[MacPorts] #51929: ld64-latest (and others?): default variant llvm38 breaks linking with pre-3.8-clang

[MacPorts]

#51929: ld64-latest (and others?): default variant llvm38 breaks linking with
pre-3.8-clang
---------------------+-------------------------
 Reporter:  ionic@…  |      Owner:  jeremyhu@…
     Type:  defect   |     Status:  new
 Priority:  Normal   |  Milestone:
Component:  ports    |    Version:
 Keywords:           |       Port:  ld64-latest
---------------------+-------------------------
 Recently, I changed my variants on `ld64-latest` and `cctools` from
 whatever I used before (probably `llvm33`) to the new default variant
 (`llvm38`) on OS X 10.9+ (with me being on 10.9.5.)

 While installing `clang-3.8` as a dependency of something else, I hit this
 error:

 {{{
 -- Check for working C compiler: /opt/local/bin/clang-mp-3.7 -- broken
 CMake Error at
 /opt/local/share/cmake-3.6/Modules/CMakeTestCCompiler.cmake:61 (message):
   The C compiler "/opt/local/bin/clang-mp-3.7" is not able to compile a
   simple test program.

   It fails with the following output:

    Change Dir:
 /opt/local/var/macports/build/_opt_local_var_macports_sources_macports.rsync.ionic.de_release_ports_lang_llvm-3.8/clang-3.8/work/build/CMakeFiles/CMakeTmp



   Run Build Command:"/usr/bin/make" "cmTC_b11b8/fast"

   /Applications/Xcode.app/Contents/Developer/usr/bin/make -f
   CMakeFiles/cmTC_b11b8.dir/build.make CMakeFiles/cmTC_b11b8.dir/build

   Building C object CMakeFiles/cmTC_b11b8.dir/testCCompiler.c.o

   /opt/local/bin/clang-mp-3.7 -pipe -Os -arch x86_64
   -mmacosx-version-min=10.9 -o CMakeFiles/cmTC_b11b8.dir/testCCompiler.c.o
 -c
 /opt/local/var/macports/build/_opt_local_var_macports_sources_macports.rsync.ionic.de_release_ports_lang_llvm-3.8/clang-3.8/work/build/CMakeFiles/CMakeTmp/testCCompiler.c


   Linking C executable cmTC_b11b8

   /opt/local/bin/cmake -E cmake_link_script
   CMakeFiles/cmTC_b11b8.dir/link.txt --verbose=1

   /opt/local/bin/clang-mp-3.7 -pipe -Os -arch x86_64
   -mmacosx-version-min=10.9 -Wl,-search_paths_first
   -Wl,-headerpad_max_install_names -L/opt/local/lib
   -Wl,-headerpad_max_install_names -Wl,-rpath, at loader_path
   -Wl,-rpath, at loader_path/ CMakeFiles/cmTC_b11b8.dir/testCCompiler.c.o -o
   cmTC_b11b8

   dyld: Library not loaded: @executable_path/../lib/libLTO.dylib

     Referenced from: /opt/local/libexec/llvm-3.7/bin/ld
     Reason: Incompatible library version: ld requires version 1.0.0 or
 later, but libLTO.dylib provides version 0.0.0

   clang: error: unable to execute command: Trace/BPT trap: 5

   clang: error: linker command failed due to signal (use -v to see
   invocation)
 }}}

 Further investigation revealed:

 {{{
 root at nopileos~# ls -ldh /opt/local/libexec/llvm-3.7/bin/ld
 lrwxr-xr-x 1 root 26 Jul 27 23:42 /opt/local/libexec/llvm-3.7/bin/ld ->
 /opt/local/libexec/ld64/ld
 }}}

 So when using clang-3.7, the system-default linker as installed by
 `ld64`/the other `ld64-version` ports are used, good.

 {{{
 root at nopileos~# otool -L /opt/local/libexec/llvm-3.7/lib/libLTO.dylib
 /opt/local/libexec/llvm-3.7/lib/libLTO.dylib:
         /opt/local/libexec/llvm-3.7/lib/libLTO.dylib (compatibility
 version 0.0.0, current version 0.0.0)
         /opt/local/libexec/llvm-3.7/lib/libLLVM-3.7.dylib (compatibility
 version 0.0.0, current version 0.0.0)
         [...]
 }}}

 `llvm-3.7`'s `libLTO` has compat version 0.0.0, current version 0.0.0.

 {{{
 root at nopileos~# otool -L /opt/local/libexec/llvm-3.8/lib/libLTO.dylib
 /opt/local/libexec/llvm-3.8/lib/libLTO.dylib:
         @rpath/libLTO.dylib (compatibility version 1.0.0, current version
 3.8.1)
         @rpath/libLLVM.dylib (compatibility version 1.0.0, current version
 3.8.1)
         [...]
 }}}

 `llvm-3.8`'s `libLTO` changed the compat version to 1.0.0 and the current
 version to 3.8.1.

 {{{
 root at nopileos~# otool -L /opt/local/libexec/ld64/ld
 /opt/local/libexec/ld64/ld:
         @executable_path/../lib/libLTO.dylib (compatibility version 1.0.0,
 current version 3.8.1)
         [...]
 }}}

 And the binary installed by `ld64-latest` (and symlinked via `ld64`) needs
 compat version 1.0.0.

 `clang-3.7` invokes `/opt/local/libexec/llvm-3.7/bin/ld`, so the expanded
 path to the library through `@executable_path` is
 `/opt/local/libexec/llvm-3.7/lib/libLTO.dylib`, which has (see above) a
 lower compat version of 0.0.0.

 Breakage.


 A fix might be to '''not''' use `@executable_path`, but rewrite the libLTO
 library dependency to always use the `libLTO` library as installed by the
 selected `llvm*`-variant version.

 I haven't looked at the source code and how difficult that would be,
 though.

-- 
Ticket URL: <https://trac.macports.org/ticket/51929>
MacPorts <https://www.macports.org/>
Ports system for OS X