Обсуждение: More bogus alignment assumptions

Following up on the recent bug report from Steve Nicolai, I spent a
tedious hour groveling through all the warnings emitted by gcc with
-Wcast-align.  (We ought to try to reduce the number of them, but that's
a task for another day.)

I found seven places, in addition to the tuptoaster.c error originally
identified by Steve, in which the code is assuming that a "char foo[N]"
local variable will be aligned on better-than-char boundaries by the
compiler.  All were inserted since 7.0.  All but one were inserted by
Vadim in the new WAL code; the other one is in large-object support
and is my fault :-(

I will fix these shortly, but I wanted to raise a flag to people:
don't do that.  An array of X is not guaranteed to be aligned any
better than an X is.
        regards, tom lane

> Following up on the recent bug report from Steve Nicolai, I spent a
> tedious hour groveling through all the warnings emitted by gcc with
> -Wcast-align.  (We ought to try to reduce the number of them, but that's
> a task for another day.)
> 
> I found seven places, in addition to the tuptoaster.c error originally
> identified by Steve, in which the code is assuming that a "char foo[N]"
> local variable will be aligned on better-than-char boundaries by the
> compiler.  All were inserted since 7.0.  All but one were inserted by
> Vadim in the new WAL code; the other one is in large-object support
> and is my fault :-(
> 
> I will fix these shortly, but I wanted to raise a flag to people:
> don't do that.  An array of X is not guaranteed to be aligned any
> better than an X is.

Added to TODO:
* Remove warnings created by -Wcast-align

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