[ moved to -hackers ] Greg Stark <st...@mit.edu> writes: > Back in 2001 a hack to add __attribute__((packed)) to ItemPtr was > added with a comment "Appropriate whack upside the head for ARM" > (dcbbdb1b3ee). I don't know if this is still a factor in 2016 or not > but it has already resulted in some collateral damage in 2015 when > some compiler took that as license to align the whole struct on single > byte alignment when it was buried inside another struct > (d4b538ea367de).
> I just tried compiling with Clang 3.8.0 and got tons of warnings about > this because: > 'ItemPointerData' may result in an unaligned pointer value > [-Waddress-of-packed-member] > ...ItemPointerGetBlockNumber(&(xlrec->target_tid)), > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > ../../../src/include/storage/itemptr.h:69:25: note: expanded from macro > 'ItemPointerGetBlockNumber' > BlockIdGetBlockNumber(&(pointer)->ip_blkid) \ > ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~ > ../../../src/include/storage/block.h:118:19: note: expanded from macro > 'BlockIdGetBlockNumber' > (BlockNumber) (((blockId)->bi_hi << 16) | ((uint16) > (blockId)->bi_lo)) \ > ^~~~~~~ > Which seems to indicate that clang may not understand the > "pg_attribute_aligned(2)" or perhaps it does and just doesn't take it > into account when generating these warnings. Ick. Can you look to see how those macros are expanding on your clang? > I'm sure there are other people testing clang -- isn't it the default > on MacOS? Do they not see these warnings? I've never seen this on MacOS. The current compiler version (on Sierra) is $ gcc -v Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/c++/4.2.1 Apple LLVM version 8.0.0 (clang-800.0.38) Target: x86_64-apple-darwin16.0.0 Thread model: posix InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin Don't know how that version number compares to "3.8.0". regards, tom lane -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers