[clang] [compiler-rt] [sanitizer] Add DoubleFreeSanitizer (DSan) (PR #213846)

[Bojun Seo via llvm-commits]

Bojun-Seo wrote:

> I think the consensus in [this thread](https://discourse.llvm.org/t/rfc-introduction-of-doublefreesanitizer-dsan/91363/16) was having a dedicated tool that is a subset or very closely overlapping of a range of other tools (ASan, Scudo, GWP-ASan, LSan, etc.) in compiler-rt doesn't make much sense. You've evaluated against the no-instrument-ASan option, but did you manage to prototype the **out-of-tree option**? Why does it need to be part of compiler-rt? Because you do not need compiler instrumentation, the flag `-fsanitize=doublefree` is a convenience and not technically needed, and a pure runtime tool can be standalone out-of-tree.

Following @vitalybuka 's request, I am no longer planning to add this as a dedicated tool in compiler-rt. Instead, I am implementing double-free detection as an extension to LSan.

Your points are very reasonable. While there are trade-offs, I also agree that keeping this functionality out-of-tree is a viable and good option.

I would like to gather more community feedback on the RFC. Between the two approaches — extending LSan or maintaining it out-of-tree — which one do people prefer? I will follow the consensus.

https://github.com/llvm/llvm-project/pull/213846