linux-kernel - Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

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Date:   Fri, 9 Dec 2016 15:36:04 +0100
From:   Stanislav Kozina <skozina@...hat.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Don Zickus <dzickus@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ben Hutchings <ben@...adent.org.uk>,
        Michal Marek <mmarek@...e.com>,
        Adam Borowski <kilobyte@...band.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Debian kernel maintainers <debian-kernel@...ts.debian.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from
 asm

>>>> The question is how to provide a similar guarantee if a different way?
>>> As a tool to aid distro reviewers, modversions has some value, but the
>>> debug info parsing tools that have been mentioned in this thread seem
>>> superior (not that I've tested them).
>> On the other hand the big advantage of modversions is that it also
>> verifies the checksum during runtime (module loading). In other words, I
>> believe that any other solution should still generate some form of
>> checksum/watermark which can be easily checked for compatibility on
>> module load.
>> It should not be hard to add to the DWARF based tools though. We'd just
>> parse DWARF data instead of the C code.
> A runtime check is still done, with per-module vermagic which distros
> can change when they bump the ABI version. Is it really necessary to
> have more than that (i.e., per-symbol versioning)?

 From my point of view, it is. We need to allow changing ABI for some 
modules while maintaining it for others.
In fact I think that there should be version not only for every exported 
symbol (in the EXPORT_SYMBOL() sense), but also for every public type 
(in the sense of eg. structure defined in the public header file).

Thanks,
-Stanislav