linux-kernel - Re: [PATCH AUTOSEL 4.9 4/4] init/gcov: allow CONFIG

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Date:   Mon, 08 Feb 2021 19:25:21 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Sasha Levin <sashal@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>, Jessica Yu <jeyu@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH AUTOSEL 4.9 4/4] init/gcov: allow CONFIG_CONSTRUCTORS on
 UML to fix module gcov

On Mon, 2021-02-08 at 18:00 +0000, Sasha Levin wrote:
> From: Johannes Berg <johannes.berg@...el.com>
> 
> [ Upstream commit 55b6f763d8bcb5546997933105d66d3e6b080e6a ]
> 
> On ARCH=um, loading a module doesn't result in its constructors getting
> called, which breaks module gcov since the debugfs files are never
> registered.  On the other hand, in-kernel constructors have already been
> called by the dynamic linker, so we can't call them again.
> 
> Get out of this conundrum by allowing CONFIG_CONSTRUCTORS to be
> selected, but avoiding the in-kernel constructor calls.
> 
> Also remove the "if !UML" from GCOV selecting CONSTRUCTORS now, since we
> really do want CONSTRUCTORS, just not kernel binary ones.
> 
> Link: https://lkml.kernel.org/r/20210120172041.c246a2cac2fb.I1358f584b76f1898373adfed77f4462c8705b736@changeid
> 


While I don't really *object* to this getting backported, it's also a
(development) corner case that somebody wants gcov and modules in
ARCH=um ... I'd probably not backport this.

johannes