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We want this struct to be exactly a series of 3 int16 words, no more and no less. Historically, at least, some ARM compilers preferred to pad it to 8 bytes unless coerced. Our old way of doing that was just to use __attribute__((packed)), but as pointed out by Piotr Stefaniak, that does too much: it also licenses the compiler to give the struct only byte-alignment. We don't want that because it adds access overhead, possibly quite significant overhead. According to the GCC manual, what we want requires also specifying __attribute__((align(2))). It's not entirely clear if all the relevant compilers accept this pragma as well, but we can hope the buildfarm will tell us if not. We can also add a static assertion that should fire if the compiler padded the struct. Since the combination of these pragmas should define exactly what we want on any compiler that accepts them, let's try using them wherever we think they exist, not only for __arm__. (This is likely to expose that the conditional definitions in c.h are inadequate, but finding that out would be a good thing.) The immediate motivation for this is that the current definition of ExecRowMark allows its curCtid field to be misaligned. It is not clear whether there are any other uses of ItemPointerData with a similar hazard. We could change the definition of ExecRowMark if this doesn't work, but it would be far better to have a future-proof fix. Piotr Stefaniak, some further hacking by me
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.