[LLVMdev] Unifying TSan blacklist and no_sanitize_thread

[Dmitry Vyukov]

On Fri, May 30, 2014 at 12:41 AM, Alexey Samsonov <vonosmas at gmail.com> wrote:
> Hi,
>
> I consider reducing the usage of blacklist in sanitizer instrumentation
> passes and doing the necessary work in frontend (Clang) instead.
>
> Some of it is already implemented: e.g. Clang will attach an attribute
> "sanitize_address" to function definition only if this function is not
> blacklisted. In this case we won't instrument the memory accesses in this
> function in ASan instrumentation pass, so there's no need to looking at
> blacklist once again.
>
> TSan pass does the following:
>
> 1) instruments plain memory accesses
> 2) instruments atomic accesses
> 3) instruments memory intrinsics calls.
> 4) adds function entry/exit callbacks.
>
> If a function doesn't have sanitize_thread attribute (e.g. it was annotated
> with __attribute__((no_sanitize_thread)) ), then it still does (2), (3) and
> (4). If a function is blacklisted,
> TSan pass does nothing. Shouldn't the behavior be the same? I think, we must
> always do (4) to get
> good stack traces, and probably do (2) (we may report races on atomics in
> this case, but otherwise
> we may miss synchronization). Thoughts?


We don't know how this functionality must work because we don't use it.
It's possible to invent use cases for all 16 permutations of 1/2/3/4.
I think we need to stick with omitting instrumentation of memory
accesses (and intrinsics, at least with best effort), but keep
instrumentation of atomics and func enter/exit. This covers probably
the most common use cases of suppressing known races and improving
performance. Atomics are generally needed to prevent false positives,
so it's risky to remove them. Func enter/exit are needed for good
reports.