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154 lines
5.3 KiB
ReStructuredText
Tutorial - Writing LLVMCC Configuration files
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=============================================
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LLVMCC is a generic compiler driver (just like ``gcc``), designed to be
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customizable and extensible. Its job is essentially to transform a set
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of input files into a set of targets, depending on configuration rules
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and user options. This tutorial describes how one can write
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configuration files for ``llvmcc``.
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Because LLVMCC uses TableGen [1]_ as the language of its configuration
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files, you need to be familiar with it.
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Describing a toolchain
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----------------------
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The main concept that ``llvmcc`` operates with is a *toolchain*, which
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is just a list of tools that process input files in a pipeline-like
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fashion. Toolchain definitions look like this::
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def ToolChains : ToolChains<[
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ToolChain<[llvm_gcc_c, llc, llvm_gcc_assembler, llvm_gcc_linker]>,
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ToolChain<[llvm_gcc_cpp, llc, llvm_gcc_assembler, llvm_gcc_linker]>,
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...
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]>;
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Every configuration file should have a single toolchains list called
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``ToolChains``.
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At the time of writing, ``llvmcc`` does not support mixing various
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toolchains together - in other words, all input files should be in the
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same language.
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Another temporary limitation is that every toolchain should end with a
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"join" node - a linker-like program that combines its inputs into a
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single output file.
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Describing a tool
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-----------------
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A single element of a toolchain is a tool. A tool definition looks
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like this (taken from the Tools.td file)::
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def llvm_gcc_cpp : Tool<[
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(in_language "c++"),
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(out_language "llvm-assembler"),
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(output_suffix "bc"),
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(cmd_line "llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm"),
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(sink)
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]>;
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This defines a new tool called ``llvm_gcc_cpp``, which is an alias for
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``llvm-g++``. As you can see, a tool definition is just a list of
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properties; most of them should be self-evident. The ``sink`` property
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means that this tool should be passed all command-line options that
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aren't handled by the other tools.
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The complete list of the currently implemented tool properties follows:
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* Possible tool properties:
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- in_language - input language name.
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- out_language - output language name.
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- output_suffix - output file suffix.
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- cmd_line - the actual command used to run the tool. You can use
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``$INFILE`` and ``$OUTFILE`` variables.
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- join - this tool is a "join node" in the graph, i.e. it gets a
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list of input files and joins them together. Used for linkers.
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- sink - all command-line options that are not handled by other
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tools are passed to this tool.
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The next tool definition is slightly more complex::
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def llvm_gcc_linker : Tool<[
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(in_language "object-code"),
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(out_language "executable"),
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(output_suffix "out"),
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(cmd_line "llvm-gcc $INFILE -o $OUTFILE"),
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(join),
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(prefix_list_option "L", (forward), (help "add a directory to link path")),
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(prefix_list_option "l", (forward), (help "search a library when linking")),
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(prefix_list_option "Wl", (unpack_values), (help "pass options to linker"))
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]>;
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This tool has a "join" property, which means that it behaves like a
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linker (because of that this tool should be the last in the
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toolchain). This tool also defines several command-line options: ``-l``,
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``-L`` and ``-Wl`` which have their usual meaning. An option has two
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attributes: a name and a (possibly empty) list of properties. All
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currently implemented option types and properties are described below:
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* Possible option types:
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- switch_option - a simple boolean switch, for example ``-time``.
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- parameter_option - option that takes an argument, for example ``-std=c99``;
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- parameter_list_option - same as the above, but more than one
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occurence of the option is allowed.
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- prefix_option - same as the parameter_option, but the option name
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and parameter value are not separated.
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- prefix_list_option - same as the above, but more than one
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occurence of the option is allowed; example: ``-lm -lpthread``.
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* Possible option properties:
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- append_cmd - append a string to the tool invocation command.
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- forward - forward this option unchanged.
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- stop_compilation - stop compilation after this phase.
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- unpack_values - used for for splitting and forwarding
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comma-separated lists of options, e.g. ``-Wa,-foo=bar,-baz`` is
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converted to ``-foo=bar -baz`` and appended to the tool invocation
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command.
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- help - help string associated with this option.
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- required - this option is obligatory.
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Language map
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------------
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One last bit that you probably should change is the language map,
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which defines mappings between language names and file extensions. It
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is used internally to choose the proper toolchain based on the names
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of the input files. Language map definition is located in the file
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``Tools.td`` and looks like this::
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def LanguageMap : LanguageMap<
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[LangToSuffixes<"c++", ["cc", "cp", "cxx", "cpp", "CPP", "c++", "C"]>,
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LangToSuffixes<"c", ["c"]>,
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...
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]>;
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Putting it all together
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-----------------------
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Since at the time of writing LLVMCC does not support on-the-fly
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reloading of the configuration, the only way to test your changes is
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to recompile the program. To do this, ``cd`` to the source code
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directory and run ``make``.
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References
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==========
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.. [1] TableGen Fundamentals
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http://llvm.cs.uiuc.edu/docs/TableGenFundamentals.html
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