[GWP-ASan] [heapprofd] Use ephemeral dispatch table when death prof.

GWP-ASan + heapprofd don't currently play nice together in some
circumstances. heapprofd thinks it's still an only child, and refuses to
accept the existence of its little brother, GWP-ASan.

If GWP-ASan is installed before heapprofd, then heapprofd is *required*
to respect that libc has a favourite child. If an allocation/free is passed
to heapprofd, then heapprofd *must* (eventually) pass that allocation/free to
GWP-ASan. If heapprofd doesn't do this, then a free() of a GWP-ASan
allocation can be passed to the system allocator.

This can happen in two places right now:
 1. The heapprofd hooks simply clobber any trace of what was
 previously in the default_dispatch_table when enabled through the
 heapprofd signal.
 2. Heapprofd can die when the system is under significant pressure.
 Some pipes can timeout, which ends up in the client calling ShutdownLazy()
 -> mallopt(M_RESET_HOOKS) -> DispatchReset(). This also clobbers any
 trace of the previous default_dispatch_table.

To fix both these problems, we fix heapprofd to restore the previous
default_dispatch_table whenever either circumstance happens. We do some
tricky copying to avoid race conditions on the malloc_dispatch_table in
fixing #1.

Bug: 135634846
Test: Run HeapprofdEndToEnd.NativeProfilingActiveAtProcessExit/ForkMode
a significant number of times with large amounts of system pressure (I
just run bionic-unit-tests-scudo in parallel). You will see some test
failures where heapprofd died due to system pressure, but never a death
from the allocator. Tests should never fail when the system isn't under
immense pressure.

Change-Id: I20ab340d4bdc35d6d1012da5ee1a25634428d097

0 files changed, 0 insertions, 0 deletions