Re: [PATCH v2 0/4] export/modpost: avoid renaming __ksymtab entries for symbol namespaces

From: Luis Chamberlain <mcgrof@kernel.org>
To: Matthias Maennich <maennich@google.com>
Cc: linux-kernel@vger.kernel.org, kernel-team@android.com,
	Jessica Yu <jeyu@kernel.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Martijn Coenen <maco@android.com>,
	Lucas De Marchi <lucas.de.marchi@gmail.com>,
	Shaun Ruffell <sruffell@sruffell.net>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Will Deacon <will@kernel.org>,
	linux-kbuild@vger.kernel.org, linux-modules@vger.kernel.org
Subject: Re: [PATCH v2 0/4] export/modpost: avoid renaming __ksymtab entries for symbol namespaces
Date: Thu, 24 Oct 2019 10:24:24 +0000	[thread overview]
Message-ID: <20191024102424.GL11244@42.do-not-panic.com> (raw)
In-Reply-To: <20191024093546.GB199239@google.com>

On Thu, Oct 24, 2019 at 10:35:46AM +0100, Matthias Maennich wrote:
> On Wed, Oct 23, 2019 at 12:22:22PM +0000, Luis Chamberlain wrote:
> > On Fri, Oct 18, 2019 at 10:31:39AM +0100, Matthias Maennich wrote:
> > > The introduction of the symbol namespace patches changed the way symbols are
> > > named in the ksymtab entries. That caused userland tools to fail (such as
> > > kmod's depmod). As depmod is used as part of the kernel build it was worth
> > > having another look whether this name change can be avoided.
> > 
> > Why have this as a default feature? What about having an option to
> > disable this feature? The benefit being that without a full swing of
> > tests to avoid regressions its not clear what other issues may creep
> > up. With this as optional, those wanting the mechanism can enable it
> > and happilly find the issues for those more conservative.
> 
> The strongest argument against that is, that the 'conservative' people
> would constantly break things for the more 'adventurous' ones. They
> would introduce namespace requirements by just using symbols without
> correctly adjusting the imports.
> 
> Second, vmlinux and modules would have to be compiled in the same
> configuration. Otherwise they are incompatible and we would likely have
> to maintain code in the module loader to catch issues caused by that.
> In general, I think for the adoption of this feature and one of its
> purposes - making unexpected use of symbols across the tree visible
> already at review time - we should not make this an optional one.
> Enforcing the imports at module load time is optional (there is an
> option).
> 
> And finally, having that code configurable for both options introduces
> quite some complexity in kernel/module.c, modpost and
> include/linux/export.h that would make the code hard to maintain and
> complex to test. Hence that would likely introduce more issues.
> 
> I know the feature came with some rough edges. Sorry about that. I
> think, we got most of them worked out pretty well (big thanks to
> Masahiro and Jessica and others helping with that). Now the actual
> change to the surface exposed to userland tools is much smaller and the
> feature itself less intrusive.

This logic makes sense, the complexity over module loading is already
high and supporting yet another division would be a burden for review
and maintenace.

However I'd feel much more inclined to support such decisions when and if
we had a series of test cases to prevent possible regressions. Since
effort with testing will move forward, I'm happy with the status quo.

  Luis