Misaligned memory reads in lmdb

[ahoppen]

To reproduce run

UBSAN_OPTIONS=halt_on_error=true ~/swift-latest/usr/bin/swift test --sanitize=undefined --filter testBackgroundIndexingHappensWithLowPriority

Output

Test Case '-[SourceKitLSPTests.BackgroundIndexingTests testBackgroundIndexingHappensWithLowPriority]' started.
/Users/alex/src/sourcekit-lsp/.command-line-build/checkouts/indexstore-db/lib/Database/lmdb/mdb.c:5916:14: runtime error: load of misaligned address 0x000109ddfffd for type 'unsigned short', which requires 2 byte alignment
0x000109ddfffd: note: pointer points here
 f6 57 eb d1 cf fb 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
             ^ 
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /Users/alex/src/sourcekit-lsp/.command-line-build/checkouts/indexstore-db/lib/Database/lmdb/mdb.c:5916:14 in 

[ahoppen]

Synced to Apple’s issue tracker as rdar://129444473