[PATCH] D40657: [sanitizer] Introduce a vDSO aware time function, and use it in the allocator

[Kostya Kortchinsky via Phabricator via llvm-commits]

cryptoad created this revision.
Herald added subscribers: kubamracek, srhines.

`NanoTime` is a time sink when checking whether or not to release memory to
the OS. While reducing the amount of calls to said function is in the works,
another solution that was found to be beneficial was to use a timing function
that can leverage the vDSO.

We hit a couple of snags along the way, like the fact that the glibc crashes
when `clock_gettime` is called from a `preinit_array`, or the fact that
`__vdso_clock_gettime` is mangled (for security purposes) and can't be used
directly, and also that `clock_gettime` can be intercepted.

The proposed solution takes care of all this as far as I can tell, and
significantly improve performances and some Scudo load tests with memory
reclaiming enabled.

@krytarowski: could you please chime in on the NetBSD aspect of it?


https://reviews.llvm.org/D40657

Files:
  lib/sanitizer_common/sanitizer_allocator_primary64.h
  lib/sanitizer_common/sanitizer_common.h
  lib/sanitizer_common/sanitizer_common_interceptors.inc
  lib/sanitizer_common/sanitizer_fuchsia.cc
  lib/sanitizer_common/sanitizer_linux.cc
  lib/sanitizer_common/sanitizer_win.cc
  lib/scudo/scudo_tsd.h

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