[llvm-dev] (Thin)LTO llvm build

[Mehdi Amini via llvm-dev]

> On Sep 16, 2016, at 2:27 PM, Mehdi Amini via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
>> 
>> On Sep 16, 2016, at 2:18 PM, Carsten Mattner <carstenmattner at gmail.com> wrote:
>> 
>> On Fri, Sep 16, 2016 at 10:54 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>> 
>>> Can you look for the specific errors in the CMake log and error files?
>>> 
>>> CMake is very good at not presenting the real issue…
>>> Here it is trying to build very simple programs to check features
>>> availability. Like:
>>> 
>>>  #include <strings.h>
>>>  int main() { ffs(0); return 0; }
>> 
>> In CMakeError.log there are errors like:
>> 
>> CheckIncludeFile.c:1:10: fatal error: 'malloc/malloc.h' file not found
>> #include <malloc/malloc.h>
>> 
>> ...
>> 
>> CheckIncludeFile.c:1:10: fatal error: 'ndir.h' file not found
>> #include <ndir.h>
>> 
>> ...
>> 
>> CheckIncludeFile.c:1:10: fatal error: 'sys/ndir.h' file not found
>> #include <sys/ndir.h>
>> 
>> ...
>> 
>> fatal error: 'intrin.h' file not found
>> 
>> These seem like tests that are expected to fail.
>> 
>> ...
>> 
>> The interesting test
>> 
>> int main() { __builtin_ffs(0); return 0; }
>> 
>> fails like this:
>> 
>> /usr/bin/ld[...]llvm/bin/../lib/LLVMgold.so:
>> cannot open shared object file: No such file[…]
> 
> 
> I assume that "/usr/bin/ld[...]llvm/bin” is the path where clang is installed right?
> It seems that when you built the stage1 clang, it didn’t find Gold installed, and then didn’t build the plugin.
> So you need to go back to the first build (not the ThinLTO one, the one with the system compiler), and make sure that CMake finds gold.

You probably missed -DLLVM_BINUTILS_INCDIR.

See: http://llvm.org/docs/GoldPlugin.html

— 
Mehdi


> 
> 
>> 
>> I have two questions here:
>> 
>> Is there anything I might have missed when configuring the gcc-built
>> llvm install for it to be incomplete in the linker department? I mean,
>> the system linker is used (not lld) and that via CC=clang is looking
>> for the gold linker plugin, which seems to be missing. Probably
>> something got lost in my transition from autoconf to cmake?
>> 
>> Anything else to pass to cmake so that it, in addition to llvm-ar and
>> llvm-ranlib, also used lld? Or isn't that a requirement for building
>> with ThinLTO?
> 
> No requirement for lld.
> 
> 
> — 
> Mehdi
> 
> 
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