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Date: Fri, 6 Nov 2020 11:55:23 -0500 From: Steven Rostedt <rostedt@...dmis.org> To: Johan Hovold <johan@...nel.org> Cc: Jessica Yu <jeyu@...nel.org>, linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, Rob Herring <robh+dt@...nel.org>, Frank Rowand <frowand.list@...il.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Nick Desaulniers <ndesaulniers@...ogle.com>, Arnd Bergmann <arnd@...db.de>, Geert Uytterhoeven <geert@...ux-m68k.org>, Dmitry Torokhov <dmitry.torokhov@...il.com>, David Miller <davem@...emloft.net>, Jakub Jelinek <jakub@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Daniel Kurtz <djkurtz@...omium.org>, linux-arch@...r.kernel.org, linux-m68k@...ts.linux-m68k.org Subject: Re: [PATCH 0/8] linker-section array fix and clean ups On Fri, 6 Nov 2020 17:45:37 +0100 Johan Hovold <johan@...nel.org> 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. -- Steve
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