[PATCH] D61867: [GWP-ASan] Initial build files, implementation of PRNG [1].

[Matt Morehouse via Phabricator via llvm-commits]

morehouse accepted this revision.
morehouse added inline comments.
This revision is now accepted and ready to land.


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Comment at: compiler-rt/lib/gwp_asan/random.cpp:28
+                                                 xorShift32(), xorShift32(),
+                                                 xorShift32(), xorShift32()};
+  uint32_t Temp = RandomState[0] ^ (RandomState[0] >> 2);
----------------
hctim wrote:
> morehouse wrote:
> > This seems like a lot of state to keep.  Not a big deal, but is there a simpler RNG we can use?  What about just xorshift32?
> `xorwow` has a period of `2 ** 192 - 2**32`, versus `xorshift32` having a period of `2 ** 32`. Also, surprisingly, it's about 1.2x faster than `xorshift32` (http://quick-bench.com/mYmSCp5jJ_NLo3yyPXt-2N3TuHg) on my x86_64.
> 
> I personally think the 20B extra TLS/thread is worth it (given that it's likely zero overhead anyway unless the 20B pushes someone to alloc a new page for TLS). WDYT?
2^32 seems plenty large to me.  Speed isn't a huge concern since we're on the slow path, so I personally would prefer simpler.  In fact if the RNG func is small enough, it might be simpler to put it directly in GPA.cc instead and reduce the number of files.


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https://reviews.llvm.org/D61867