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

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Date:   Tue, 13 Dec 2016 02:07:42 +0100
From:   Stanislav Kozina <skozina@...hat.com>
To:     Dodji Seketeli <dodji@...eteli.org>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Ian Campbell <ijc@...lion.org.uk>, Michal Marek <mmarek@...e.com>,
        Ben Hutchings <ben@...adent.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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

Hello,

>> That said, a dwarf based checker tool should be able to do as good a job
>> (maybe a bit better because report is very informative and it may pick up
>> compiler alignments or padding options).
> So, Nicholas was kind enough to send me the two Linux Kernel binaries
> that he built with the tiny little interface change that we were
> discussing earlier.  Here is what the abidiff[1] tools says about that
> interface change:

Thanks Nicholas and Dodji for this great example, for comparison I think 
it would be nice to share the example run with kabi-dw too.
kabi-dw first dumps and unifies all type information into a set of text 
files, the unification takes a significant time. Then the two sets of 
these text files can be compared.

An example run would look like:
$ time ~/Code/kabi-dw/kabi-dw generate -o abi1 vmlinux.abi1
Generating symbol defs from vmlinux.abi1...

real    0m29.057s
user    0m13.929s
sys    0m14.862s
$ time ~/Code/kabi-dw/kabi-dw generate -o abi2 vmlinux.abi2
Generating symbol defs from vmlinux.abi2...

real    0m29.134s
user    0m13.961s
sys    0m14.921s
$ time ~/Code/kabi-dw/kabi-dw compare abi1 abi2
Changes detected in: 
home/npiggin/src/linux.vectors/mm/memory.c/struct--blah.txt
Inserted:
+0x0 int y;
Shifted:
-0x0 int x;
+0x4 int x;


real    0m0.176s
user    0m0.135s
sys    0m0.040s

The size of the generated text files with all the relevant type 
information is as follows:
$ du -hs abi1
16M    abi1
$ find abi1 -type f | wc -l
3162

Warm regards,
-Stanislav