Use libunwind as an imported target

When UNWIND_LIBRARY is used directly as a public dependency then
absolute path is stored in cmake config file. This is an issue when
glog is used as part of an SDK, which was built somewhere else. When
SDK is installed on developer's machine, cmake config contains a full
path to non-existent location. The solution is to find libunwind
during configure stage and store target name as a dependency, not a full path.
Cmake module looks for libunwind and libunwind-PLAT, where PLAT is one of
supported platforms.
Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>

CMakeLists.txt

@@ -65,7 +65,6 @@ check_include_file (dlfcn.h HAVE_DLFCN_H)
 check_include_file (execinfo.h HAVE_EXECINFO_H)
 check_include_file (glob.h HAVE_GLOB_H)
 check_include_file (inttypes.h HAVE_INTTYPES_H)
-check_include_file (libunwind.h HAVE_LIBUNWIND_H)
 check_include_file (memory.h HAVE_MEMORY_H)
 check_include_file (pwd.h HAVE_PWD_H)
 check_include_file (stdint.h HAVE_STDINT_H)
@@ -81,7 +80,6 @@ check_include_file (syscall.h HAVE_SYSCALL_H)
 check_include_file (syslog.h HAVE_SYSLOG_H)
 check_include_file (ucontext.h HAVE_UCONTEXT_H)
 check_include_file (unistd.h HAVE_UNISTD_H)
-check_include_file (unwind.h HAVE_UNWIND_H)
 check_include_file (pwd.h HAVE_PWD_H)
 
 check_include_file_cxx ("ext/hash_map" HAVE_EXT_HASH_MAP)
@@ -117,11 +115,9 @@ check_cxx_compiler_flag (-Wunnamed-type-template-args
 # snprintf as an inline function
 check_symbol_exists (snprintf stdio.h HAVE_SNPRINTF)
 
-check_library_exists (unwind get_static_proc_name "" HAVE_LIB_UNWIND)
 check_library_exists (dbghelp UnDecorateSymbolName "" HAVE_DBGHELP)
 
-find_library (UNWIND_LIBRARY NAMES unwind DOC "unwind library")
-mark_as_advanced (UNWIND_LIBRARY)
+find_package(Libunwind)
 
 check_c_source_compiles ("
 #include <stdlib.h>
@@ -491,9 +487,9 @@ add_library(glog::glog ALIAS glog)
 
 set_target_properties (glog PROPERTIES POSITION_INDEPENDENT_CODE ON)
 
-if (UNWIND_LIBRARY)
-  target_link_libraries (glog PUBLIC ${UNWIND_LIBRARY})
-endif (UNWIND_LIBRARY)
+if (Libunwind_FOUND)
+  target_link_libraries (glog PUBLIC unwind)
+endif (Libunwind_FOUND)
 
 if (HAVE_DBGHELP)
    target_link_libraries (glog PUBLIC dbghelp)
@@ -705,6 +701,7 @@ export (PACKAGE glog)
 install (FILES
   ${CMAKE_CURRENT_BINARY_DIR}/glog-config.cmake
   ${CMAKE_CURRENT_BINARY_DIR}/glog-config-version.cmake
+  ${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindLibunwind.cmake
   DESTINATION ${_glog_CMake_INSTALLDIR})
 
 install (EXPORT glog-targets NAMESPACE glog:: DESTINATION

cmake/FindLibunwind.cmake

+# - Try to find libunwind
+# Once done this will define
+#
+#  Libunwind_FOUND - system has libunwind
+#  unwind - cmake target for libunwind
+
+find_library (UNWIND_LIBRARY NAMES unwind DOC "unwind library")
+include (CheckIncludeFile)
+check_include_file (libunwind.h HAVE_LIBUNWIND_H)
+check_include_file (unwind.h HAVE_UNWIND_H)
+
+if (CMAKE_SYSTEM_PROCESSOR MATCHES "^arm")
+    set(LIBUNWIND_ARCH "arm")
+elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^aarch64")
+    set(LIBUNWIND_ARCH "aarch64")
+elseif (CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64" OR
+        CMAKE_SYSTEM_PROCESSOR STREQUAL "amd64" OR
+        CMAKE_SYSTEM_PROCESSOR STREQUAL "corei7-64")
+    set(LIBUNWIND_ARCH "x86_64")
+elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^i.86$")
+    set(LIBUNWIND_ARCH "x86")
+elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^ppc64")
+    set(LIBUNWIND_ARCH "ppc64")
+elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^ppc")
+    set(LIBUNWIND_ARCH "ppc32")
+elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^mips")
+    set(LIBUNWIND_ARCH "mips")
+elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^hppa")
+    set(LIBUNWIND_ARCH "hppa")
+elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^ia64")
+    set(LIBUNWIND_ARCH "ia64")
+endif()
+
+find_library (UNWIND_LIBRARY_PLATFORM NAMES "unwind-${LIBUNWIND_ARCH}" DOC "unwind library platform")
+if (UNWIND_LIBRARY_PLATFORM)
+    set(HAVE_LIB_UNWIND "1")
+endif()
+
+include(FindPackageHandleStandardArgs)
+# handle the QUIETLY and REQUIRED arguments and set Libunwind_FOUND to TRUE
+# if all listed variables are TRUE
+find_package_handle_standard_args(Libunwind DEFAULT_MSG
+    UNWIND_LIBRARY HAVE_LIBUNWIND_H HAVE_UNWIND_H HAVE_LIB_UNWIND)
+
+mark_as_advanced (UNWIND_LIBRARY UNWIND_LIBRARY_PLATFORM)
+
+if (Libunwind_FOUND)
+    add_library(unwind INTERFACE IMPORTED)
+    set_target_properties(unwind PROPERTIES
+        INTERFACE_LINK_LIBRARIES "${UNWIND_LIBRARY};${UNWIND_LIBRARY_PLATFORM}"
+    )
+else()
+    message("Can't find libunwind library")
+endif()
+

glog-config.cmake.in

@@ -8,4 +8,7 @@ include (CMakeFindDependencyMacro)
 
 @gflags_DEPENDENCY@
 
+list (APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
+find_dependency (Libunwind)
+
 include ("${CMAKE_CURRENT_LIST_DIR}/glog-targets.cmake")