[cfe-dev] Big Clang DLL, plug-in mechanism revision

[John Thompson]

Hi,

May I solicit some feedback on the work I've done for these two issues?

Basically I'm attacking the problem from two separate angles, doing the
following changes in two separate trees.

In one, I revised the plug-in mechanism, dumbing it down a bit, to avoid the
problems encountered on Windows where the plug-in registry referenced in the
plug-in DLL doesn't connect with the plug-in registry in the clang
executable.  I say dumbing it down a bit because it uses a more basic vector
of structures for storing the plugin name and a callback function for
creating the action node.  The original patch was kind of old, so I updated
it, using one new file from the other tree for the __cdeclspec(dllexport)
wrapper.  Note that I left in the original plug-in registry stuff
side-by-side.  I tested it the earlier version on both Windows and Linux.
It still has the potential problem of the plug-in not having access to
everything in the clang executable, which can only be resolved by using a
big Clang DLL.  Here's the patches for this change:

http://www.jtlanguage.com/xfer/plugin_llvm_patch.txt
http://www.jtlanguage.com/xfer/plugin_clang_patch.txt

In the other, I did the ground work for creating a big Clang DLL from all
the LLVM and Clang sources used in the original Clang executable.  It
currently only exports a small subset of the functions, mostly only those
needed to get the Clang and other executables to link correctly.  I'll recap
the scheme later in this email, revising and pasting info from my original
messages, with some updates.  The clang.exe executable links and runs,
though there is some dependency problem I don't understand yet when doing
the "ALL_BUILD".  In running the tests, some of the Index tests fail for
unknown reasons.  Otherwise, without the cmake "LLVM_BUILD_DLL" option, the
normal build and test results are unchanged.  Yesterday I tested the patch
on Linux and fixed a couple of compile problems.  Basically, this shows that
the basic big DLL mechanism works, and that all that is needed is to add the
rest of the "*_LINKAGE" tags and fix the dependency and Index test
problems.  Here's the patches for this change:

http://www.jtlanguage.com/xfer/dll_llvm_patch.txt
http://www.jtlanguage.com/xfer/dll_clang_patch.txt

Note that the big Clang DLL does not automatically fix the original problem
of the plug-in registry, as the needed internal registry symbols are not
exported.  So the full solution of fixing the plug-in registry mechanism
probably requires both of these changes, the first for the registering
mechanism, and the second for allowing the plug-in to full access of the
Clang code and data.

Basically I'm looking for feedback on these two schemes, or a go-ahead with
checking in what I have so far, for a staged adoption.  Because the DLL
scheme still needs a lot of work in adding the "*_LINKAGE" tags to so many
declarations, I want to find out if the owners of the respective systems
approve of these changes, rather than continuing with all the work and
finding that it will not be used.  I know it's a pretty big change, and
Windows-specific, but I think it's important enough to try.

I'm thinking I could check in what I have at present (with any changes
required), which has the build changes and the new module-common headers,
and the subset of "*_LINKAGE" tag additions that let the link succeed, and
then check in the remaining changes in smaller batches, as I add the
remaining "*_LINKAGE" tags.

I'm not sure how the big Clang DLL fits into the long-term scheme of things,
whether it remains a special build option on Windows, or becomes the
mainstream version.  For now just leave it as a special build option.  I'm
also not sure if any other LLVM modules should be in the DLL, and whether
there should also be a separate LLVM DLL.  I started doing a little work on
this, but didn't include it here.

So here's stuff from the original email for the DLL stuff revisions, as I
missed a description of something I did on the LLVM side in the cmake files,
and I hadn't gotten the unit test mechanism to work at all.  Sorry for the
verbosity; I'm just trying to be complete:

The scheme is meant to satisfy the following design goals/constraints:
1. Create a single Windows DLL including the main Clang and LLVM modules
needed for a compiler and other tools, such that it's the only module you
need to link against (from the Clang/LLVM project).
2. Preserve the current module organization and build, leaving the
static-library and other platform's shared library versions as they are.
(This leaves open the option of creating per-module Windows DLLS in the
future.)
3. Enable Clang plug-ins to share the code and data space with the Clang or
other tool executables.
4. Make the "big" DLL version optional by means of cmake arguments given
upon running cmake. (I'm not sure of the criteria for deciding whether to
make it the default for Windows or not.)
These are the build changes, with respect to the cmake build tool:
1. A "BUILD_LLVM_DLL" configuration flag is added to the cmake build, such
that specifying "-DBUILD_LLVM_DLL=ON" in the cmake command line will enable
the big-DLL build. By default it is off.
2. Factor out the common portions of the "add_clang_library" into
"add_clang_library_common".

