Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from
 asm
To: Nicholas Piggin <npiggin@gmail.com>,
        Ben Hutchings <ben@decadent.org.uk>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Adam Borowski <kilobyte@angband.pl>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Debian kernel maintainers <debian-kernel@lists.debian.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dodji Seketeli <dodji@seketeli.org>
From: Michal Marek <mmarek@suse.com>
Message-ID: <6e8cf20b-2d2f-ba1f-e02c-c757d5a25db7@suse.com>
Date: Thu, 1 Dec 2016 17:12:41 +0100
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On 2016-12-01 04:39, Nicholas Piggin wrote:
> On Thu, 01 Dec 2016 02:35:54 +0000
> Ben Hutchings <ben@decadent.org.uk> wrote:
>> As I understand it, genksyms incorporates the definitions of a
>> function's parameter and return types - not just their names - and all
>> the types they refer to, recursively.  So a structure size change
>> should change the version of all functions where the function and its
>> caller pass that structure between them, however indirectly.  It finds
>> such indirect ABI breakage for me fairly regularly, though of course I
>> don't know that it finds everything.
> 
> It is only the type name.
> 
> Not only that but even if you did extend it further to structure type
> arrangement then you still have to deal with other structures followed
> via pointers. Or (rarer but not unheard of):
> 
> - changes to structures without changes of the types of their members
> - changes to arguments without changes of their type

This is already covered by genksyms. Try make V=1 with
CONFIG_MODVERSIONS=y and add the -D option to one of the genksyms
command. I wanted to paste the expanded signature for
register_filesystem() as an example, but vger would probably drop the
mail for being too big :).


> - changes to semantics of functions
> - data structures derived in ways other than exported symbols, e.g.,
>   fixed register for `current` on some archs

Right, this is something that genksyms has no idea about.

Michal