arena: derive alignment unit from std::max_align_t

Summary:
As raised in #2265, the arena allocator will return memory that is improperly aligned to store a `std::function` on macOS. Oddly, I'm unable to tickle this bug without adding a `std::function` field to `struct ReadOptions`—but my proposal in #2265 does exactly that.

In any case, here's a simple reproduction. Apply this bogus patch to get a `std::function` into `struct ReadOptions`

```
 --- a/include/rocksdb/options.h
+++ b/include/rocksdb/options.h
@@ -1035,6 +1035,8 @@ struct ReadOptions {
   // Default: 0
   uint64_t max_skippable_internal_keys;

+  std::function<void()> foo;
+
   ReadOptions();
   ReadOptions(bool cksum, bool cache);
 };
```

then compile `db_properties_test` *with ubsan* and run `ReadLatencyHistogramByLevel`:

```
$ make COMPILE_WITH_UBSAN=1 db_properties_test
$ ./db_properties_test --gtest_filter=DBPropertiesTest.ReadLatencyHistogramByLevel
```

ubsan will complain about several misaligned accesses:

```
Note: Google Test filter = DBPropertiesTest.ReadLatencyHistogramByLevel
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from DBPropertiesTest
[ RUN      ] DBPropertiesTest.ReadLatencyHistogramByLevel
util/coding.h:372:12: runtime error: load of misaligned address 0x00010d85516c for type 'const unsigned long', which requires 8 byte alignment
0x00010d85516c: note: pointer points here
  01 00 34 57 00 00 00 00  02 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  78 24 82 0a 01 00 00 00
              ^
util/coding.h:362:3: runtime error: store to misaligned address 0x7fff5733fac4 for type 'unsigned long', which requires 8 byte alignment
0x7fff5733fac4: note: pointer points here
  01 00 00 00 00 00 00 00  02 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  80 1d 96 0d 01 00 00 00
              ^
util/coding.h:372:12: runtime error: load of misaligned address 0x00010d85516c for type 'const unsigned long', which requires 8 byte alignment
0x00010d85516c: note: pointer points here
  01 00 34 57 00 00 00 00  02 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  78 24 82 0a 01 00 00 00
              ^
version_set.cc:854: runtime error: constructor call on misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
version_set.cc:512: runtime error: constructor call on misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
version_set.cc:505: runtime error: constructor call on misaligned address 0x00010dbfa5e8 for type 'rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
options.h:931: runtime error: constructor call on misaligned address 0x00010dbfa5e8 for type 'rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
options.h:931: runtime error: constructor call on misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
functional:1583: runtime error: constructor call on misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1585:9: runtime error: member access within misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1585:9: runtime error: store to misaligned address 0x00010dbfa648 for type '__base *' (aka '__base<void ()> *'), which requires 16 byte alignment
0x00010dbfa648: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
db/version_set.cc:864:29: runtime error: upcast of misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:521:12: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:521:12: runtime error: load of misaligned address 0x00010dbfa5d8 for type 'rocksdb::TableCache *', which requires 16 byte alignment
0x00010dbfa5d8: note: pointer points here
 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00
              ^
db/version_set.cc:522:9: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:522:9: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
db/version_set.cc:522:24: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:522:38: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:522:57: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:522:57: runtime error: load of misaligned address 0x00010dbfa678 for type 'rocksdb::RangeDelAggregator *', which requires 16 byte alignment
0x00010dbfa678: note: pointer points here
 01 00 00 00  d0 a1 bf 0d 01 00 00 00  00 00 00 00 00 00 00 00  f8 db 70 0a 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:523:54: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:523:54: runtime error: load of misaligned address 0x00010dbfa668 for type 'rocksdb::HistogramImpl *', which requires 16 byte alignment
0x00010dbfa668: note: pointer points here
 01 00 00 00  c8 88 a5 0d 01 00 00 00  00 00 00 00 01 00 00 00  d0 a1 bf 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:524:9: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:524:47: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:524:62: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/table_cache.cc:228:33: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
table/block_based_table_reader.cc:1554:41: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
table/block_based_table_reader.cc:1396:21: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
include/rocksdb/options.h:931:8: runtime error: reference binding to misaligned address 0x00010dbfa628 for type 'const std::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1584:13: runtime error: load of misaligned address 0x00010dbfa648 for type '__base *const' (aka '__base<void ()> *const'), which requires 16 byte alignment
0x00010dbfa648: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  c8 a5 97 0d 01 00 00 00  38 36 9b 0d
              ^
table/block_based_table_reader.cc:1555:24: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
db/table_cache.cc:244:54: runtime error: load of misaligned address 0x00010dbfa618 for type 'const bool', which requires 16 byte alignment
0x00010dbfa618: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
db/table_cache.cc:246:49: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
db/version_set.cc:532:12: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
db/version_set.cc:532:12: runtime error: member access within misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
db/version_set.cc:532:26: runtime error: load of misaligned address 0x00010dbfa5f8 for type 'const rocksdb::Slice *const', which requires 16 byte alignment
0x00010dbfa5f8: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
version_set.cc:493: runtime error: member call on misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment
0x00010dbfa5c8: note: pointer points here
 00 00 00 00  a0 db 70 0a 01 00 00 00  00 00 00 00 00 00 00 00  90 14 98 0d 01 00 00 00  00 00 00 00
              ^
version_set.cc:493: runtime error: member call on misaligned address 0x00010dbfa5e8 for type 'rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
options.h:931: runtime error: member call on misaligned address 0x00010dbfa5e8 for type 'rocksdb::ReadOptions', which requires 16 byte alignment
0x00010dbfa5e8: note: pointer points here
 00 00 00 00  01 01 ff ff ff ff ff ff  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
options.h:931: runtime error: member call on misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
functional:1765: runtime error: member call on misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1766:9: runtime error: member access within misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1766:9: runtime error: load of misaligned address 0x00010dbfa648 for type '__base *' (aka '__base<void ()> *'), which requires 16 byte alignment
0x00010dbfa648: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  c8 a5 97 0d 01 00 00 00  38 36 9b 0d
              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1766:27: runtime error: member access within misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1768:14: runtime error: member access within misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment
0x00010dbfa628: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1768:14: runtime error: load of misaligned address 0x00010dbfa648 for type '__base *' (aka '__base<void ()> *'), which requires 16 byte alignment
0x00010dbfa648: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  c8 a5 97 0d 01 00 00 00  38 36 9b 0d
              ^
[       OK ] DBPropertiesTest.ReadLatencyHistogramByLevel (1599 ms)
[----------] 1 test from DBPropertiesTest (1599 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1599 ms total)
[  PASSED  ] 1 test.
```

