ ORIGINAL: load = ROM, type = ro;
+ FASTCOPY: load = ROM, start=$9000, type = overwrite;
+ JMPPATCH1: load = ROM, start=$f7e8, type = overwrite;
+ DEBUG: load = ROM, start=$8000, type = overwrite;
+ VERSION: load = ROM, start=$e5b7, type = overwrite;
+}
+</verb></tscreen>
+
+Segment named ORIGINAL contains the original code, disassembled or provided in
+a binary form (i.e. using <tt/.INCBIN/ directive; see the <tt/ca65/ assembler
+document). Subsequent four segments will be relocated to addresses specified
+by their "start" attributes ("offset" can also be used) and then will overwrite
+whatever was at these locations in the ORIGINAL segment. In the end, resulting
+binary output file will thus contain original data with the exception of four
+sequences starting at $9000, $f7e8, $8000 and $e5b7, which will sport code from
+their respective segments. How long these sequences will be depends on the
+lengths of corresponding segments - they can even overlap, so think what you're
+doing.
+
+Finally, note that OVERWRITE segments should be the final segments loaded to a
+particular memory area, and that they need at least one of "start" or "offset"
+attributes specified.
+
<sect1>LOAD and RUN addresses (ROMable code)<p>
Let us look now at a more complex example. Say, you've successfully tested
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
+ 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
+startup. Since there's no way to remember the contents of the data segment,
+other 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.
+The linker won't copy the data from ROM into RAM for you (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
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;
- }
+ 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
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.
+ __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
All references to labels in the <tt/DATA/ segment are relocated to <tt/RAM2/
by the linker, so things will work properly.
+There's a library subroutine called <tt/copydata/ (in a module named
+<tt/copydata.s/) that might be used to do actual copying. Be sure to have a
+look at it's inner workings before using it!
+
<sect1>Other MEMORY area attributes<p>
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.
+useful for things like a software stack, or an I/O area.
<tscreen><verb>
- MEMORY {
- STACK: start = $C000, size = $1000, define = yes;
- }
+ MEMORY {
+ STACK: start = $C000, size = $1000, define = yes;
+ }
</verb></tscreen>
This will define some 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.
+ __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 is 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.
__STACK_FILEOFFS__ The binary offset in the output file. This
is not defined for relocatable output file
formats (o65).
-</verb></tscreen>
+</verb></tscreen>
A memory section may also have a type. Valid types are
<tscreen><verb>
- ro for readonly memory
- rw for read/write memory.
+ 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
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.
+areas with the "<tt/fillval/" attribute. If there is no "<tt/fillval/"
+attribute for the segment, the "<tt/fillval/" attribute of the memory area (or
+its default) is used instead. This means that the value may also be used to
+fill unfilled areas generated by the assembler's <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
+the one defined in <ref id="FEATURES" name="the FEATURES section">, or the
value given on the command line with the <tt><ref id="option-S" name="-S"></tt>
option).
+To support systems with banked memory, a special attribute named <tt/bank/ is
+available. The attribute value is an arbitrary 32-bit integer. The assembler
+has a builtin function named <tt/.BANK/ which may be used with an argument
+that has a segment reference (for example a symbol). The result of this
+function is the value of the bank attribute for the run memory area of the
+segment.
+
<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
+request this feature. 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;
- }
+ 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
large). Here's an example:
<tscreen><verb>
- SEGMENTS {
- VECTORS: load = ROM2, type = ro, start = $FFFA;
- }
+ 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;
- }
+ SEGMENTS {
+ VECTORS: load = ROM2, type = ro, offset = $1FFA;
+ }
</verb></tscreen>
The "<tt/align/", "<tt/start/" and "<tt/offset/" attributes change placement
been specified. There are no special attributes to set start or offset for
just the load memory area.
+A "<tt/fillval/" attribute may not only be specified for a memory area, but
+also for a segment. The value must be an integer between 0 and 255. It is used
+as the fill value for space reserved by the assembler's <tt/.ALIGN/ and <tt/.RES/
+commands. It is also used as the fill value for space between sections (part of a
+segment that comes from one object file) caused by alignment, but not for
+space that preceeds the first section.
