llvm dev - Nov 2017 - Correctly linking against libLLVM (single shared library build)

On 11/14/2017, 01:26 AM, Chris Bieneman wrote:
> Sorry for the delayed response. I've been out of town a lot lately.
> 
> The documentation you referenced is unfortunately out of date (you might
notice it still references autoconf). I'll see if I can find time to update
it, but the guidance should be to use the `llvm_config` CMake function instead.
The proper usage of that in the example there would be to replace the call to
`llvm_map_components_to_libnames` with `llvm_config(simple-tool support core
irreader)`.
> 
> `llvm_config` should properly handle the LLVM shared library.
Actually it does not work at all. It behaves exactly the same as
map_components with this CMakeLists.txt:
cmake_minimum_required(VERSION 3.4.3)
project(SimpleProject)

find_package(LLVM REQUIRED CONFIG)

message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")

llvm_map_components_to_libnames(llvm_libs support core irreader)
message(STATUS "Components mapped to libnames: ${llvm_libs}")

add_executable(bubak a.c)

llvm_config(bubak support core irreader)
get_target_property(LL bubak LINK_LIBRARIES)
message(STATUS "Components mapped by llvm_config: ${LL}")


It results in:
-- Found LLVM 4.0.1
-- Using LLVMConfig.cmake in: /usr/lib64/cmake/llvm
-- Components mapped to libnames: LLVMSupport;LLVMCore;LLVMIRReader
-- Components mapped by llvm_config: LLVMSupport;LLVMCore;LLVMIRReader



And in turn we get linking errors:
 [ 50%] Linking C executable bubak
/usr/lib64/gcc/x86_64-suse-linux/7/../../../../x86_64-suse-linux/bin/ld:
cannot find -lLLVMSupport
/usr/lib64/gcc/x86_64-suse-linux/7/../../../../x86_64-suse-linux/bin/ld:
cannot find -lLLVMCore
/usr/lib64/gcc/x86_64-suse-linux/7/../../../../x86_64-suse-linux/bin/ld:
cannot find -lLLVMIRReader

So this does not work either :/.

thanks,
-- 
js
suse labs

On Thursday, 16 November 2017 08:34:50 CET Jiri Slaby
wrote:
> Actually it does not work at all. It behaves exactly the same as
> map_components with this CMakeLists.txt:
> llvm_config(bubak support core irreader)
I think the llvm_config needs USE_SHARED parameter, something like:
  llvm_config(bubak USE_SHARED support core irreader)

Otherwise it assumes you want to link with the static libraries.

In our case we do not package the static libraries, so it would make sense if 
llvm_config defaulted to USE_SHARED - we could patch it to behave that way in 
our package.

Michal Srb

On 11/16/2017, 08:45 AM, Michal Srb wrote:
> On Thursday, 16 November 2017 08:34:50 CET Jiri Slaby wrote:
>> Actually it does not work at all. It behaves exactly the same as
>> map_components with this CMakeLists.txt:
> 
>> llvm_config(bubak support core irreader)
> 
> I think the llvm_config needs USE_SHARED parameter, something like:
>   llvm_config(bubak USE_SHARED support core irreader)
> 
> Otherwise it assumes you want to link with the static libraries.
> 
> In our case we do not package the static libraries, so it would make sense
if
> llvm_config defaulted to USE_SHARED - we could patch it to behave that way
in
> our package.
That neither works for me, unfortunately:
-- Components mapped by llvm_config: LLVMSupport;LLVMCore;LLVMIRReader

So it's huge defunct mess :(. This all should be indeed handled by the
internals of llvm cmake files. And I believe this is exactly the reason
why klee by default invokes llvm-config *program* and not the
llvm-config (or other) cmake macro (one has to explicitly set
USE_CMAKE_FIND_PACKAGE_LLVM=ON to use the latter).

On the top of all that, trying to map the "native" component errors
the
cmake process with:
CMake Error at /usr/lib64/cmake/llvm/LLVM-Config.cmake:126 (message):
  Target X86 is not in the set of libraries.
Call Stack (most recent call first):
  /usr/lib64/cmake/llvm/LLVM-Config.cmake:66
(llvm_map_components_to_libnames)
  /usr/lib64/cmake/llvm/LLVM-Config.cmake:59 (explicit_llvm_config)
  CMakeLists.txt:19 (llvm_config)

With or without USE_SHARED, with llvm_map_components_to_libnames or
llvm_config.

This works, of course:
$ llvm-config --libnames native
libLLVM.so

thanks,
-- 
js
suse labs