[PATCH] D39244: [sanitizer] Random shuffling of chunks for the 32-bit Primary Allocator

[Kostya Kortchinsky via Phabricator via llvm-commits]

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

The 64-bit primary has had random shuffling of chunks for a while, this
implements it for the 32-bit primary. Scudo is currently the only user of
`kRandomShuffleChunks`.

This change consists of a few modifications:

- move the random shuffling functions out of the 64-bit primary to `sanitizer_common.h`. Alternatively I could move them to `sanitizer_allocator.h` as they are only used in the allocator, I don't feel strongly either way;
- small change in the 64-bit primary to make the `rand_state` initialization `UNLIKELY`;
- addition of a `rand_state` in the 32-bit primary's `SizeClassInfo` and shuffling of chunks when populating the free list.
- enabling the `random_shuffle.cpp` test on platforms using the 32-bit primary for Scudo.

Some comments on why the shuffling is done that way. Initially I just
implemented a `Shuffle` function in the `TransferBatch` which was simpler but I
came to realize this wasn't good enough: for chunks of 10000 bytes for example,
with a `CompactSizeClassMap`, a batch holds only 1 chunk, meaning shuffling the
batch has no effect, while a region is usually 1MB, eg: 104 chunks of that size.
So I decided to "stage" the newly gathered chunks in a temporary array that
would be shuffled prior to placing the chunks in batches.
The result is looping twice through n_chunks even if shuffling is not enabled,
but I didn't notice any significant significant performance impact.


https://reviews.llvm.org/D39244

Files:
  lib/sanitizer_common/sanitizer_allocator_primary32.h
  lib/sanitizer_common/sanitizer_allocator_primary64.h
  lib/sanitizer_common/sanitizer_common.h
  test/scudo/random_shuffle.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D39244.120078.patch
Type: text/x-patch
Size: 5924 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20171024/42b554db/attachment.bin>