View Full Version : Problem using LLVM with Qt 5.0.0 within on Ubuntu

24th January 2013, 15:56

I use LLVM (3.2) in my project (Qt 5.0.0) and it works as expected on Windows and OS X, but on Ubuntu it just crashes. If I start my application, don't use any of the LLVM-specific stuff in my application, and try to quit my application, then I get the following debug traces:

0 __memmove_ssse3 memcpy-ssse3.S 1682 0x1348f8c
1 llvm::PassRegistry::removeRegistrationListener(llv m::PassRegistrationListener*) /usr/lib/i386-linux-gnu/libLLVM-3.0.so.1 0xb0278ddb
2 llvm::PassRegistrationListener::~PassRegistrationL istener() /usr/lib/i386-linux-gnu/libLLVM-3.0.so.1 0xb026aa06
3 llvm::PassNameParser::~PassNameParser() /usr/lib/i386-linux-gnu/libLLVM-3.0.so.1 0xb026aca2
4 llvm::cl::list<llvm::PassInfo const*, bool, llvm::PassNameParser>::~list() /home/me/myApp/build/plugins/myApp/libLLVM.so 0xb31eb8a4
5 __run_exit_handlers exit.c 78 0x1242f51
6 __GI_exit exit.c 100 0x1242fdd
7 __libc_start_main libc-start.c 258 0x12294db
8 _start 0x8068ca1

If you look at line 4, my application uses my version of LLVM (which I build as a Qt plugin), but then at lines 1, 2 and 3, we can see that my application somehow decided to use the system version of LLVM. Why is that? I have no idea!

All I know is that it used to work perfectly fine using Qt 4.8.x. I thought for a moment that it might be related to OpenGL/3D (Qt 5.0.0 uses OpenGL no matter what now, right?), especially since my Ubuntu box is in fact a virtual machine with no 3D acceleration (i.e. Mesa would take over and use llvmpipe?), but I then tried using the Ubuntu live CD (with 3D acceleration), and I got the same result, so I am puzzled...

Otherwise, if I manually rename the system version of LLVM (so that my application cannot 'see' it), then everything works as expected (i.e. no crash) but I obviously don't want and, in fact, can't really do that!

FWIW, here is another trace I get when starting my application and then trying to do some LLVM-specific stuff in my application:

0 llvm::FoldingSetNodeID::AddPointer(void const*) /usr/lib/i386-linux-gnu/libLLVM-3.0.so.1 0xb074f37a
1 clang::FunctionProtoType::Profile(llvm::FoldingSet NodeID&, clang::QualType, clang::QualType const*, unsigned int, clang::FunctionProtoType::ExtProtoInfo const&, clang::ASTContext const&) /home/me/myApp/build/libLLVM.so 0x43a6b2e
2 clang::FunctionProtoType::Profile(llvm::FoldingSet NodeID&, clang::ASTContext const&) /home/me/myApp/build/libLLVM.so 0x43a6dd4
3 llvm::ContextualFoldingSet<clang::FunctionProtoType, clang::ASTContext&>::NodeEquals(llvm::FoldingSetImpl::Node*, llvm::FoldingSetNodeID const&, unsigned int, llvm::FoldingSetNodeID&) const /home/me/myApp/build/libLLVM.so 0x427d59f
4 llvm::FoldingSetImpl::FindNodeOrInsertPos(llvm::Fo ldingSetNodeID const&, void*&) /usr/lib/i386-linux-gnu/libLLVM-3.0.so.1 0xb074fb67
5 clang::ASTContext::getFunctionType(clang::QualType , clang::QualType const*, unsigned int, clang::FunctionProtoType::ExtProtoInfo const&) const /home/me/myApp/build/libLLVM.so 0x426ecbb
6 clang::ASTContext::GetBuiltinType(unsigned int, clang::ASTContext::GetBuiltinTypeError&, unsigned int*) const /home/me/myApp/build/libLLVM.so 0x4274243
7 clang::Sema::LazilyCreateBuiltin(clang::Identifier Info*, unsigned int, clang::Scope*, bool, clang::SourceLocation) /home/me/myApp/build/libLLVM.so 0x48baa24
8 ?? /home/me/myApp/build/libLLVM.so 0x49fde04
9 clang::Sema::LookupName(clang::LookupResult&, clang::Scope*, bool) /home/me/myApp/build/libLLVM.so 0x4a03d13
10 clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>) /home/me/myApp/build/libLLVM.so 0x48cb270
11 clang::Sema::ActOnDeclarator(clang::Scope*, clang::Declarator&) /home/me/myApp/build/libLLVM.so 0x48cb8f3
12 clang::Parser::ParseDeclarationAfterDeclaratorAndA ttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&) /home/me/myApp/build/libLLVM.so 0x47196e1
13 clang::Parser::ParseDeclGroup(clang::ParsingDeclSp ec&, unsigned int, bool, clang::SourceLocation*, clang::Parser::ForRangeInit*) /home/me/myApp/build/libLLVM.so 0x4725883
14 clang::Parser::ParseDeclOrFunctionDefInternal(clan g::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec&, clang::AccessSpecifier) /home/me/myApp/build/libLLVM.so 0x477563f
15 clang::Parser::ParseDeclarationOrFunctionDefinitio n(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*, clang::AccessSpecifier) /home/me/myApp/build/libLLVM.so 0x4775d79
16 clang::Parser::ParseExternalDeclaration(clang::Par ser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) /home/me/myApp/build/libLLVM.so 0x4779c77
17 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&) /home/me/myApp/build/libLLVM.so 0x4779f48
18 clang::ParseAST(clang::Sema&, bool, bool) /home/me/myApp/build/libLLVM.so 0x470e49c
19 clang::ASTFrontendAction::ExecuteAction() /home/me/myApp/build/libLLVM.so 0x4671a57
20 clang::CodeGenAction::ExecuteAction() /home/me/myApp/build/libLLVM.so 0x456db42
... <More>

Again, you can see that sometimes my application uses its version of LLVM while, at other times, it uses the system version of LLVM...!?

Now, I wouldn't expect many people to use LLVM in their project, but... how would you go about handling the case where your application uses its version of a library which is also used by your Linux system?...

Cheers, Alan.

30th January 2013, 11:58
Nobody, really?...

30th January 2013, 17:18
Ok, I have spent some time googling around and... I have found some kind of a solution to my problem. I guess I should have mentioned that my Ubuntu box is, in fact, an Ubuntu virtual machine running within VirtualBox, and... since Qt 5 now requires OpenGL for any kind of application, well... that can cause problems depending on what you do and it certainly causes problems in my case (because of my use of LLVM). Anyway, the 'solution' consists of using indirect rendering, e.g.


Really not ideal, but at least it's now working fine. (Seriously, why on earth does Qt 5 forces you to use OpenGL in an application which doesn't actually make use of it?!)