[scudo][standalone] Fork support

Summary:
fork() wasn't well (or at all) supported in Scudo. This materialized
in deadlocks in children.

In order to properly support fork, we will lock the allocator pre-fork
and unlock it post-fork in parent and child. This is done via a
`pthread_atfork` call installing the necessary handlers.

A couple of things suck here: this function allocates - so this has to
be done post initialization as our init path is not reentrance, and it
doesn't allow for an extra pointer - so we can't pass the allocator we
are currently working with.

In order to work around this, I added a post-init template parameter
that gets executed once the allocator is initialized for the current
thread. Its job for the C wrappers is to install the atfork handlers.

I reorganized a bit the impacted area and added some tests, courtesy
of cferris@ that were deadlocking prior to this fix.

Subscribers: jfb, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D72470

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler-rt/lib/scudo/standalone/wrappers_cpp.cpp b/compiler-rt/lib/scudo/standalone/wrappers_cpp.cpp
index 72235e9c982..1da5385c778 100644
--- a/compiler-rt/lib/scudo/standalone/wrappers_cpp.cpp
+++ b/compiler-rt/lib/scudo/standalone/wrappers_cpp.cpp
@@ -15,7 +15,8 @@
 
 #include <stdint.h>
 
-extern scudo::Allocator<scudo::Config> *AllocatorPtr;
+extern "C" void malloc_postinit();
+extern scudo::Allocator<scudo::Config, malloc_postinit> *AllocatorPtr;
 
 namespace std {
 struct nothrow_t {};