Error while running configure "Cannot locate libclang or headers"

[Vipin Sharma]

Hi Jorn and Maurizio,

Your suggestions are helpful, I could solve this problem. Explained
analysis in detail here.

On Fri, Nov 20, 2020 at 8:18 PM Maurizio Cimadamore <
maurizio.cimadamore at oracle.com> wrote:

>
> On 20/11/2020 14:33, Jorn Vernee wrote:
> > Hi,
> >
> > AFAIK if you're building from sources you need to use the cmake
> > install target for it to produce a "package" that you can use I think
> > some headers might otherwise be missing.
> >
> >     cmake --build <build dir> --target install
> >
> > That will install at whatever CMAKE_INSTALL_PREFIX is set to
> > (recommend setting this explicitly, instead of using the default). You
> > can point the jdk build at that afterwards package.
> >
> > That said, using a binary distribution might be easier, since it
> > should already have the right directory structure.
>
> I wonder if (i) the binary distro you have tried is compatible with
> 19.10 - I remember trying out several available on the LLVM website few
> months ago, and none of them worked out of the box on Ubuntu 20.04
> (while many do on Ubuntu 18.04). Maybe 19.10 is in a similar boat



Executed the gcc test with pre-built binaries, below are observations:

command:
gcc -I/home/vipin/Softwares/clang+llvm-9.0.0-x86_64-pc-linux-gnu/include
-L/home/vipin/Softwares/clang+llvm-9.0.0-x86_64-pc-linux-gnu/lib
testClang.c -lclang

Output:
... (some undefined reference errors similar to below example)
/usr/bin/ld:
/home/vipin/Softwares/clang+llvm-9.0.0-x86_64-pc-linux-gnu/lib/libclang.so:
undefined reference to `Z3_solver_inc_ref'
collect2: error: ld returned 1 exit status

It fails probably because the clang binaries I am using are for Ubuntu
19.04 and I am using version 19.10, seems you are right binary distro I
have used may not be compatible.


>
> So it could be both the paths you tried fail, but for different reasons
> - as Jorn mentioned, the build you have might not be 100% ok - and the
> binary you downloaded might have dependencies that are not satisfied on
> your system.
>
> The gcc test I suggested in the previous email should help in narrowing
> this down - if you see compilation/linker issues there, then we know
> where to look.
>

This is command executed to test this
gcc -I/home/vipin/Softwares/llvm-project/build/include
-L/home/vipin/Softwares/llvm-project/build/lib testClang.c -lclang

console output:
testClang.c:1:10: fatal error: clang-c/Index.h: No such file or directory
    1 | #include "clang-c/Index.h"
      |          ^~~~~~~~~~~~~~~~~
compilation terminated.

I checked dir (clang build using source)
/home/vipin/Softwares/llvm-project/build/include/, below are its contents:

vipin:/home/vipin/Softwares/llvm-project/build/include$ ls -ltr
drwxr-xr-x 6 vipin vipin 4096 Nov 18 23:22 llvm

And contents for dir
/home/vipin/Softwares/clang+llvm-9.0.0-x86_64-pc-linux-gnu/include
(pre-built clang binaries) are:

vipin:/home/vipin/Softwares/clang+llvm-9.0.0-x86_64-pc-linux-gnu/include$
ls -ltr
llvm-c
llvm
c++
polly
clang-c
clang
lld

in pre-built binaries, I can see we have include/clang-c/Index.h, seems
that is because I needed to execute one more step to install clang, as Jorn
suggested.

I can confirm that this problem is resolved after using the below command
Jorn provided.
cmake --build /home/vipin/Softwares/llvm-project/build --target install

Just I could not use CMAKE_INSTALL_PREFIX properly so installation was done
in /usr/local/... directories.
And because clang is available at /usr/local/bin, I don't need to specify
the clang install path in the configure command using --with-libclang=


> Maurizio
>
> >
> > HTH,
> > Jorn
> >
> > On 20/11/2020 12:52, Maurizio Cimadamore wrote:
> >>
> >> On 19/11/2020 21:51, Vipin Sharma wrote:
> >>> dir: /home/vipin/Downloads/clang+llvm-9.0.0-x86_64-pc-linux-gnu
> >>> libexec
> >>> include
> >>> share
> >>> lib
> >>> bin
> >>
> >> This looks totally ok.
> >>
> >> Just one more test: can you run `clang` from there? Or do you get
> >> errors pointing at missing dependencies?
> >>
> >> This is really odd. I have basically the same setup (except for newer
> >> Ubuntu), I have built clang sources from scratch, then pointed the
> >> JDK build to the LLVM build folder and it all worked out.
> >>
> >> If all else fail, it would be nice to try and do what autoconf is
> >> trying to do, which is to compile a small program against libclang
> >> include/library and see if that works correctly. Something like:
> >>
> >> ```
> >> $ cat testClang.c
> >> #include "clang-c/Index.h"
> >>
> >> int main(void) {
> >>    clang_getClangVersion();
> >>    return 0;
> >> }
> >> ```
> >>
> >> Then try to compile it using gcc, and supply the "-I" (capital i)
> >> option to point at the LLVM include folder, "-L" to point at LLVM lib
> >> folder, and then "-l clang" (lower case "L") to set linker dependency
> >> on libclang.
> >>
> >> E.g - in my system:
> >>
> >> ```
> >> gcc -I/opt/clang/llvm-10/include -L/opt/clang/llvm-10/lib testClang.c
> >> -lclang
> >> ```
> >>
> >> If you get compilation errors, or linker errors, then there's
> >> something up with the environment. AFAIK, autoconf does something
> >> like that to "check that libclang is really there".
> >>
> >> Maurizio
> >>
> >>
> >>
> >>
>

Thanks,
Vipin