[compiler-rt] [win/asan] Don't intercept memset etc. in ntdll (PR #120397)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

This patch seems to have broken asan, when running on top of msvcrt.dll (rather than UCRT); this came up when trying to build a release of 20.1.0 RC 1 with msvcrt.dll, at https://github.com/mstorsjo/llvm-mingw/actions/runs/13123676548/job/36623780321. Whenever a process is started, it errors out with this message:
```
AddressSanitizer: CHECK failed: sanitizer_common_interceptors_memintrinsics.inc:239 "((__interception::real_memcpy)) != (0)" (0x0, 0x0) (tid=1128)
```

Given the list of potential DLLs that are attempted to intercept at https://github.com/llvm/llvm-project/blob/69ebac7ad6ae1db9bb19cf3a19ea978af6034ca3/compiler-rt/lib/interception/interception_win.cpp#L1175-L1195, I see that we don't include `msvcrt.dll` in there. I guess that means that previously, the only case of e.g. `memcpy` that was intercepted, was from `ntdll.dll`. For e.g. UCRT builds, we'd also find one in `ucrtbase.dll`, but here we no longer find any at all.

Intercepting `msvcrt.dll` is a bit special though, because even if the user code uses UCRT, most processes end up loading `msvcrt.dll` as well, because this is used by most system DLLs. And I guess in this case, it may have already been used before we get to intercepting it?

I did try adding `msvcrt.dll` to this list, but that doesn't seem to fix the issue entirely either - I'm ending up with errors like this instead:
```
==5236==ERROR: AddressSanitizer: attempting to call malloc_usable_size() for pointer which is not owned:
```

For further context; asan wasn't entirely working in `msvcrt.dll` builds anyway, as far as I  know (I've had a couple of reports where it doesn't, while it works fine in UCRT builds). But it seems to have been working well enough to pass my very minimal smoke tests at least.

I'm wondering what others think about this, which way we should go:
- Reinstate intercepting `ntdll.dll`, if building for mingw + `msvcrt.dll`. While it isn't the entirely right thing to do, we should reach the same level of functionality as before
- Try to intercept `msvcrt.dll`, possibly only in the mingw + `msvcrt.dll` case. But that apparently seems like it would require more work than just adding it to the list.
- Just give up on asan on `msvcrt.dll` - skip testing those aspects in such builds (and maybe skip shipping those DLLs entirely in such builds?)

What do e.g. @alvinhochun @bernhardu @cjacek @lazka @mati865 think about that?



https://github.com/llvm/llvm-project/pull/120397