linux-kernel - Re: [PATCH] kbuild: Remove CONFIG_DEBUG_SECTION

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Message-ID: <YlCfhUkOXTvqCfjT@hirez.programming.kicks-ass.net>
Date:   Fri, 8 Apr 2022 22:48:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>, X86 ML <x86@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Changbin Du <changbin.du@...il.com>,
        linux-toolchains@...r.kernel.org,
        clang-built-linux <llvm@...ts.linux.dev>
Subject: Re: [PATCH] kbuild: Remove CONFIG_DEBUG_SECTION_MISMATCH

On Fri, Apr 08, 2022 at 10:32:28PM +0200, Peter Zijlstra wrote:

> > > This weird option is having us upgrade quite a few 'inline' to
> > > '__always_inline'.
> > 
> > As is, the assumption that __init functions only call other __init
> > functions or __always_inline is a brittle house of cards that leads to
> > a "what color is your function" [0] scenario, and leads to code that
> > happens to not emit warnings for compiler X (or compiler X version Y).
> > There's also curious exceptions in modpost that look like memory leaks
> > to me.

So I don't see __always_inline that way (also I'm in the 'inline' should
be '__always_inline' camp).

To me inline is more like: 'instantiate that pattern *here*'. It's like
CPP macros, only less horrible. You get the code generated according to
the local rules (instrumentation yes/no, section, and whatever other
function attributes we have that affect code-gen).

So with inline we can get the same pattern instantiated a number of
different times, leading to different actual code, without having to
type the whole thing multiple times (which would be terrible for
maintenance) etc..

Combine __always_inline with constant propagation of inline function
'pointers' and you get do beautiful things ;-) /me runs