So it seems the root cause is that the internal implementation of `std::function` on macOS (and perhaps with libc++ generally?) requires 16-byte aligned memory, but the arena allocator only guarantees that the returned memory will be `sizeof(void*)` aligned, which is only 8-byte alignment on my machine. This patch solves the problem by adjusting the allocator to derive the necessary alignment from `alignof(std::max_align_t)`, which is properly 16 bytes on my machine.

As I mentioned in #2265, none of RocksDB's tests will cause this unaligned access to actually abort the process, but, on macOS, linking CockroachDB against a version of RocksDB with the above patch and letting it run for just a few seconds will cause a SIGABRT.

```
Process 19792 stopped
* thread #2, stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
    frame #0: 0x0000000004f5e78f cockroach`DBNewIter + 95
cockroach`DBNewIter:
->  0x4f5e78f <+95>:  callq  *0x28(%rax)
    0x4f5e792 <+98>:  jmp    0x4f5e79e                 ; <+110>
    0x4f5e794 <+100>: movq   -0x50(%rbp), %rcx
    0x4f5e798 <+104>: movq   %rax, %rdi
(lldb) bt
* thread #2, stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
  * frame #0: 0x0000000004f5e78f cockroach`DBNewIter + 95
```

I'd get you a backtrace, but [Go doesn't include cgo debug information on macOS](https://github.com/golang/go/issues/6942). I've also tried building against libc++ on Linux, where debug information would be available, but I can't seem to trigger the bug there.

In any case, this PR both fixes the segfault in CockroachDB and fixes the warnings reported by ubsan.
Closes https://github.com/facebook/rocksdb/pull/2347

