[Lldb-commits] [PATCH] D136650: Add a check for TypeSystem use-after-free problems

[Will Hawkins via Phabricator via lldb-commits]

hawkinsw added a comment.

There are *so* many reasons that I love this patch.

First and foremost: I am a professor of computer science at University of Cincinnati and teaching Programming Languages this semester and I am about to teach *this very technique* for protecting against use-after-free errors. Having seen this patch I now have a great example of where it is used in real life! So, thank you!

Second, I have left some comments but please take what I said with a grain of salt. I hope that it is helpful and not a waste of time.

Thank you!
Will



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Comment at: lldb/source/Symbol/CompilerType.cpp:35
+  bool unused;
+  if (GetTypeSystemGraveyard().Lookup(m_type_system, unused)) {
+    lldbassert(false && "CompilerType belongs to deleted Typesystem");
----------------
I am sorry if this is obvious, but is `CompilerType` used in a multithreaded environment? So, is there a possibility that we could pass the check on line 32 but become invalid by the use of `m_type_system` here and fall victim to an attempt (in `Lookup`, perhaps?) to dereference a `NULL` pointer? Again, I am sorry if that is a stupid question!


================
Comment at: lldb/source/Symbol/CompilerType.cpp:36
+  if (GetTypeSystemGraveyard().Lookup(m_type_system, unused)) {
+    lldbassert(false && "CompilerType belongs to deleted Typesystem");
+    return false;
----------------
I know that this is a nit, but should we write `TypeSystem`?


================
Comment at: lldb/source/Symbol/TypeSystem.cpp:22
+  // Intentionally leaked to avoid C++ destructor ordering issue.
+  static TypeSystemSet *g_typesystem_graveyard = new TypeSystemSet();
+  return *g_typesystem_graveyard;
----------------
I spent *way* too long researching to make sure that this initialization is thread safe and wanted to drop a link here in case anyone is wondering the same thing:

[C++ standard: stmt.dcl para 3, sentence 3](http://eel.is/c++draft/stmt.dcl#3.sentence-3)


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D136650/new/

https://reviews.llvm.org/D136650