[Lldb-commits] [PATCH] D137983: [lldb] Disable looking at pointee types to find synthetic value for non-ObjC

[Arthur Eubanks via Phabricator via lldb-commits]

aeubanks added a comment.

In D137983#3930973 <https://reviews.llvm.org/D137983#3930973>, @labath wrote:

> We have tests for shared libraries (grep for DYLIB_C(XX)_SOURCES)), but it's easier to reproduce this problem by compiling one CU with -g0 -- see inline comment. (If you are creating an "API" test for this, beware that their default is to build everything with -fstandalone-debug, and you'll need to explicitly change that (see LIMIT_DEBUG_INFO_FLAGS))

`lldb/test/API/lang/cpp/incomplete-types/` looks like exactly what I want, I've added a test based on that (and verified that lldb crashes in that test without the source change)

> This behavior (bug) is triggered by the `FrontEndWantsDereference` formatter flag, which is why it manifests itself for (libc++) vector and friends. The ObjC formatters don't set that flag so they should be safe. The libstdc++ formatters don't set it either. Furthermore there doesn't seem to be a way to set this flag by the user, so it is not possible to create a libc++-independent reproducer (which is what I was going to suggest).
>
> I've been looking for a better way to fix this today (sorry about the delay), but I haven't figured out anything better. There is this fundamental recursion between the pretty printer (which wants to dereference a value) and the dereferencing code (which wants to know if it has a pretty printer -- so it can avoid dereferencing). Just removing the `HasSyntheticValue()`fixed the bug for me -- but then we were able to "dereference" incomplete structs. It's possible we may be able to allow the dereference to succeed here, but then refuse to print the value somewhere down the line. I would like to hear what @jingham things about all this.

Thanks for the investigation!
Actually some libstdc++ formatters do also set `FrontEndWantsDereference`, so this is reproable with

  $ cat /tmp/main.cc
  #include <set>
  
  void f(std::set<int>& v);
  
  int main() {
          std::set<int> v;
          f(v);
  }
  $ cat /tmp/a.cc
  #include <set>
  
  void f(std::set<int>& v) {
          // break
  }
  $ bin/clang++ -g0 /tmp/main.cc -o /tmp/main.o  -c && bin/clang++ -g /tmp/a.cc -o /tmp/a.o  -c && bin/clang++ /tmp/a.o /tmp/main.o -o /tmp/a
  $ bin/lldb /tmp/a -b -o 'br set -n f'  -o run

with and without `-stdlib=libc++`

maybe a more targeted solution would be to change the added condition to when `FrontEndWantsDereference` is set, but that's more annoying to thread through the code. I think this should be ok as a temporary workaround if we don't have a proper fix soonish?


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https://reviews.llvm.org/D137983