+
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
+not found in any of the input files, use "<tt/optional=yes/" as an 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.
look like this:
<tscreen><verb>
- FILES {
- %O: format = bin;
- }
+ 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"
+There are two other available formats, one is the o65 format specified by Andre
+Fachat (see the <url 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;
- }
+ FILES {
+ %O: format = o65;
+ }
+</verb></tscreen>
+
+The other format available is the Atari (xex) segmented file format, this is
+the standard format used by Atari DOS 2.0 and upward file managers in the Atari
+8-bit computers, and it is defined like this:
+
+<tscreen><verb>
+ FILES {
+ %O: format = atari;
+ }
</verb></tscreen>
-The necessary o65 attributes are defined in a special section labeled
-<tt/FORMAT/.
+In the Atari segmented file format, the linker will write each <tt/MEMORY/ area
+as a new segment, including a header with the start and end address.
+
+The necessary o65 or Atari attributes are defined in a special section labeled
+<ref id="FORMAT" name="FORMAT">.
-<sect1>The FORMAT section<p>
+<sect1>The FORMAT section<label id="FORMAT"><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">,
+<url url="http://www.6502.org/users/andre/o65/fileformat.html" name="o65">,
has several attributes that may be defined here.
<tscreen><verb>
}
</verb></tscreen>
+The Atari file format has two attributes:
+
+<descrip>
+
+ <tag><tt>RUNAD = symbol</tt></tag>
+
+ Specify a symbol as the run address of the binary, the loader will call this
+ address after all the file is loaded in memory. If the attribute is omitted,
+ no run address is included in the file.
+
+ <tag><tt>INITAD = memory_area : symbol</tt></tag>
+
+ Specify a symbol as the initialization address for the given memory area.
+ The binary loader will call this address just after the memory area is loaded
+ into memory, before continuing loading the rest of the file.
+
+</descrip>
+
+
+<tscreen><verb>
+ FORMATS {
+ atari: runad = _start;
+ }
+</verb></tscreen>
<sect1>The FEATURES section<label id="FEATURES"><p>
tables.
<tscreen><verb>
- FEATURES {
- CONDES: segment = RODATA,
- type = constructor,
- label = __CONSTRUCTOR_TABLE__,
- count = __CONSTRUCTOR_COUNT__;
- }
+ FEATURES {
+ CONDES: segment = RODATA,
+ type = constructor,
+ label = __CONSTRUCTOR_TABLE__,
+ count = __CONSTRUCTOR_COUNT__;
+ }
</verb></tscreen>
The <tt/CONDES/ feature has several attributes:
<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.
+ of the table in memory and may be used from within user-written code.
<tag><tt>count</tt></tag>
<tag><tt>order</tt></tag>
- Optional attribute that takes one of the keywords <tt/increasing/ or
+ An 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
Please note that the order of entries with equal priority is undefined.
+ <tag><tt>import</tt></tag>
+
+ This attribute defines a valid symbol name, that is added as an import
+ to the modules defining a constructor/destructor of the given type.
+ This can be used to force linkage of a module if this module exports the
+ requested symbol.
+
</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
+For more information see the <tt/.CONDES/ command in the <url
url="ca65.html" name="ca65 manual">.
linker is $200.
<tscreen><verb>
- FEATURES {
+ FEATURES {
# Default start address is $1000
- STARTADDRESS: default = $1000;
- }
+ STARTADDRESS: default = $1000;
+ }
</verb></tscreen>
Please note that order is important: The default start address must be defined
__STACKSIZE__=xxx/ on the command line.
<tscreen><verb>
- SYMBOLS {
+ SYMBOLS {
# Define the stack size for the application
- __STACKSIZE__: type = weak, value = $800;
- }
+ __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.
-The INIT segment is used for initialization code that may be reused once
+The ONCE segment is used for initialization code run only once before
execution reaches main() - provided that the program runs in RAM. You
-may for example add the INIT segment to the heap in really memory
+may for example add the ONCE segment to the heap in really memory
constrained systems.
<sect1>LOWCODE<p>
-<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
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.
+<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>
projects / cc65 / blobdiff