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

[John Thompson]

Thanks for the reply, Doug.
> I think we need to understand what's going on here, first. Making it
possible to build plugins on Windows is an important aspect of this work,
and we'd like to be sure that we got it right before we go and annotate the
whole code-base.

I'll look further into caveats #1 (.inc dependency), #2 (Index tests), and
#5 (registry mechanism exporting).

Question:  If the Index stuff is put into the big DLL, that makes libclang
redundant, or means the big DLL is the new libclang (but with all the other
stuff exported too), doesn't it?  Or is there a reason to keep Index out of
the big DLL?

If my registry replacement mechanism is acceptible, #5 is probably not
needed.  But it's probably just finding the right definition inside the
registry classes to export, though it might be possible that non-public
accessiblity might prevent the export.  But I'll look into it further.

-John
On Mon, May 9, 2011 at 11:45 AM, Douglas Gregor <dgregor at apple.com> wrote:

>
>   On May 4, 2011, at 6:06 PM, John Thompson wrote:
>
>  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.
>
>
> This is all CMake stuff, which sounds okay in principle. Óscar is more
> qualified to review these changes than the rest of us.
>
>  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.
>
>
> Ugh. Alas, I've never seen another solution that actually works properly on
> Windows, so I can live with dllimport/dllexport scattered everywhere.
> Someone is going to have to be vigilant to ensure that these new _LINKAGE
> macros get added to new classes and functions as they go into the source
> base, since the vast majority of current LLVM and Clang developers won't be
> using LLVM/Clang in this way.
>
>  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.
>
>
> The Index tests are based on the libclang DLL, which itself is a standalone
> DLL containing most of Clang (without code-generation).
>
>  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).
>
>
> I think we need to understand what's going on here, first. Making it
> possible to build plugins on Windows is an important aspect of this work,
> and we'd like to be sure that we got it right before we go and annotate the
> whole code-base.
>
>  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.
>
>
> Okay.
>
> In general, I'm in favor of moving forward on this. However, this kind of
> architectural thing is Chris's domain, so I'd like to hear from him.
>
> - Doug
>



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