Differential Revision: D5108596

Pulled By: yiwu-arbug

fbshipit-source-id: bd5e4323b2ce915ed4fe78e123cb8996aec75a00

db/column_family_test.cc

@@ -933,62 +933,62 @@ TEST_F(ColumnFamilyTest, FlushTest) {
 TEST_F(ColumnFamilyTest, LogDeletionTest) {
   db_options_.max_total_wal_size = std::numeric_limits<uint64_t>::max();
   column_family_options_.arena_block_size = 4 * 1024;
-  column_family_options_.write_buffer_size = 100000;  // 100KB
+  column_family_options_.write_buffer_size = 128000;  // 128KB
   Open();
   CreateColumnFamilies({"one", "two", "three", "four"});
   // Each bracket is one log file. if number is in (), it means
   // we don't need it anymore (it's been flushed)
   // []
   AssertCountLiveLogFiles(0);
-  PutRandomData(0, 1, 100);
+  PutRandomData(0, 1, 128);
   // [0]
-  PutRandomData(1, 1, 100);
+  PutRandomData(1, 1, 128);
   // [0, 1]
-  PutRandomData(1, 1000, 100);
+  PutRandomData(1, 1000, 128);
   WaitForFlush(1);
   // [0, (1)] [1]
   AssertCountLiveLogFiles(2);
-  PutRandomData(0, 1, 100);
+  PutRandomData(0, 1, 128);
   // [0, (1)] [0, 1]
   AssertCountLiveLogFiles(2);
-  PutRandomData(2, 1, 100);
+  PutRandomData(2, 1, 128);
   // [0, (1)] [0, 1, 2]
-  PutRandomData(2, 1000, 100);
+  PutRandomData(2, 1000, 128);
   WaitForFlush(2);
   // [0, (1)] [0, 1, (2)] [2]
   AssertCountLiveLogFiles(3);
-  PutRandomData(2, 1000, 100);
+  PutRandomData(2, 1000, 128);
   WaitForFlush(2);
   // [0, (1)] [0, 1, (2)] [(2)] [2]
   AssertCountLiveLogFiles(4);
-  PutRandomData(3, 1, 100);
+  PutRandomData(3, 1, 128);
   // [0, (1)] [0, 1, (2)] [(2)] [2, 3]
-  PutRandomData(1, 1, 100);
+  PutRandomData(1, 1, 128);
   // [0, (1)] [0, 1, (2)] [(2)] [1, 2, 3]
   AssertCountLiveLogFiles(4);
-  PutRandomData(1, 1000, 100);
+  PutRandomData(1, 1000, 128);
   WaitForFlush(1);
   // [0, (1)] [0, (1), (2)] [(2)] [(1), 2, 3] [1]
   AssertCountLiveLogFiles(5);
-  PutRandomData(0, 1000, 100);
+  PutRandomData(0, 1000, 128);
   WaitForFlush(0);
   // [(0), (1)] [(0), (1), (2)] [(2)] [(1), 2, 3] [1, (0)] [0]
   // delete obsolete logs -->
   // [(1), 2, 3] [1, (0)] [0]
   AssertCountLiveLogFiles(3);
-  PutRandomData(0, 1000, 100);
+  PutRandomData(0, 1000, 128);
   WaitForFlush(0);
   // [(1), 2, 3] [1, (0)], [(0)] [0]
   AssertCountLiveLogFiles(4);
-  PutRandomData(1, 1000, 100);
+  PutRandomData(1, 1000, 128);
   WaitForFlush(1);
   // [(1), 2, 3] [(1), (0)] [(0)] [0, (1)] [1]
   AssertCountLiveLogFiles(5);
-  PutRandomData(2, 1000, 100);
+  PutRandomData(2, 1000, 128);
   WaitForFlush(2);
   // [(1), (2), 3] [(1), (0)] [(0)] [0, (1)] [1, (2)], [2]
   AssertCountLiveLogFiles(6);
-  PutRandomData(3, 1000, 100);
+  PutRandomData(3, 1000, 128);
   WaitForFlush(3);
   // [(1), (2), (3)] [(1), (0)] [(0)] [0, (1)] [1, (2)], [2, (3)] [3]
   // delete obsolete logs -->

util/arena.cc

@@ -33,7 +33,7 @@ const size_t Arena::kInlineSize;
 
 const size_t Arena::kMinBlockSize = 4096;
 const size_t Arena::kMaxBlockSize = 2u << 30;
-static const int kAlignUnit = sizeof(void*);
+static const int kAlignUnit = alignof(max_align_t);
 
 size_t OptimizeBlockSize(size_t block_size) {
   // Make sure block_size is in optimal range

util/arena.h

@@ -82,7 +82,7 @@ class Arena : public Allocator {
   }
 
  private:
-  char inline_block_[kInlineSize] __attribute__((__aligned__(sizeof(void*))));
+  char inline_block_[kInlineSize] __attribute__((__aligned__(alignof(max_align_t))));
   // Number of bytes allocated in one block
   const size_t kBlockSize;
   // Array of new[] allocated memory blocks

util/arena_test.cc

@@ -91,14 +91,15 @@ static void ApproximateMemoryUsageTest(size_t huge_page_size) {
   ASSERT_EQ(kZero, arena.ApproximateMemoryUsage());
 
   // allocate inline bytes
+  const size_t kAlignUnit = alignof(max_align_t);
   EXPECT_TRUE(arena.IsInInlineBlock());
-  arena.AllocateAligned(8);
+  arena.AllocateAligned(kAlignUnit);
   EXPECT_TRUE(arena.IsInInlineBlock());
-  arena.AllocateAligned(Arena::kInlineSize / 2 - 16);
+  arena.AllocateAligned(Arena::kInlineSize / 2 - (2 * kAlignUnit));
   EXPECT_TRUE(arena.IsInInlineBlock());
   arena.AllocateAligned(Arena::kInlineSize / 2);
   EXPECT_TRUE(arena.IsInInlineBlock());
-  ASSERT_EQ(arena.ApproximateMemoryUsage(), Arena::kInlineSize - 8);
+  ASSERT_EQ(arena.ApproximateMemoryUsage(), Arena::kInlineSize - kAlignUnit);
   ASSERT_PRED2(CheckMemoryAllocated, arena.MemoryAllocatedBytes(),
                Arena::kInlineSize);