[CMake] Link to compiler-rt if LIBUNWIND_USE_COMPILER_RT is ON.

[cdavis5x]

Summary

If -nodefaultlibs is given, we weren't actually linking to it. This
was true irrespective of passing -rtlib=compiler-rt (see previous
patch). Now we explicitly link it to handle that case.

I wonder if we should be linking these libraries only if we're using
-nodefaultlibs...

[cdavis5x]

Ping.

[cdavis5x]

Ping.

[rnk]

Looks good, sorry for the delay.

[mstorsjo]

src/CMakeLists.txt

60 ↗

(On Diff #163910)

I'm a little suspicious of this line, of forcibly linking against libgcc here, even if we might not have checked that it even exists.

[cdavis5x]

• Detect libgcc.

libunwind/trunk/cmake/config-ix.cmake

 
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 include(CheckLibraryExists)
 
 check_library_exists(c fopen "" LIBUNWIND_HAS_C_LIB)
 
 if (NOT LIBUNWIND_USE_COMPILER_RT)
   check_library_exists(gcc_s __gcc_personality_v0 "" LIBUNWIND_HAS_GCC_S_LIB)
+  check_library_exists(gcc __absvdi2 "" LIBUNWIND_HAS_GCC_LIB)
 endif()
 
 # libunwind is built with -nodefaultlibs, so we want all our checks to also
 # use this option, otherwise we may end up with an inconsistency between
 # the flags we think we require during configuration (if the checks are
 # performed without -nodefaultlibs) and the flags that are actually
 # required during compilation (which has the -nodefaultlibs). libc is
 # required for the link to go through. We remove sanitizers from the
 # configuration checks to avoid spurious link errors.
 check_c_compiler_flag(-nodefaultlibs LIBUNWIND_HAS_NODEFAULTLIBS_FLAG)
 if (LIBUNWIND_HAS_NODEFAULTLIBS_FLAG)
   set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nodefaultlibs")
   if (LIBUNWIND_HAS_C_LIB)
     list(APPEND CMAKE_REQUIRED_LIBRARIES c)
   endif ()
   if (LIBUNWIND_USE_COMPILER_RT)
     find_compiler_rt_library(builtins LIBUNWIND_BUILTINS_LIBRARY)
     list(APPEND CMAKE_REQUIRED_LIBRARIES "${LIBUNWIND_BUILTINS_LIBRARY}")
-  elseif (LIBUNWIND_HAS_GCC_S_LIB)
+  else ()
+    if (LIBUNWIND_HAS_GCC_S_LIB)
       list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)
     endif ()
+    if (LIBUNWIND_HAS_GCC_LIB)
+      list(APPEND CMAKE_REQUIRED_LIBRARIES gcc)
+    endif ()
+  endif ()
   if (MINGW)
     # Mingw64 requires quite a few "C" runtime libraries in order for basic
     # programs to link successfully with -nodefaultlibs.
     if (LIBUNWIND_USE_COMPILER_RT)
       set(MINGW_RUNTIME ${LIBUNWIND_BUILTINS_LIBRARY})
     else ()
       set(MINGW_RUNTIME gcc_s gcc)
     endif()

libunwind/trunk/src/CMakeLists.txt

 set(LIBUNWIND_SOURCES
     ${LIBUNWIND_CXX_SOURCES}
     ${LIBUNWIND_C_SOURCES}
     ${LIBUNWIND_ASM_SOURCES})
 
 # Generate library list.
 set(libraries)
 append_if(libraries LIBUNWIND_HAS_C_LIB c)
+if (LIBUNWIND_USE_COMPILER_RT)
+  list(APPEND libraries "${LIBUNWIND_BUILTINS_LIBRARY}")
+else()
   append_if(libraries LIBUNWIND_HAS_GCC_S_LIB gcc_s)
+  append_if(libraries LIBUNWIND_HAS_GCC_LIB gcc)
+endif()
 append_if(libraries LIBUNWIND_HAS_DL_LIB dl)
 if (LIBUNWIND_ENABLE_THREADS)
   append_if(libraries LIBUNWIND_HAS_PTHREAD_LIB pthread)
 endif()
 
 # Setup flags.
 append_if(LIBUNWIND_CXX_FLAGS LIBUNWIND_HAS_NO_RTTI_FLAG -fno-rtti)