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Merge pull request #2000 from bbbradsmith/doc_cc65_intern_linker_config

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Document expected linker configuration and special segments used by cc65
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Bob Andrews 2023-02-21 22:00:23 +01:00 committed by GitHub
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doc/cc65-intern.sgml
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<abstract>
Internal details of cc65 code generation,
such as calling assembly functions from C.
such as the expected linker configuration,
and calling assembly functions from C.
</abstract>
<!-- Table of contents -->
@ -16,6 +17,76 @@ such as calling assembly functions from C.
<sect>Linker configuration<p>
The C libraries and code generation depend directly on a suitable linker configuration.
There are premade configuration files in the <tt/cfg&sol;/ directory, normally chosen by the
linker's selected target. These can be used as a template for customization.
The C libraries depend on several special segments to be defined in your linker configuration.
Generated code will also use some of them by default.
Some platform libraries have additional special segments.
Memory areas are free to be defined in a way that is appropriate to each platform,
and the segments they contain are used as a layer of semantics and abstraction,
to allow much of the reorganization to be done with the linker config,
rather than requiring platform-specific code source changes.
<sect1><tt/ZEROPAGE/ segment<p>
Used by the C library and generated code for efficient internal and temporary state storage,
also called "pseudo-registers".
<sect1><tt/STARTUP/ segment<p>
Used by each platform instance of the C library in <tt/crt0.s/ to contain the entry point
of the program.
The startup module will export <tt/__STARTUP__ : absolute = 1/ to force the linker to
always include <tt/crt0.s/ from the library.
<sect1><tt/CODE/ segment<p>
The default segment for generated code, and most C library code will be located here.
Use <tt/#pragma code-name/ to redirect generated code to another segment.
<sect1><tt/BSS/ segment<p>
Used for uninitialized variables.
Originally an acronym for "Block Started by Symbol", but the meaning of this is now obscure.
Use <tt/#pragma bss-name/ to redirect uninitialized variables to another segment.
<sect1><tt/DATA/ segment<p>
Used for initialized variables.
On some platforms, this may be initialized as part of the program loading process,
but on others it may have a separate <tt/LOAD/ and <tt/RUN/ address,
allowing <tt/copydata/ to copy the initialization from the loaded location
into their run destination in RAM.
Use <tt/#pragma data-name/ to redirect initialized variables to another segment.
<sect1><tt/RODATA/ segment<p>
Used for read-only (constant) data.
Use <tt/#pragma rodata-name/ to redirect constant data to another segment.
<sect1><tt/FEATURES/ table<p>
This currently defines table locations for the <tt/CONDES/
constructor, destructor, and interruptor features.
Some platform libraries use these.
The constructors will be called with <tt/initlib/ at startup,
and the destructors with <tt/donelib/ at program exit.
Interruptors are called with <tt/callirq/.
<sect>Calling assembly functions from C<p>
<sect1>Calling conventions<p>

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doc/index.sgml
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Contains hints on creating the most effective code with cc65.
<tag><htmlurl url="cc65-intern.html" name="cc65-intern.html"></tag>
Describes internal details of cc65, such as calling conventions.
Describes internal details of cc65: linker configuration, calling conventions, etc.
<tag><htmlurl url="using-make.html" name="using-make.html"></tag>
Build programs, using the GNU Make utility.