ld65-5.html

cc65 的编译器文档

<P>So, what your startup code must do, is to copy <CODE>__DATA_SIZE__</CODE> bytes from
<CODE>__DATA_LOAD__</CODE> to <CODE>__DATA_RUN__</CODE> before any other routines are called.
All references to labels in the <CODE>DATA</CODE> segment are relocated to <CODE>RAM2</CODE>
by the linker, so things will work properly.</P>


<H2><A NAME="ss5.5">5.5</A> <A HREF="ld65.html#toc5.5">Other MEMORY area attributes</A>
</H2>


<P>There are some other attributes not covered above. Before starting the
reference section, I will discuss the remaining things here.</P>
<P>You may request symbols definitions also for memory areas. This may be
useful for things like a software stack, or an i/o area.</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        MEMORY {
            STACK:  start = $C000, size = $1000, define = yes;
        }
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>This will define three external symbols that may be used in your code:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        __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.
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>A memory section may also have a type. Valid types are</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        ro      for readonly memory
        rw      for read/write memory.
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>The linker will assure, that no segment marked as read/write or bss is put
into a memory area that is marked as readonly.</P>
<P>Unused memory in a memory area may be filled. Use the "<CODE>fill = yes</CODE>"
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 "<CODE>fillval</CODE>" attribute. This value is also used to fill unfilled
areas generated by the assemblers <CODE>.ALIGN</CODE> and <CODE>.RES</CODE> directives.</P>


<H2><A NAME="ss5.6">5.6</A> <A HREF="ld65.html#toc5.6">Other SEGMENT attributes</A>
</H2>


<P>Segments may be aligned to some memory boundary. Specify "<CODE>align = num</CODE>" to
request this feature. Num must be a power of two. To align all segments on a
page boundary, use</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        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;
        }
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>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 divideable 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
"<CODE>fillval</CODE>" attribute, that value. Alignment is always needed, if you have
the used the <CODE>.ALIGN</CODE> command in the assembler. The alignment of a segment
must be equal or greater than the alignment used in the <CODE>.ALIGN</CODE> command.
The linker will check that, and issue a warning, if the alignment of a segment
is lower than the alignment requested in a <CODE>.ALIGN</CODE> command of one of the
modules making up this segment.</P>
<P>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 <CODE>ALIGN</CODE> or <CODE>OFFSET</CODE> or <CODE>START</CODE> may be
specified. If the directive creates empty space, it will be filled with zero,
of with the value specified with the "<CODE>fillval</CODE>" 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:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        SEGMENTS {
            VECTORS: load = ROM2, type = ro, start = $FFFA;
        }
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>or (for the segment definitions from above)</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        SEGMENTS {
            VECTORS: load = ROM2, type = ro, offset = $1FFA;
        }
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>To suppress the warning, the linker issues if it encounters a segment that is
not found in any of the input files, use "<CODE>optional=yes</CODE>" 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.</P>
<P>File names may be empty, data from segments assigned to a memory area with
an empty file name is discarded. 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.</P>
<P>The symbol <CODE>%S</CODE> may be used to access the default start address (that is,
$200 or the value given on the command line with the <CODE>
<A HREF="ld65-2.html#option-S">-S</A></CODE> option).</P>



<H2><A NAME="ss5.7">5.7</A> <A HREF="ld65.html#toc5.7">The FILES section</A>
</H2>


<P>The <CODE>FILES</CODE> 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 <CODE>FILES</CODE> section).</P>
<P>The <CODE>FILES</CODE> 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:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        FILES {
            %O: format = bin;
        }
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>The only other available output format is the o65 format specified by Andre
Fachat. It is defined like this:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        FILES {
            %O: format = o65;
        }
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>The necessary o65 attributes are defined in a special section labeled
<CODE>FORMAT</CODE>.</P>



<H2><A NAME="ss5.8">5.8</A> <A HREF="ld65.html#toc5.8">The FORMAT section</A>
</H2>


<P>The <CODE>FORMAT</CODE> 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, o65, has
several attributes that may be defined here.</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
    FORMATS {
        o65: os = lunix, version = 0, type = small,
             import = LUNIXKERNEL,
             export = _main;
    }
</PRE>
</CODE></BLOCKQUOTE>
</P>





<H2><A NAME="ss5.9">5.9</A> <A HREF="ld65.html#toc5.9">Features</A>
</H2>


<P>In addition to the <CODE>MEMORY</CODE> and <CODE>SEGMENTS</CODE> sections described above, the
linker has features that may be enabled by an additional section labeled
<CODE>FEATURES</CODE>. Currently, one such feature is available: <CODE>CONDES</CODE> is used
to tell the linker to emit module constructor/destructor tables.</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
        FEATURES {
            CONDES: segment = RODATA,
                    type = constructor,
                    label = __CONSTRUCTOR_TABLE__,
                    count = __CONSTRUCTOR_COUNT__;
        }
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>The <CODE>CONDES</CODE> feature has several attributes:</P>
<P>
<DL>

<DT><B><CODE>segment</CODE></B><DD><P>This attribute tells the linker into which segment the table should be
placed. If the segment does not exist, it is created.</P>


<DT><B><CODE>type</CODE></B><DD><P>Describes the type of the routines to place in the table. Type may be
one of the predefined types <CODE>constructor</CODE> or <CODE>destructor</CODE>, or a
numeric value between 0 and 6.</P>


<DT><B><CODE>label</CODE></B><DD><P>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.</P>


<DT><B><CODE>count</CODE></B><DD><P>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</EM> bytes) in the table. While this
attribute is optional, it is often useful to define it.</P>


<DT><B><CODE>order</CODE></B><DD><P>Optional attribute that takes one of the keywords <CODE>increasing</CODE> or
<CODE>decreasing</CODE> as an argument. Specifies the sorting order of the entries
within the table. The default is <CODE>increasing</CODE>, 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
<CODE>.CONDES</CODE> with the assembler, higher values mean higher priority. You may
change this behaviour by specifying <CODE>decreasing</CODE> as the argument, the
order of entries is reversed in this case.</P>
<P>Please note that the order of entries with equal priority is undefined.</P>

</DL>
</P>
<P>Without specifying the <CODE>CONDES</CODE> feature, the linker will not create any
tables, even if there are <CODE>condes</CODE> entries in the object files.</P>
<P>For more information see the <CODE>.CONDES</CODE> command in the 
<A HREF="ca65.html">ca65 manual</A>.</P>



<H2><A NAME="ss5.10">5.10</A> <A HREF="ld65.html#toc5.10">Builtin configurations</A>
</H2>


<P>The builtin configurations are part of the linker source. They are also
distributed together with the machine specific binary packages (usually in the
doc directory) 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 <CODE>-t target</CODE> by <CODE>-C
configfile</CODE>. The go on and modify the config file to suit your needs.</P>



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