[cfe-dev] libclang shared library that exports all symbols

[via cfe-dev]

Here's my edited comment from the differential review, I think it's a great 
idea but there are fundamental flaws and inconsistency with it:


I'm in support as long as it's a configuration option defaulting similar to
LLVM's one. Should likely follow the same naming convention as LLVM, ie. clang-
shlib. Clang has a lot of tools it ships with especially if you consider extras,
I think this is one of the cases where an exception for libClang-8.so can be
made as long as it's not a default. It would make builds of things like clang-
tidy much faster without requiring a fully shared library build.

IIRC libclang is a tool in itself, and is not mandatory for Clang driver tool
build which is the most fundamental part to most customers, while this new
library is not. There are a lot of things the downstream discussions have not
covered it seems since this only accounts for for a full
Clang+Tools+ARCMT+StaticAnalyzer+Extra (ie. tidy, include fixer) build. This
just fails to account for so much. The pairing of libclang and the new shared
library defeats the entire point of it altogether, since libclang is not
required by the driver. Nor by most in-tree tools.


On 12/09/2018 at 6:57 PM, "Pirama Arumuga Nainar via cfe-dev" <cfe-dev at lists.llvm.org> wrote:
>
>Hi Ivan,
>
>Thanks for pointing out Clang plugins as a viable alternative for 
>my
>proposal.  We had considered writing the tools as a plugin but 
>decided
>against it - due to some rough edges with Android's build system.
>
>For now, we decided to carry build rules for the proposed library 
>in
>downstream.  I've updated my change 
>(https://reviews.llvm.org/D50359) to
>make it more general, and will leave it open in case there's more 
>interest
>to revive it in the future.
>
>Thanks,
>-Pirama
>
>On Mon, Aug 6, 2018 at 11:28 PM Ivan Donchevskii 
><ivan.donchevskii at qt.io>
>wrote:
>
>> Hi!
>>
>> I think I meant CLANG_PLUGIN_SUPPORT flag which enables
>> export_executable_symbols(clang) in
>> tools\clang\tools\driver\CMakeLists.txt
>>
>> Probably in combination with LLVM_EXPORT_SYMBOLS_FOR_PLUGINS.
>>
>>
>> Ivan
>> ------------------------------
>> *From:* Pirama Arumuga Nainar <pirama at google.com>
>> *Sent:* Monday, August 6, 2018 10:53:29 PM
>> *To:* Ivan Donchevskii; cfe-dev list
>> *Cc:* Tzu-hsiang Chien; Stephen Hines
>> *Subject:* Re: [cfe-dev] libclang shared library that exports 
>all symbols
>>
>>
>>
>> On Fri, Aug 3, 2018 at 1:37 AM Ivan Donchevskii 
><ivan.donchevskii at qt.io>
>> wrote:
>>
>> Hi!
>> Why do you need to mix C++ symbols with what libclang exports?
>>
>>
>> My reasoning was that the C/C++ difference was already imposed 
>by the
>> headers included by a libclang.so user.  But I also see why 
>limiting the
>> exported symbols can catch user errors.
>>
>>
>> Doesn't it make sense to have separate clang.so instead? I also 
>think
>> there's already a possibility to build such library by providing 
>some LLVM
>> flags.
>>
>>
>> I think you mean LLVM_ENABLE_SHARED?  That builds each 
>individual library
>> (libclangAST, libclangDriver etc) as shared libraries, rather 
>than
>> producing a single shared library.  I am not aware of any other 
>option that
>> can help.
>>
>> To clarify my proposal, I've uploaded a patch (
>> https://reviews.llvm.org/D50359) that adds this new library.  
>The library
>> is named libclang-cxx in that patch - which I think is slightly 
>more
>> informative than libclang-full.
>>
>> Please add comments in the patch or to this discussions.
>>
>>
>> Kind regards,
>>
>> Ivan
>> ------------------------------
>> *From:* cfe-dev <cfe-dev-bounces at lists.llvm.org> on behalf of 
>Pirama
>> Arumuga Nainar via cfe-dev <cfe-dev at lists.llvm.org>
>> *Sent:* Thursday, August 2, 2018 11:48:16 PM
>> *To:* cfe-dev list
>> *Cc:* Tzu-hsiang Chien
>> *Subject:* Re: [cfe-dev] libclang shared library that exports 
>all symbols
>>
>> Ping for any thoughts on this proposal...
>>
>> On Thu, Jul 26, 2018 at 3:59 PM Pirama Arumuga Nainar 
><pirama at google.com>
>> wrote:
>>
>> libclang.so exports only the symbols needed by the C API.  This 
>is in
>> contrast to libLLVM.so that exports all symbols from the LLVM 
>static
>> libraries.  Would it be useful to provide a libclang shared 
>library that
>> exports all symbols for use by tools that use Clang's (admittedly
>> non-backwards-compatible) C++ API?
>>
>> We can either:
>> 1. Add a new shared library (libclang_full.so?) that is built 
>based on a
>> CMake option.
>> 2. Export all symbols from the current libclang.so.  We'd have 
>to also
>> include a few additional libraries such as libClangAnalysis.  
>Tools using
>> the C API are still restricted to the stable interface if they 
>use the
>> clang-c headers.
>>
>> Motivation:
>> There are a few Clang-based tools used by Android's build system 
>(1, 2)
>> that use the C++ API.  They are built using Android build rules 
>but need to
>> link against Android's Clang toolchain that's built with CMake.  
>We don't
>> want to include the libclang static libraries with the toolchain 
>for space
>> considerations, and also to avoid exposing Clang's build 
>internals
>> (internal library dependences and changes to them) to downstream 
>tools.
>>
>> Do other Clang/LLVM toolchain maintainers face similar issues 
>and have
>> solutions that are applicable here?
>>
>> [1]
>> 
>https://android.googlesource.com/platform/development/+/master/vndk
>/tools/header-checker/
>> [2]
>> 
>https://android.googlesource.com/platform/development/+/master/vndk
>/tools/vtable-dumper/
>>
>>