On Fri, Nov 06, 2020 at 11:55:23AM -0500, Steven Rostedt wrote: > On Fri, 6 Nov 2020 17:45:37 +0100 > Johan Hovold <johan@xxxxxxxxxx> wrote: > > > It's simply specifying alignment when declaring the variable that > > prevents this optimisation. The relevant code is in the function > > align_variable() in [1] where DATA_ALIGNMENT() is never called in case > > an alignment has been specified (!DECL_USER_ALIGN(decl)). > > > > There's no mention in the documentation of this that I'm aware of, but > > this is the way the aligned attribute has worked since its introduction > > judging from the commit history. > > > > As mentioned above, we've been relying on this for kernel parameters and > > other structures since 2003-2004 so if it ever were to change we'd find > > out soon enough. > > > > It's about to be used for scheduler classes as well. [2] > > Is this something that gcc folks are aware of? Yes, we appear to be relying > on undocumented implementations, but that hasn't caused gcc to break the > kernel in the past. The scheduler change was suggested by Jakub so at least some of them are. Johan
