[Lldb-commits] [PATCH] D20671: [cmake] Add a big warning about a libstdc++ issue

[Pavel Labath via lldb-commits]

labath created this revision.
labath added reviewers: tberghammer, tfiala, nitesh.jain, omjavaid, emaste, krytarowski.
labath added a subscriber: lldb-commits.

Recent increase in the usage of std::weak_ptr has caused us to rediscover an issue in libstdc++
versions prior to 4.9 <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59656>, which make this class
unusable without exceptions in the presence of multiple threads. It's virtualy impossible to work
around this issue without implementing our own shared_ptr/weak_ptr substitutes, which does not
seem like a good idea.

Therefore, I am adding a big CMake warning which warns you about this issue if you're attempting
a to do a build which is suceptible to this problem and suggests possible alternatives. Right
now, nothing spectacular will happen if you ignore this warning (all the crashes I have seen
occur during process shutdown), but there's no guarantee the situation will not change in the
future.

http://reviews.llvm.org/D20671

Files:
  cmake/modules/LLDBConfig.cmake

Index: cmake/modules/LLDBConfig.cmake
===================================================================
--- cmake/modules/LLDBConfig.cmake
+++ cmake/modules/LLDBConfig.cmake
@@ -1,3 +1,5 @@
+include(CheckCXXSymbolExists)
+
 set(LLDB_PROJECT_ROOT ${CMAKE_CURRENT_SOURCE_DIR})
 set(LLDB_SOURCE_ROOT "${CMAKE_CURRENT_SOURCE_DIR}/source")
 set(LLDB_INCLUDE_ROOT "${CMAKE_CURRENT_SOURCE_DIR}/include")
@@ -415,3 +417,25 @@
     list(APPEND system_libs ${CURSES_LIBRARIES})
     include_directories(${CURSES_INCLUDE_DIR})
 endif ()
+
+check_cxx_symbol_exists("__GLIBCXX__" "string" LLDB_USING_LIBSTDCXX)
+if(LLDB_USING_LIBSTDCXX)
+    # There doesn't seem to be an easy way to check the library version. Instead, we rely on the
+    # fact that std::set did not have the allocator constructor available until version 4.9
+    check_cxx_source_compiles("
+            #include <set>
+            std::set<int> s = std::set<int>(std::allocator<int>());
+            int main() { return 0; }"
+            LLDB_USING_LIBSTDCXX_4_9)
+    if (NOT LLDB_USING_LIBSTDCXX_4_9 AND NOT LLVM_ENABLE_EH)
+        message(WARNING
+            "You appear to be using linking to libstdc++ version lesser than 4.9 without "
+            "exceptions enabled. These versions of the library have an issue, which causes "
+            "occasional lldb crashes. See <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59656> "
+            "for details. Possible courses of action are:\n"
+            "- use libstdc++ version 4.9 or newer\n"
+            "- use libc++ (via LLVM_ENABLE_LIBCXX)\n"
+            "- enable exceptions (via LLVM_ENABLE_EH)\n"
+            "- ignore this warning and accept occasional instability")
+    endif()
+endif()


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