Update macOS build scripts for libomp dependency (#906)

* Link against checked in libomp.dylib

* Try another explicit link strategy

* Show contents of osx folder

* Try another linker strategy

* go back to old linker pattern

* try other syntax

* Try checked in openmp headers

* try getting more info from otool

* Try adapting libomp rpath on mac

* Ensure libomp lands in drops folder

* Additional copy of libomp

* Add explanatory comments

* Use @loader_path instead of @executable_path

Author: swernli

src/Simulation/Native/CMakeLists.txt

@@ -90,15 +90,21 @@ include_directories(${PROJECT_SOURCE_DIR}/src)
 if(ENABLE_OPENMP)
 
 if (APPLE)
-    set(OPENMP_PATH             "/usr/local/opt/libomp")
-    set(OPENMP_COMPILER_FLAGS   "-Xpreprocessor -fopenmp -I${OPENMP_PATH}/include -lomp -L${OPENMP_PATH}/lib")
+    set(OPENMP_LOCAL_PATH       "${PROJECT_SOURCE_DIR}/osx")
+    # Note we use `-rpath @loader_path` to ensure the produced binary includes the folder of the binary
+    # itself in the runtime search path for dynamic library load, regardless of environment settings.
+    # We don't use `@executable_path` because that takes into account recursive dependencies and will be
+    # the folder of the originally launched binary (root of the dependency tree) instead of loading binary
+    # (the immediate parent in the dependency tree), which will be the simulatory library itself.
+    # See https://www.man7.org/linux/man-pages/man1/ld.1.html and https://stackoverflow.com/questions/52981210/linking-with-dylib-library-from-the-command-line-using-clang
+    set(OPENMP_COMPILER_FLAGS   "-Xpreprocessor -fopenmp -I${OPENMP_LOCAL_PATH}/include -L${OPENMP_LOCAL_PATH} -lomp -rpath @loader_path")
     set(OPENMP_LIB_NAME         "omp")
 
     set(OpenMP_CXX_FLAGS        "${OPENMP_COMPILER_FLAGS}")
     set(OpenMP_C_FLAGS          "${OPENMP_COMPILER_FLAGS}")
     set(OpenMP_CXX_LIB_NAMES    "${OPENMP_LIB_NAME}")
     set(OpenMP_C_LIB_NAMES      "${OPENMP_LIB_NAME}")
-    set(OpenMP_omp_LIBRARY      "${OPENMP_PATH}/lib/libomp.dylib")
+    set(OpenMP_omp_LIBRARY      "${OPENMP_LOCAL_PATH}/libomp.dylib")
 endif()
 
 find_package(OpenMP)

src/Simulation/Native/build-native-simulator.ps1

@@ -3,6 +3,15 @@
 
 Write-Host "##[info]Build Native simulator for $Env:BUILD_CONFIGURATION"
 
+if ($IsMacOS) {
+    # To ensure loading succeeds on Mac the install id of the library needs to be updated to use 
+    # paths relative to target dynamic load path. Otherwise it will keep the full path encoding in the
+    # library from when it was built by homebrew.
+    # See https://stackoverflow.com/questions/52981210/linking-with-dylib-library-from-the-command-line-using-clang
+    Write-Host "##[info]Fixing binary dependencies with install_name_tool..."
+    install_name_tool -id "@rpath/libomp.dylib" (Join-Path $PSScriptRoot osx libomp.dylib)
+}
+
 
 $nativeBuild = (Join-Path $PSScriptRoot "build")
 if (-not (Test-Path $nativeBuild)) {
@@ -72,6 +81,12 @@ else {
 }
 cmake --build . --config "$Env:BUILD_CONFIGURATION" --target install
 
+if ($IsMacOS) {
+    Write-Host "##[info]Copying libomp..."
+    Copy-Item -Verbose (Join-Path $PSScriptRoot osx libomp.dylib) (Join-Path $PSScriptRoot build)
+    Copy-Item -Verbose (Join-Path $PSScriptRoot osx libomp.dylib) (Join-Path $PSScriptRoot build drop)
+}
+
 Pop-Location