3. Modify the cmake macro "add_clang_library" to collect the source file
full path strings in a new target property.

4. Add a new "add_clang_dll" cmake macro for creating the big DLL. This
macro operates like "add_clang_library", but always builds a DLL target, and
doesn't collect the source paths. It also passes "LLVM_USE_DLL" and
"LLVM_EXPORTS" defines to the compiler, to enable the symbol exports to be
described later.
5. Create a new "ClangDLL" project under tools/clang/lib for creating the
big DLL, which uses the new "add_clang_dll" macro.
6. Add new "set_clang_components" and "set_clang_llvm_components" cmake
macros for use in conjunction with "add_clang_executable" to collect the
Clang and LLVM components, as opposed to setting "LLVM_USED_LIBS" and
"LLVM_LINK_COMPONENTS" directory. (These macros will substitute the big DLL
for the component libraries.)
7. Modify "add_clang_executable" to pass an "LLVM_USE_DLL" define to the
compiler if the big-DLL version is enabled. This define enables the symbol
imports/exports to be described later.

8. (new) Do similar changes to the LLVM-side cmake macros, such as chaning
add_llvm_library to collect the sources.
9. Update the clang executable, interpreter, and PrintFunctionNames projects
to use the new and revised cmake macros.
The source changes mainly consist of adding "(moduleNameUppercase)_LINKAGE"
macro instances to the declarations of the classes, functions, and other
symbols to be exported/imported, and new header files that define these
macros. These changes can be summarized as follows:
1. A new "(moduleName)Common.h" file is added to each LLVM and Clang module
include directory. This file defines a "(moduleNameUppercase)_LINKAGE" macro
for that component module. This macro expands to nothing for the non-big-DLL
version ("LLVM_USE_DLL" is not defined to the compiler), or to the
LLVM_EXPORT macro when building the DLL ("Clang_EXPORTS" or "LLVM_EXPORTS"
or "(moduleName)_EXPORTS" is defined), or to the LLVM_IMPORT macro when
building against the DLL ("LLVM_USE_DLL" is defined). This include file will
be included by any headers in the component needing the
"(moduleNameUppercase)_LINKAGE" macro.
2. A new "LLVMCommon.h" file is added to the include/llvm directory under
the root to define "LLVM_EXPORT" and "LLVM_IMPORT" macros that wrap the
Visual C++ "__declspec(dllexport)" and "__declspec(dllimport)" directives,
as well as to define the "LLVMCORE_LINKAGE" macro. This file will be
included by all the "(moduleName)Common.h" files for the LLVM components.
3. A new "ClangCommon.h" file is added to the tools/clang/include/clang
directory. It just includes the "LLVMCommon.h" file, and will be included by
the "(moduleName)Common.h" files for the Clang components.
In my experimental version, I added most of the "(moduleName)Common.h"
files, but I only added the "(moduleNameUppercase)_LINKAGE" macro instance
to some of the symbols, at least the ones needed by the Clang driver and
interpreter to link.
Caveats:
1. The ALL_BUILD project build breaks on some missing .inc files from the
X86 target project. I think this has to do with an inherent dependency
problem in the cmake build. Even though the "(target)CodeGenTable_gen"
project dependency is added to the DLL, the .inc files are not created
before the DLL link. I will look into this. A rebuild of the "clang" project
does work, as that was the focus of my experiment. The interpreter might
build too, as it did earlier.
2. Several of the "Index" tests don't pass.  I haven't figured out why yet.
3. As I mentioned, I only exported some of the symbols, those needed to get
the clang executables to build. A big edit (manual or automated) will be
needed to add the "(moduleNameUppercase)_LINKAGE" macros to the rest of the
symbols, and any needed "(moduleName)Common.h" headers not yet created.
4. I only enabled the X86 target in LLVM (the default for the Windows build
in general), for the purpose of this experiment. The other targets will need
to be done as well.
5. I tried running the PrintFunctionNames plugin, but there's still a
disconnect between the registry referenced by the plugin and the one in the
big DLL. I didn't look into it deep enough yet, but I'm guessing it has
something to do with the template mechanism used not being exported. I'm not
even sure how to export it. But I think the better solution is to switch to
the simplified plugin mechanism I provided a patch for in a previous post
(and which I'm still waiting for a review fornudge-nudge).
6. In building on Windows with the big DLL mechanism enabled, there are a
lot of "class 'someTemplateClass<_Ty>' needs to have dll-interface to be
used by clients of class 'someClass'" warnings. These just need to have some
extra template specialization declarations with the "*_LINKAGE" tag.

You can search on "CMakeLists.txt" and ".cmake" to see the cmake file
changes, or "Common.h" to see the new headers. Most of the rest of the
changes are just the adding of the "(moduleNameUppercase)_LINKAGE" macros to
the class and function definitions.

Thanks!

-John

-- 
John Thompson
John.Thompson.JTSoftware at gmail.com
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