[llvm-dev] (Thin)LTO llvm build

[Teresa Johnson via llvm-dev]

On Wed, Dec 21, 2016 at 9:00 AM, Carsten Mattner <carstenmattner at gmail.com>
wrote:

> On Wed, Dec 21, 2016 at 2:55 PM, Teresa Johnson <tejohnson at google.com>
> wrote:
> > I think you can get this via "ninja -t commands bin/lldb-argdumper"
> > (this will give you a lot of output, all of the compilation commands
> > used to build that target). Or redo the build with -v to be sure.
>
> Unfortunately the old build tree is gone for space reclaim reasons. Sorry,
> I'll make sure to not nuke it the next time. I guess I thought the detailed
> error message would be enough.
>
> I didn't build again, but I did configure with the settings posted
> yesterday,
> and there's a warning which I'm unsure how to interpret and if it's a
> concern:
>
> ---
> CMake Warning at tools/lldb/cmake/modules/LLDBConfig.cmake:409 (message):
>   You appear to be linking to libstdc++ version lesser than 4.9 without
>   exceptions enabled.  These versions of the library have an issue, which
>   causes occasional lldb crashes.  See
>   <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59656> for details.
> Possible
>   courses of action are:
>
>   - use libstdc++ version 4.9 or newer
>
>   - use libc++ (via LLVM_ENABLE_LIBCXX)
>
>   - enable exceptions (via LLVM_ENABLE_EH)
>
>   - ignore this warning and accept occasional instability
> Call Stack (most recent call first):
>   tools/lldb/CMakeLists.txt:4 (include)
> ---
>
> libstdc++ is 6.2.1 so the CMake check seems wrong.
>

Or maybe it is picking up a different libstdc++ from somewhere else on your
system? Here's the check from the cmake file:

    # There doesn't seem to be an easy way to check the library
version. Instead, we rely on the
    # fact that std::set did not have the allocator constructor
available until version 4.9
    check_cxx_source_compiles("
            #include <set>
            std::set<int> s = std::set<int>(std::allocator<int>());
            int main() { return 0; }"

LLDB_USING_LIBSTDCXX_4_9)

So the version check isn't precise, but unless libstdc++ 6.2.1 doesn't have
this interface available, which seems unlikely, something else is going
wrong.

Teresa


>
> This prompted me to use -libstd=libc++ and -DLLVM_ENABLE_LIBCXX=ON,
> but for some reason Arch Linux packages llvm and clang in version 3.9.0
> but libc++ in 3.8.0, so I skipped it.
>
> Unless the above libstdc++ warning is a problem, I will build and report
> back when done.
>



-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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