[PATCH] D25568: [libcxx] [cmake] Use -print-libgcc-file-name option to find compiler runtime

[Michał Górny via cfe-commits]

mgorny created this revision.
mgorny added a reviewer: EricWF.
mgorny added a subscriber: cfe-commits.
Herald added subscribers: modocache, beanz.

Use the -print-libgcc-file-name compiler option to obtain the path to
libgcc or an equivalent compiler runtime library, rather than hardcoding
-lgcc_s. This aims to make it possible to avoid linking with -lgcc_s
when -rtlib=compiler-rt is used along with libunwind.


https://reviews.llvm.org/D25568

Files:
  cmake/Modules/HandleLibcxxFlags.cmake
  lib/CMakeLists.txt


Index: lib/CMakeLists.txt
===================================================================
--- lib/CMakeLists.txt
+++ lib/CMakeLists.txt
@@ -83,7 +83,7 @@
 add_library_flags_if(LIBCXX_HAS_C_LIB c)
 add_library_flags_if(LIBCXX_HAS_M_LIB m)
 add_library_flags_if(LIBCXX_HAS_RT_LIB rt)
-add_library_flags_if(LIBCXX_HAS_GCC_S_LIB gcc_s)
+add_libgcc_library()
 add_library_flags_if(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB atomic)
 
 # Add the unwinder library.
@@ -95,6 +95,8 @@
   else()
     add_interface_library(unwind)
   endif()
+else()
+  add_library_flags_if(LIBCXX_HAS_GCC_S_LIB gcc_s)
 endif()
 
 # Setup flags.
Index: cmake/Modules/HandleLibcxxFlags.cmake
===================================================================
--- cmake/Modules/HandleLibcxxFlags.cmake
+++ cmake/Modules/HandleLibcxxFlags.cmake
@@ -196,6 +196,29 @@
   endforeach()
 endmacro()
 
+# Attempt to detect the correct compiler runtime library and add it
+# to 'LIBCXX_LIBRARIES'. Fall back to gcc_s if available.
+macro(add_libgcc_library)
+  # split space-separated vars into a list
+  set(libgcc_cmd ${CMAKE_C_COMPILER}
+                 ${CMAKE_SHARED_LIBRARY_CXX_FLAGS}
+                 ${CMAKE_CXX_FLAGS}
+                 ${CMAKE_SHARED_LINKER_FLAGS}
+                 -print-libgcc-file-name)
+
+  execute_process(
+    COMMAND "${libgcc_cmd}"
+    RESULT_VARIABLE libgcc_check_ret
+    OUTPUT_VARIABLE libgcc_path
+    OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+    if (${libgcc_check_ret} EQUAL 0)
+      add_library_flags("${libgcc_path}")
+    else()
+      add_library_flags_if(LIBCXX_HAS_GCC_S_LIB gcc_s)
+    endif()
+endmacro()
+
 # Turn a comma separated CMake list into a space separated string.
 macro(split_list listname)
   string(REPLACE ";" " " ${listname} "${${listname}}")


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