[PATCH 25/27] Documentation: add "internals" subdirectory

[David Malcolm <dmalcolm@redhat.com>]

This final part of the documentation is a guide to the internals of
the library, aimed at current and future contributors to the library
(including myself).

gcc/jit/
	* docs/internals/index.rst: New.
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 gcc/jit/docs/internals/index.rst | 216 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 216 insertions(+)
 create mode 100644 gcc/jit/docs/internals/index.rst

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+.. Copyright (C) 2014 Free Software Foundation, Inc.
+   Originally contributed by David Malcolm <dmalcolm@redhat.com>
+
+   This is free software: you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see
+   <http://www.gnu.org/licenses/>.
+
+Internals
+=========
+
+Working on the JIT library
+--------------------------
+Having checked out the source code (to "src"), you can configure and build
+the JIT library like this:
+
+.. code-block:: bash
+
+  mkdir build
+  mkdir install
+  PREFIX=$(pwd)/install
+  cd build
+  ../src/configure \
+     --enable-host-shared \
+     --enable-languages=jit \
+     --disable-bootstrap \
+     --enable-checking=release \
+     --prefix=$PREFIX
+  nice make -j4 # altering the "4" to however many cores you have
+
+This should build a libgccjit.so within jit/build/gcc:
+
+.. code-block:: console
+
+ [build] $ file gcc/libgccjit.so*
+ gcc/libgccjit.so:       symbolic link to `libgccjit.so.0'
+ gcc/libgccjit.so.0:     symbolic link to `libgccjit.so.0.0.1'
+ gcc/libgccjit.so.0.0.1: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, not stripped
+
+Here's what those configuration options mean:
+
+.. option:: --enable-host-shared
+
+  Configuring with this option means that the compiler is built as
+  position-independent code, which incurs a slight performance hit,
+  but it necessary for a shared library.
+
+.. option:: --enable-languages=jit
+
+  This specifies which frontends to build.  The JIT library looks like
+  a frontend to the rest of the code.
+
+.. option:: --disable-bootstrap
+
+  For hacking on the "jit" subdirectory, performing a full
+  bootstrap can be overkill, since it's unused by a bootstrap.  However,
+  when submitting patches, you should remove this option, to ensure that
+  the compiler can still bootstrap itself.
+
+.. option:: --enable-checking=release
+
+  The compile can perform extensive self-checking as it runs, useful when
+  debugging, but slowing things down.
+
+  For maximum speed, configure with ``--enable-checking=release`` to
+  disable this self-checking.
+
+Running the test suite
+----------------------
+
+.. code-block:: console
+
+  [build] $ cd gcc
+  [gcc] $ make check-jit RUNTESTFLAGS="-v -v -v"
+
+A summary of the tests can then be seen in:
+
+.. code-block:: console
+
+  jit/build/gcc/testsuite/jit/jit.sum
+
+and detailed logs in:
+
+.. code-block:: console
+
+  jit/build/gcc/testsuite/jit/jit.log
+
+The test executables can be seen as:
+
+.. code-block:: console
+
+  jit/build/gcc/testsuite/jit/*.exe
+
+which can be run independently.
+
+You can compile and run individual tests by passing "jit.exp=TESTNAME" to RUNTESTFLAGS e.g.:
+
+.. code-block:: console
+
+   [gcc] $ make check-jit RUNTESTFLAGS="-v -v -v jit.exp=test-factorial.c"
+
+and once a test has been compiled, you can debug it directly:
+
+.. code-block:: console
+
+   [gcc] $ PATH=.:$PATH \
+           LD_LIBRARY_PATH=. \
+           LIBRARY_PATH=. \
+             gdb --args \
+               testsuite/jit/test-factorial.exe
+
+Environment variables
+---------------------
+When running client code against a locally-built libgccjit, three
+environment variables need to be set up:
+
+.. envvar:: LD_LIBRARY_PATH
+
+   `libgccjit.so` is dynamically linked into client code, so if running
+   against a locally-built library, ``LD_LIBRARY_PATH`` needs to be set
+   up appropriately.  The library can be found within the "gcc"
+   subdirectory of the build tree:
+
+  .. code-block:: console
+
+    $ file libgccjit.so*
+    libgccjit.so:       symbolic link to `libgccjit.so.0'
+    libgccjit.so.0:     symbolic link to `libgccjit.so.0.0.1'
+    libgccjit.so.0.0.1: ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), dynamically linked, not stripped
+
+.. envvar:: PATH
+
+  The library uses a driver executable for converting from .s assembler
+  files to .so shared libraries.  Specifically, it looks for a name
+  expanded from
+  ``${target_noncanonical}-gcc-${gcc_BASEVER}${exeext}``
+  such as ``x86_64-unknown-linux-gnu-gcc-5.0.0``.
+
+  Hence ``PATH`` needs to include a directory where the library can
+  locate this executable.
+
+  The executable is normally installed to the installation bindir
+  (e.g. /usr/bin), but a copy is also created within the "gcc"
+  subdirectory of the build tree for running the testsuite, and for ease
+  of development.
+
+.. envvar:: LIBRARY_PATH
+
+  The driver executable invokes the linker, and the latter needs to locate
+  support libraries needed by the generated code, or you will see errors
+  like:
+
+  .. code-block:: console
+
+    ld: cannot find crtbeginS.o: No such file or directory
+    ld: cannot find -lgcc
+    ld: cannot find -lgcc_s
+
+  Hence if running directly from a locally-built copy (without installing),
+  ``LIBRARY_PATH`` needs to contain the "gcc" subdirectory of the build
+  tree.
+
+For example, to run a binary that uses the library against a non-installed
+build of the library in LIBGCCJIT_BUILD_DIR you need an invocation of the
+client code like this, to preprend the dir to each of the environment
+variables:
+
+.. code-block:: console
+
+  $ LD_LIBRARY_PATH=$(LIBGCCJIT_BUILD_DIR):$(LD_LIBRARY_PATH) \
+    PATH=$(LIBGCCJIT_BUILD_DIR):$(PATH) \
+    LIBRARY_PATH=$(LIBGCCJIT_BUILD_DIR):$(LIBRARY_PATH) \
+      ./jit-hello-world
+  hello world
+
+Overview of code structure
+--------------------------
+
+* ``libgccjit.c`` implements the API entrypoints.  It performs error
+  checking, then calls into classes of the gcc::jit::recording namespace
+  within ``jit-recording.c`` and ``jit-recording.h``.
+
+* The gcc::jit::recording classes (within ``jit-recording.c`` and
+  ``jit-recording.h``) record the API calls that are made:
+
+   .. literalinclude:: ../../jit-common.h
+    :start-after: /* Recording types.  */
+    :end-before: /* End of recording types. */
+    :language: c++
+
+* When the context is compiled, the gcc::jit::playback classes (within
+  ``jit-playback.c`` and ``jit-playback.h``) replay the API calls
+  within langhook:parse_file:
+
+   .. literalinclude:: ../../jit-common.h
+    :start-after: /* Playback types.  */
+    :end-before: /* End of playback types. */
+    :language: c++
+
+   .. literalinclude:: ../../notes.txt
+    :lines: 1-
+
+Here is a high-level summary from ``jit-common.h``:
+
+.. include:: ../../jit-common.h
+  :start-after: This comment is included by the docs.
+  :end-before: End of comment for inclusion in the docs.  */
-- 
1.8.5.3