AsanThread::Destroy implementation expected to be called on
child thread.
I missed authors concern regarding this reviewing D95184.
Reviewed By: delcypher
Differential Revision: https://reviews.llvm.org/D95731
Previously in ASan's `pthread_create` interceptor we would block in the
`pthread_create` interceptor waiting for the child thread to start.
Unfortunately this has bad performance characteristics because the OS
scheduler doesn't know the relationship between the parent and child
thread (i.e. the parent thread cannot make progress until the child
thread makes progress) and may make the wrong scheduling decision which
stalls progress.
It turns out that ASan didn't use to block in this interceptor but was
changed to do so to try to address
http://llvm.org/bugs/show_bug.cgi?id=21621/.
In that bug the problem being addressed was a LeakSanitizer false
positive. That bug concerns a heap object being passed
as `arg` to `pthread_create`. If:
* The calling thread loses a live reference to the object (e.g.
`pthread_create` finishes and the thread no longer has a live
reference to the object).
* Leak checking is triggered.
* The child thread has not yet started (once it starts it will have a
live reference).
then the heap object will incorrectly appear to be leaked.
This bug is covered by the `lsan/TestCases/leak_check_before_thread_started.cpp` test case.
In b029c5101fb49b3577a1c322f42ef9fc616f25bf ASan was changed to block
in `pthread_create()` until the child thread starts so that `arg` is
kept alive for the purposes of leaking check.
While this change "works" its problematic due to the performance
problems it causes. The change is also completely unnecessary if leak
checking is disabled (via detect_leaks runtime option or
CAN_SANITIZE_LEAKS compile time config).
This patch does two things:
1. Takes a different approach to solving the leak false positive by
making LSan's leak checking mechanism treat the `arg` pointer of
created but not started threads as reachable. This is done by
implementing the `ForEachRegisteredThreadContextCb` callback for
ASan.
2. Removes the blocking behaviour in the ASan `pthread_create`
interceptor.
rdar://problem/63537240
Differential Revision: https://reviews.llvm.org/D95184
While some platforms call `AsanThread::Init()` from the context of the
thread being started, others (like Fuchsia) call `AsanThread::Init()`
from the context of the thread spawning a child. Since
`AsyncSignalSafeLazyInitFakeStack` writes to a thread-local, we need to
avoid calling it from the spawning thread on Fuchsia. Skipping the call
here on Fuchsia is fine; it'll get called from the new thread lazily on first
attempted access.
Reviewed By: vitalybuka
Differential Revision: https://reviews.llvm.org/D89607
When enabling stack use-after-free detection, we discovered that we read
the thread ID on the main thread while it is still set to 2^24-1.
This patch moves our call to AsanThread::Init() out of CreateAsanThread,
so that we can call SetCurrentThread first on the main thread.
Reviewed By: mcgrathr
Differential Revision: https://reviews.llvm.org/D89606
Do not crash when AsanThread::GetStackVariableShadowStart does not find
a variable for a pointer on a shadow stack.
Differential Revision: https://reviews.llvm.org/D89552
