llvm dev - Mar 2012 - [LLVMdev] llvm-config --cxxflags does not give the result the configuration script wants?

Hello LLVM-DEV!

Recently I think I found a bug in llvm's CMakeLists.(I use llvm 3.1svn and
Clang 3.1) I follow the normal way to try to compile an application that
utilize both clang and llvm: I ./autogen.sh it, ./configure it and make it.
But the make fails. At last I found out the failure is because that the
Makefile's CXXFLAGS does not contain -fno-rtti option which is needed by
the compilation.

The "configure" file of the application use llvm-config --cxxflags to
assign to the CXXFLAGS. But Although I see that, under my platform, almost
all the the files inside LLVM and Clang are compiled with -fno-rtti, the
llvm-config --cxxflags does not give the correct flags that those files are
compiled. The following are something I thought is valuable to mention here:

As I probe the CMAKE_CXX_FLAGS of some of the CMakeLists.txt, I found there
is a "baseline" of this variable, mine is "-fPIC
-fvisibility-inlines-hidden". It means, no matter how a single
CMakeLists.txt changes CMAKE_CXX_FLAGS, it will remain the same when it
goes into another CMakeLists.txt.

Inside the llvm-config's source folder, the CMakeLists.txt shows how its
--cxxflags is set:
set(CXX_FLGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${uppercase_
CMAKE_BUILD_TYPE}} ${LLVM_DEFINITIONS}")
...
COMMAND echo s!@LLVM_CXXFLAGS@!${CXX_FLGS}! >> ${SEDSCRIPT_OBJPATH}

and my LLVM_DEFINITIONS is:

 -D_GNU_SOURCE -Wall -W -Wno-unused-parameter -Wwrite-strings -pedantic
-Wno-long-long -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS
-D__STDC_LIMIT_MACROS

I also use "make VERBOSE=1" to check how llvm and clang is compiled. I
see
clearly that they are both compiled with -fno-rtti.

So, at least under my system, when using cmake to configure the project, no
matter how the files are compiled, llvm-config --cxxflags will be the same.
It is:  -fPIC -fvisibility-inlines-hidden   -D_GNU_SOURCE -Wall -W
-Wno-unused-parameter -Wwrite-strings -pedantic -Wno-long-long
-D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS. It
is determined by the "baseline" of CMAKE_CXX_FLAGS and
LLVM_DEFINITIONS.

Is this probably a problem?
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20120313/f4434bf7/attachment.html>

Jun-qi Deng <dengjunqi06323011 at gmail.com> writes:
> Recently I think I found a bug in llvm's CMakeLists.(I use llvm 3.1svn
and
> Clang 3.1) I follow the normal way to try to compile an application that
> utilize both clang and llvm: I ./autogen.sh it, ./configure it and make it.
> But the make fails. At last I found out the failure is because that the
> Makefile's CXXFLAGS does not contain -fno-rtti option which is needed
by
> the compilation.
Is it? In my experience, it isn't. Please show the relevant command
generated by your makefile and the associated error message(s).

RTTI is an on/off option that changes per LLVM library, so setting
-fno-rtti for using LLVM makes no sense. VMCore and Support have -frtti
while most of the rest have -fno-rtti. The switch is decided on
cmake/modules/LLVMProcessSources.cmake depending on the value of
LLVM_REQUIRES_RTTI.

[snip]

> > Recently I think I found a bug in llvm's CMakeLists.(I use llvm
3.1svn
> and
> > Clang 3.1) I follow the normal way to try to compile an application
that
> > utilize both clang and llvm: I ./autogen.sh it, ./configure it and
make
> it.
> > But the make fails. At last I found out the failure is because that
the
> > Makefile's CXXFLAGS does not contain -fno-rtti option which is
needed by
> > the compilation.
>
> Is it? In my experience, it isn't. Please show the relevant command
> generated by your makefile and the associated error message(s).
>
> RTTI is an on/off option that changes per LLVM library, so setting
> -fno-rtti for using LLVM makes no sense. VMCore and Support have -frtti
> while most of the rest have -fno-rtti. The switch is decided on
> cmake/modules/LLVMProcessSources.cmake depending on the value of
> LLVM_REQUIRES_RTTI.
>
>
> Hello! I'm sorry, because I've already solved the build problem
with the
mentioned app manually, now it's not very convenient for me to reproduce
the error for the moment. I agree that "RTTI is an on/off option". But
I
think the point of the problem I mentioned here is: some applications that
depend on llvm and clang use llvm-config to configure their Makefile, while
the llvm-config cannot provide the correct information they need. And this
is what actually happened under my platform.

Regards,
TangKK
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20120314/20d10cbf/attachment.html>