Make CompilerType safe

When a process gets restarted TypeSystem objects associated with it
may get deleted, and any CompilerType objects holding on to a
reference to that type system are a use-after-free in waiting. Because
of the SBAPI, we don't have tight control over where CompilerTypes go
and when they are used. This is particularly a problem in the Swift
plugin, where the scratch TypeSystem can be restarted while the
process is still running. The Swift plugin has a lock to prevent
abuse, but where there's a lock there can be bugs.

This patch changes CompilerType to store a std::weak_ptr<TypeSystem>.
Most of the std::weak_ptr<TypeSystem>* uglyness is hidden by
introducing a wrapper class CompilerType::WrappedTypeSystem that has a
dyn_cast_or_null() method. The only sites that need to know about the
weak pointer implementation detail are the ones that deal with
creating TypeSystems.

rdar://101505232

Differential Revision: https://reviews.llvm.org/D136650

1 files changed, 5 insertions, 4 deletions

diff --git a/lldb/source/Core/DumpDataExtractor.cpp b/lldb/source/Core/DumpDataExtractor.cpp
index 0bf6722340fe..ec98d6266241 100644
--- a/lldb/source/Core/DumpDataExtractor.cpp
+++ b/lldb/source/Core/DumpDataExtractor.cpp
@@ -320,11 +320,12 @@ printMemoryTags(const DataExtractor &DE, Stream *s, lldb::addr_t addr,
 static const llvm::fltSemantics &GetFloatSemantics(const TargetSP &target_sp,
                                                    size_t byte_size) {
   if (target_sp) {
-    if (auto type_system_or_err =
-            target_sp->GetScratchTypeSystemForLanguage(eLanguageTypeC))
-      return type_system_or_err->GetFloatTypeSemantics(byte_size);
-    else
+    auto type_system_or_err =
+      target_sp->GetScratchTypeSystemForLanguage(eLanguageTypeC);
+    if (!type_system_or_err)
       llvm::consumeError(type_system_or_err.takeError());
+    else if (auto ts = *type_system_or_err)
+      return ts->GetFloatTypeSemantics(byte_size);
   }
   // No target, just make a reasonable guess
   switch(byte_size) {